Sierra Wireless DART 200 CDPD User Manual

Download

DART 200 CDPD Modem

For CDPD Versions 1.0 and 1.1

User’s Guide

Firmware Version 3.0.10

Revision 1.0

Part Number: 1197-00

January 1998

DART 200 CDPD Modem User's Guide

NOTE: This guide provides the information necessary to program the Data Access Radio Transceiver (DART) 200 for operation on Cellular Digital Packet Data (CDPD) 1.0 or 1.1 networks. The factory default is for 1.1 mode. If you need to operate in CDPD 1.0 mode, refer to Selecting CDPD 1.0 or 1.1 mode of operation, p. 2-8, for detailed instructions.

The guide provides information for use with the current released version of the DART 200 software (3.0.10). See the ATI command in Appendix F, DART AT Commands, to determine the firmware version your DART 200 is currently using. If you need a prior or newer version of the software please contact Sierra Wireless for the desired download package.

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Important Notice

The Data Access Radio Transceiver (DART) can only be exported from the US, or re-exported to another country with the issuance of an export license from the US Government. Contact Sierra Wireless for more information.

Because of the nature of wireless communications, transmission and reception of data can never be guaranteed. Data can be delayed, corrupted, or be totally lost. Although significant delays or losses of data are rare when wireless devices such as DART are used in a normal manner with a well-constructed network. DART should not be used in situations where failure to transmit or receive data could result in damage of any kind to the user or any other party, including but not limited to personal injury, death, or loss of property. Sierra Wireless, Inc., accepts no responsibility for damages of any kind resulting from delays or errors in data transmitted or received using DART, or for failure of DART to transmit or receive such data.

Contact Information

Sierra Wireless, Inc. 260 - 13151 Vanier Place, Richmond, BC, Canada V2V 2J2 Tel. 604.231.1100 or 313.528.5880 Fax. 604.231.1109 Email: support@sierrawireless.com Web site: www.sierrawireless.com

First Printing: January, 1998. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without

the prior permission of the publisher. AT is a trademark of Hayes Microcomputer Products, Inc. Hayes is a registered trademark of Hayes Microcomputer Products, Inc. All other trademarks are owned by their respective companies. The information in this guide is subject to change without notice and does not represent a commitment on the part of Sierra

Wireless, Inc. Sierra Wireless, Inc. shall not be liable for incidental or consequential damages resulting from the furnishing, performance, or use of this manual

Safety and Hazards

Do not operate the Sierra Wireless modem in areas where blasting is in progress, where explosive atmospheres may be present, near medical equipment, near life support equipment, or any equipment which may be susceptible to any form of radio interference. In such areas, the Sierra Wireless modem MUST BE TURNED OFF. The Sierra Wireless modem can transmit signals which could interfere with this equipment.

Do not operate the Sierra Wireless modem in any aircraft, whether the aircraft is on the ground or in flight. In aircraft, the Sierra Wireless modem MUST BE TURNED OFF. The reason for this is that when operating in the CDPD or cellular circuit switched mode, the Sierra Wireless modem can transmit signals which could interfere with various onboard equipment systems.

The driver or operator of any vehicle should not operate the Sierra Wireless modem while in control of a vehicle. Doing so will detract from the driver or operator’s control and operation of that vehicle. In some states and provinces, operating such communications devices while in control of a vehicle is an offence.

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DART 200 CDPD Modem User’s Guide

Contents

Figures xi

Tables xii

About This Guide xiii

Who should read this guide xiii

Skills required to use this guide xiii

What is in this guide xiii

Changes and additions to this guide xiv

Related reading

Additional information regarding the CDPD network and communication information can be found in the following references:

• Cellular Digital Packet Data System Specification, CDPD Forum,

401 N. Michigan Ave., Chicago, IL 60611, (tel.) 800.335.CDPD

• TCP/IP, Running a Successful Network, K. Washburn and J.T.

Evans, NY, Addison-Wesley, 1993

• Internetworking with TCP/IP, D.E. Comer, N.J., Prentice Hall, 1991

• The Whole Internet, E. Krol, Sabastopol, CA, 1992,

(tel.) 800.998.9938

• Computer Networks, A.S. Tannenbaum, N.J., Prentice Hall, 1989

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DART 200 CDPD Modem User’s Guide About This Guide

Compliances

FCC

This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to Part 15 of the FCC rules. These limits

NOTE: This unit was tested with shielded cables on the peripheral devices. Shielded cables must be used with the unit to insure compliance.

provide reasonable protection against harmful interference in residential installations. This equipment generates, uses and can radiate radio frequency energy and, if not installed and used in accordance with the instructions, can cause harmful interference to radio communications. However, there is no guarantee that interference will not occur in a particular installation. If this equipment does cause harmful interference to radio or television reception, determined by turning the equipment off and on, try to correct the interference by one or more of the following measures:

• Reorient or relocate the receiving antenna

NOTE: The manufacturer is not responsible for any radio or TV interference caused by unauthorized modifications to this equipment. Such modification could void the user’s authority to operate the equipment.

• Increase the separation between the equipment and receiver

• Connect the equipment to an outlet on a circuit different from the

circuit the receiver is connected to

• Consult the dealer or an experienced radio/TV technician for help

Changes or modifications not expressly approved by the manufacturer can void the user’s authority to operate the equipment.

Canadian

“This digital apparatus does not exceed the Class B limits for radio noise emissions from digital apparatus as set out in the interference causing equipment standard entitled ‘Digital Apparatus’, ICES-003 of the Department of Communications.”

“Cet appareil numerique respecte les limites de bruits radioelectriques applicables aux appareils numeriques de Classe B prescrites dans la norme sur le materiel brouilleur: ‘Appareils Numeriques’, NHB-003 edictee par le ministre des Communications.”

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DART 200 CDPD Modem User’s Guide About This Guide

injury.

Safety information

A caution in the margin, as shown at the left or in the body of the text, denotes a procedure or practice if not performed correctly could result in

CAUTION: A caution calls attention to a procedure or practice if not performed correctly could result in loss of data or damage to equipment.

WARNING: Denotes a hazard. A warning calls attention to a procedure or practice if not performed correctly could result in personal

loss of data, or damage to equipment.

A warning in the margin, as shown at the left or included within the body of the text denotes a hazard. A caution calls attention to a procedure or practice if not performed correctly could result in personal injury.

Conventions used in this guide

The following conventions are used in this guide to help readers locate and interpret information easily.

Italics Italicized text is used for book titles, and for

cross-referencing chapter titles, and subsections within chapters. In cross-references the most specific item, usually, the last item, is italicized, for example:

• Chapter 1, Introduction

• Chapter 1, Introduction, Description

Courier

Courier text is used to show on-screen text, for example:

at\s? * NEI 0 = IP ADDRESS 198.225.189.032 GMID 00000 OK

SMALL CAPS

Small capitals are used for key names, key combinations, and key sequences, for example:

Press ENTER.

ALL CAPS All capitals are used to show the connection states

of the DART, for example, CONNECT.

Bold

Bold text is used to emphasize the AT commands, for example, AT\N.

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1 Introduction

Power

Chapter

Description

The Data Access Radio Transceiver (DART) 200, as shown in Figure 1-1, is a wireless, multipurpose, programmable modem that provides reliable, cost effective mobile and fixed communications over the Cellular Digital Packet Data (CDPD) network. It is a 3-watt, half-duplex device operating on a regulated 12 volts @ 2.5 amps, and contains flash memory to allow software upgrades to be made in the field. The DART 200 differs from its predecessor, the DART 100, in that it has the flash memory to enable field download of software upgrades.

Figure 1-1. DART 200 front view

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Power connection 12VDC*

Data input RS-232 DB-9 Connector

Switch

Power On indicator and RSSI

*Molex Micro-Fit 3.0 4305-0200 - Mates with Molex 43025-0200 on cable.

The modem is lightweight (only 12 ounces), with a small form factor (6.3” x 3.4” x 1.0”). Its rugged construction makes it well suited for industrial and commercial applications of all kinds.

The DART 200 firmware supports either CDPD V1.0 or CDPD V1.1. The present version of the modem comes pre-selected for CDPD V1.1. This selection can be altered by modifying an Status (S)-Register. Refer to Selecting CDPD 1.0 or 1.1 mode of operation, p. 2-8, for details.

DART 200 CDPD Modem User’s Guide 1 Introduction

From a networking perspective, the modem has complete built-in Transmission Control Protocol (TCP), User Datagram Protocol (UDP), Serial Line Internet Protocol (SLIP), and telnet protocols. Network communications can be achieved without the attached end-user device having to provide an integrated TCP or UDP capability. Select the desired built-in protocol included in the DART 200 by using the appropriate AT dial command and begin your data transfer. The end-user can put the DART 200 in SLIP mode, providing an external software stack, if desired.

A power cord with connector is supplied with each DART 200, and one copy of this User’s Guide is included with each order. A power supply and cellular antennas are available as options at additional cost.

New for this version

If you have prior experience with the DART 200, major differences and enhancements between the old modem software (3.0.9 dated 7/2/96 and earlier) and the current version are:

• Provides the “friends only” feature for TCP in addition to UDP

• The automatic SLIP restart feature is now available

DART 200 accessories and services

RF accessories Power accessories

Hardware options Software options Services

• 3 dB cellular magnetic mount antenna

• 110 VAC to 12 VDC @2.5 amps power

supply

• Mounting bracket

• V.42 bis data compression

• Developers package

• DART technical training

Migration considerations

If you are migrating applications from prior versions of the DART 200 software to the current version, there are no changes in this version that alter existing application operation to be aware of. However, to use TCP Friends Only mode or Auto SLIP restart, some alteration can be required.

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DART 200 CDPD Modem User’s Guide 1 Introduction

Contacting your cellular carrier

There are currently two cellular carriers in each market area: the A side carrier and the B side carrier. Each carrier can potentially install and enable CDPD on their cellular network. The CDPD network allows end-users to visit the regions of other carriers, as well as move within their home cellular system.

Contact your cellular provider to get an IP Address for your modem. This IP address lets you operate the modem on the CDPD network. Although the modem can perform some basic functions without an IP

NOTE:

The EID is found on the label on the bottom of your DART 200.

Address, it cannot register, ping, or run end-user applications. Your carrier requires the Equipment Identifier (EID) of the DART 200 to give you an IP Address.

Ask your carrier for the following information:

• Side of their operation (A or B)

• IP Address

• IP Address of a router or server to ping when you are testing

Figure 1-2. CDPD network

M-ES

MAS/ CDPD Modem

Cellular Tower

CDPD network overview

The CDPD system is an extensive communications system overlaying the existing cellular voice network, as shown in Figure 1-2. It takes advantage of the investments already made by cellular providers. By adding CDPD to the network, packet data can be interspersed with voice communications at an advantageous cost to the end-user.

F-ES

MDBS MDIS

Public or Private Packet Data Networks

The communication flow sequence includes:

1. Data packets transmitted from the Mobile End Station (M-ES) are

received at the cellular towers by Mobile Data Base Stations (MDBSs)

Host System

2. Data packets are passed by the MDBS to the controlling Mobile Data

Intermediate System (MDIS)

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DART 200 CDPD Modem User’s Guide 1 Introduction

3. Data packets are routed by the MDIS through the appropriate

network to the Fixed End System (F-ES), usually a host computer over a public or private data network.

NOTE: Either the M-ES or F-ES can initiate CDPD communication.

4. If a response is required from the F-ES, the process is reversed. The role of the DART 200 in the CDPD network is to:

1. Accept commands and digital data from the end-user application

equipment through the RS-232 port.

2. Assemble the data into packets.

3. Encrypt the packets.

4. Transmit the encrypted data packet to the network. The DART 200 also:

1. Receives packet data from the network.

2. Decrypts the packets.

3. Disassembles the packets to extract the application data.

4. Passes the serial data to the end-user’s application equipment

through the RS-232 port.

Airlink security, to prevent eavesdropping, is provided by encrypting the data packets between the DART 200 and the MDIS. If end-to-end data security is desired it must be implemented or otherwise provided by the end-user.

The major cellular carriers and equipment manufacturers created a trade group called the Wireless Data Forum (formerly the CDPD Forum), that develops and publishes the governing technical specifications for, and promotes the use of CDPD technology.

AT command set summary

The Basic and Service Provider AT command sets are listed in Tables 1-1 and 1-2 (pp. 1-5 and 1-6). The AT commands can be concatenated (end-to-end or with a blank between commands) for up to a length of 80 characters including blanks, for example:

• Normal command concatenation

• ATE1V1&D0&S1\F3\N2

• AT\S?S57?&V+

• White space concatenation (for readability)

• AT E1 V1 &D0 &S1 \F3 \N2

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DART 200 CDPD Modem User’s Guide 1 Introduction

unexpected results.

Do not enter an AT command that requires a parameter without using one, as the missing parameter defaults to zero. For example, if you entered AT\N without a value in the range of 1 to 4, the command defaults to AT\N0. The \N0 setting also forces \J1, causing channel acquisition problems.

Similarly, the same thing can happen with concatenation. If you enter an invalid command, such as AT\N?, the DART 200 assumes a concatenation of AT\N and AT? The result is a display of the last register referenced (due to the AT?) and to set \Nn to \N0.

Use caution when entering commands. If you get unexpected results, display the register settings and modem profile with an AT&V command to check there is no entry error.

NOTE: Entering invalid AT commands can cause incorrect and

Table 1-1. Basic AT command set

A/ Repeat A Answer Online D Dial (connection setup) E Command Mode Echo F Online Mode Echo H Hang-up (close connection) I Identify O Enter Online Mode Q Quiet Mode S Select Register V Verbose Result Codes X Extended Result Codes Z Soft Reset ? Read Selected Register = Write Selected Register &C Set DCD Operation &D Set DTR Operation &E Escape Code Recognition On or Off &F Restore Factory Defaults &L Set DART Line Speed and Format &S Set DSR Operation &V View Active Profile &V+ View Radio Resource status &W Save Active Profile &Z Set or Display Dial Directory Entries \F Set Data Forwarding Operation \J Restrict Channel Selection \M Manual Transmit Control \N Set Side Preference \O Select PAD or Telnet Operating Mode \P Set, Enable or Disable PIN \Q Set Flow Control Operation \R Network Registration Control \S Set Subscriber Identity \T Automatic Transmit Control *A Select Server Type *B Enable/Disable Reception of Broadcast Messages

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Table 1-1. Basic AT command set (cont.)

*C Enable/Disable SLIP TCP Header Compression *E Enable Network Connection with PIN *G SLIP Multicast Address Selection *K TCP PAD Keep Alive *L Set Listen Port Number *M Set MAS IP Address for SLIP *P Ping Remote Host *R Automatic SLIP Restart *S Start SLIP (Serial Line IP) Mode *T Telnet Keep Alive *U Unblock Modem - Pin Access

Table 1-2. Service Provider AT command set

^A Set the IP Address of modem ^C Clear Blocked Status ^F Force PIN Usage ^G Set Multicast Group ID ^H Set Service Provider ID

^I Set Service Provider network ID ^L Set the Local Service Area ID ^P Enable/disable Supervisor Mode ^S Set the Modem SLIP Address

-L Set Channel Lock

-R Software Reboot

-V View Radio Resource Management Data

-Z View Modem Credentials

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2 Installation and Setup

Chapter

Field installation

Physical installation considerations

The Data Access Radio Transceiver (DART) 200 is designed for both stationary and mobile applications. The guidelines for modem

TIP: Use the optional mounting bracket to simplify the physical installation, refer to Figure C-1 for the mounting bracket template.

installation are:

• Environment - The standalone DART 200 is ruggedly constructed.

However, it is not waterproof, so do not locate the modem where it can get wet. Also, refer to the humidity specification in Appendix B, Product Specifications. If installing the DART 200 in a wet environment, enclose it in a proper National Electrical Manufacturer’s Association (NEMA) enclosure. Also, install the unit where there is adequate ventilation to prevent possible overheating

• Location - Installation with clear access to the unit is recommended

for viewing the LED, that indicates power and RF status, and for accessing the RS-232 port for required personalization or troubleshooting. Locate the DART 200, if possible, at least 2 feet from personnel

• Power Source - The DART 200 requires a nominal 13.8 V DC

regulated power source capable of supplying 2.5 amps maximum. Refer to Appendix B, Product Specifications, for more details. Wire the supplied power cord (Red positive, Black negative) with a Molex connector to the power source using a 3.0 amp fuse

• Refer to Figure 2-1 for instructions for installing the DART 200 with

the mounting bracket

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DART 200 CDPD Modem User’s Guide 2 Installation and Setup

Figure 2-1. Installing DART 200 with mounting bracket

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DART 200 CDPD Modem User’s Guide 2 Installation and Setup

Antenna considerations

The DART 200 uses standard mobile cellular radio signals and any standard cellular antenna of good quality with a maximum gain of 3 dB

NOTE: Snub-nosed (rubber duck) antennas, although they may work in some areas, are NOT recommended.

(FCC requirement) will function properly subject to the following guidelines:

• Location

Locate the antenna as far away from personnel as possible to minimize signal blocking. For optimum reception, in fixed location applications position the antenna above the height of personnel and

Operating the unit without an antenna does not damage the modem but can cause unpredictable results.

nearby equipment or structures. If used inside locate the antenna as close to a window as possible. In mobile applications, locate the antenna outside and away from or above any portion of the vehicle body that can block the RF signals. To determine the actual signal strength, attach a PC with an ASCII terminal emulator, such as Procomm, or Kermit, to view the Receive Signal Strength Indication (RSSI) value in S-Register 102.

• Antenna cable

Select an antenna cable with a low loss, high quality, 50 ohm, coaxial cable with the appropriate connectors. The cable can be any length, but lengths greater than 12 feet increase cable loss and offset

CAUTION: For outdoor fixed installations ground the antenna cable using an antenna discharge unit to prevent damage to the modem and the attached equipment.

the antenna’s nominal gain. If longer length cables are required, use a heavier wire gauge to reduce the dB loss/ft and to minimize the effect of the cable loss on antenna gain.

• Ground plane

For installations where a good antenna ground plane (metal surface) is not available, use a non-ground plane type of antenna to help maximize signal reception

• Proximity to other antennas

In general, do not locate the DART 200 and its antenna closer than five feet to another antenna; in certain cases, even more separation is required. In many vehicular applications, there are high-power two-way voice transmitters used and usually the antenna mounting locations are not five feet apart. The effect of the interference from the two-way transmitters varies from slowing down response times to blocking modem transmission.

In this situation, separate the antennas as far as possible and then do a test with the voice system also being used. If the DART 200 works satisfactorily you do not have an interference problem. If it does not work properly, then use filtering on the two-way output, the DART 200 input, or both. The calculation to determine the required filtering is not trivial and usually requires an RF engineer. However, if you do not have the option to do a test first, this analytical approach is your only option.

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DART 200 CDPD Modem User’s Guide 2 Installation and Setup

Troubleshooting

The DART 200 is thoroughly inspected during manufacturing. There are no end-user access items within the case of the modem. If problems

NOTE: To aid in troubleshooting use an IBM-compatible PC with an ASCII terminal emulator, such as Procomm, Terminal, Kermit, Hyperterminal, or a Mac with White Knight.

occur, check the following:

• Power supply

If the Power On/Registration Indicator is not flashing or glowing solid red, check the power source for adequate voltage. The modem requires regulated 12 V DC at 2.5 A. If the power is marginal it can be the problem. Check the fuse (if any) in the power source, and as a final test use a voltmeter to check for an open cable.

The DART 200 draws up to 2.5 amps under maximum power output. The power output is a function of the modem’s distance from the Mobile Data Base Station (MDBS). It is possible for the modem to work well with a particular power supply in a location requiring low power output (low current draw), and yet to fail using the same power supply in a location requiring a high power output. Check the amperage rating of the power supply to verify that it is adequate for all situations.

• Channel acquisition

If the modem does not acquire a CDPD channel (fast blinking or solid red light), refer to Channel acquisition, p. 2-10, for guidelines on how to proceed.

• Registration

If the modem does not register refer to Registration, p. 2-15, for guidelines on how to proceed.

• Unsuccessful data transfer

If the unit registered, but application data transfer is unsuccessful, check that the RS-232 cable is properly attached. If that does not correct the problem, substitute a good RS-232 cable (known to work). If that does not work, you may have a flow control problem. Refer to Flow control, p. 8-12, for guidelines. Also, review the Dial command (ATD) in Appendix F, DART AT Command Set, Auto Answer setup, p. 8-11, and Setup options, p. 5-17 or Basic UDP

setup options, p. 5-4, setup options as appropriate.

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DART 200 CDPD Modem User’s Guide 2 Installation and Setup

Getting started

Before opening the DART 200 box, but preferably before it arrives, check that the following equipment is available:

• A 12.0 V DC regulated power source with 2.5 amp capability. You

can either provide your own, or order the power source as an option with the DART 200

• A standard cellular antenna of good quality with a maximum gain of

3 dB. Cable attached magnetic mount antennas are preferred because the antenna can be positioned easily for optimum signal reception

• A PC with a communications program capable of operating in ASCII

terminal emulation mode. For IBM PC-compatibles this can be Procomm, Windows Terminal, Hyperterminal, Kermit or something similar

This makes the PC function as a terminal attached to the modem and permits the entering of AT commands required for both modem setup and diagnostics. It is recommended that the program chosen is capable of logging terminal communications activity to a file for later analysis or printout in the event that technical support is required

• A PC communications cable with a male DB9 connector. If your PC

has a DB25 communications port, get a DB25 to DB9 adapter (available from electronics stores)

Modem setup

To setup the DART 200:

1. Connect the antenna, PC, and power supply to the DART 200 using

appropriate cables and connectors. The red light on the end of the modem turns on and start blinking at a rate of approximately once per second (slow blink). If the light does not turn on, check the power source and connections.

The red OPR light doubles as a signal strength indicator. When the DART 200 finds a usable CDPD channel the rate of blinking increases in proportion to the strength of the received signal. This is discussed in more detail in Channel acquisition, p. 2-10.

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DART 200 CDPD Modem User’s Guide 2 Installation and Setup

2. To proceed, your PC must have the ASCII terminal emulation

program installed and active, and be attached to the CDPD modem by the PC communications cable. To verify the setup, enter AT and press ENTER: an OK response should return. To verify that the connection is with the DART 200 and not with an internal modem, enter ATI1 and press ENTER. If the response is the modem software version and date, proceed to Basic modem personalization. If you fail to get that response, verify that your cable is working and that the correct COM port is specified for the terminal emulation program and repeat this step.

3. If you still fail to get the AT echo and/or the OK, enter an AT&V

command to display the modems communications setup, profile, S-Registers and EID. The first three fields below the baud should be E1, V1 and Q0. If the values are anything else, change to the correct values and save the new values by entering ATE1V1Q0&W.

If the AT&V command fails, contact your DART 200 supplier for technical assistance.

Basic modem personalization

The DART 200 requires an IP Address to be set internally before it can be registered on the CDPD network. In addition, the side preference (A or B) for your carrier needs to be specified. This information can be preloaded by the carrier, but generally the carrier gives it to you upon request. To determine if the IP Address was preloaded, refer to step 1 (below). If the IP Address was not preloaded contact your carrier to obtain one along with the side preference (A or B), and a Domain Name Server (DNS) IP Address.

In addition to the side preference, the DART 200 has 23 additional operational parameters and several Status (S-)Registers to review. The default values for these parameters and S-Registers can require changes if they are not appropriate for your application. However, for initial setup the default parameters (except for side preference) are adequate.

To set up the DART 200 for operation:

1. Load the IP Address supplied by the carrier. To check if it was

preloaded, use the AT\S? command, as shown in this example:

at\s? * NEI 0 = IP ADDRESS 198.225.189.032 GMID 00000 OK

* - Means the Network Entity Identifier (NEI) is active

The DART 200 in the sample has the IP Addresses already entered. Ignore the Group Multicast Identifier (GMID) field for now.

If your modem has no IP Address, the response to the AT\S? command is OK. Enter the IP Address now, by:

• Putting the modem into Service Provider mode with an

AT^P+51348954 command

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DART 200 CDPD Modem User’s Guide 2 Installation and Setup

Current active profile

• Entering the IP Address with an AT^An.n.n.n. It defaults to

being put into the first entry in the IP Address table (NEI 0). For more information, refer to the AT^A command in Appendix F,

DART AT Command Set

• Verify that the IP Address was entered correctly using AT\S?

2. Examine the Modem Operational Parameters (Modem Profile). To

view these parameters, the communication port status and settings, and the DART 200’s S-Registers use the AT&V command, for example:

at&v

DART 200 Communication Port Settings: Auto Baud: 9600 Baud, 8 Data Bits, No Parity, 1 Stop Bit(s) E1 V1 Q0 F1 X1 &C1 &D0 &E1 &S0 \F3 \J0 \M0 \N3 \O1 \Q2 \T1 *A0 *B0 *C1 *G1 *K0 *R0 *T0

S00:000 S01:001 S02:043 S03:013 S04:010 S05:008 S06:127 S07:020 S08:250 S09:005 S10:080 S11:175 S12:050 S13:060 S14:074 S15:010 S16:050 S17:010 S18:010 S19:151 S20:000 S21:098 S22:016 S23:091 S24:140 S25:000 S26:003 S27:140 S28:140 S29:090 S30:010 S31:010 S32:005 S33:002 S34:001 S35:065 S36:041 S37:007 S38:003 S39:010 S40:090 S41:140 S42:080 S43:100 S44:023 S45:050 S46:005 S47:050 S48:050 S49:040 S50:020 S51:013 S52:026 S53:000 S54:000 S55:000 S56:000 S57:000 S58:058 S59:000 S60:001 S61:143 S62:000 S63:000 S64:022 S65:003 S66:002 S67:020 S68:020 S69:108 S70:010 S71:006 S72:005 S73:005 S74:006 S75:008 S76:240 S77:030 S78:000 S79:001 S80:250 S81:017 S82:002 S83:030 S84:000 S85:000 S86:120 S87:000 S88:020 S89:010 S90:008 S91:003 S92:000 S93:000 S94:000 S95:011 S96:000 S97:002 S98:090 S99:008 EID: 0020EB000B71

(factory defaults)

Most S-Registers are used by the DART control program. The S-Registers of interest to the end-user are discussed in the following sections.

3. Set Side Preference with AT\Nn. This command specifies which

service provider side (A or B) to search for a usable CDPD channel. In each geographical area, there is a maximum of two service providers (an A side carrier and a B side carrier). Your carrier sets up this value or provides you with their preference. The default is \N3 (A side preferred), but is not appropriate for most end-users. If you have an A side carrier, enter AT\N1; if the carrier is B side enter

AT\N2.

4. Verify that there are no channel restrictions in place. These

restrictions are controlled by the \Jn parameter. The default value is \J0, no restrictions, and is the desired setting. If this parameter has a non-zero value from prior use, set it to zero with AT\J0 before proceeding.

5. Save your changes into permanent memory with the AT&W

command. Issue this command after making the above changes to ensure that new values replace the default values.

6. Display the modem profile using the AT&V command to check that

your change to the \N parameter was successful.

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The basic setup for your CDPD modem is now complete.

DART 200 CDPD Modem User’s Guide 2 Installation and Setup

Selecting CDPD 1.0 or 1.1 mode of operation

DART firmware Version 3.0.1 and above can operate in either CDPD 1.0 or 1.1 mode; prior firmware versions support only CDPD 1.0. The firmware version can be determined by the ATI1 command.

The default is to operate in CDPD 1.1 mode, but in areas where CDPD

1.1 is not yet active, the operating mode can be changed to CDPD 1.0. To set CDPD 1.0 mode, set S-Register 95 to 8 (default is 11) as follows:

1. Enter Service Provider mode with AT^P+51348954.

2. Set S-Register 95 for CDPD 1.0 mode with ATS95=8.

3. Save change with AT&W.

4. Restart to activate the change with AT-R. To change back to CDPD 1.1 mode, repeat steps 1 to 4, but set

S-Register 95 to 11 instead of 8.

Initial testing

Setup verification

The first step to make the DART 200 operational is to verify the setup by doing the following:

1. Use AT\S? to view and verify the IP Addresses, for example:

at\s? * NEI 0 = IP ADDRESS 198.225.189.032 GMID 00000 OK

* Means the NEI is active

If you are just starting, there should be no problem here, because the IP Address was just entered. However, if the address needs correction, put the modem into Service Provider mode with an

AT^P+51348954 command, then enter the IP Address with an AT^An.n.n.n.

The GMID is used with multicast operation, the value now should be zero.

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DART 200 CDPD Modem User’s Guide 2 Installation and Setup

wide use.

2. If the NEI information is correct, use AT&V to verify the side

setting (\Nn) and channel restrictions (\Jn), for example:

ar&v

DART 200 Communication Port Settings: Auto Baud: 9600 Baud, 8 Data Bits, No Parity, 1 Stop Bit(s) E1 V1 Q0 F1 X1 &C1 &D0 &E1 &S0 \F3 \J0 \M0 \N3 \O0 \Q2 \T1 *A0 *B0 *C0 *G1 *K0 *R0 *T0 S00:000 S01:001 S02:043 S03:013 S04:010 S05:008 S06:127 S07:020 S08:250 S09:005 S10:080 S11:175 S12:050 S13:060 S14:074 S15:010 S16:050 S17:010 S18:010 S19:151 S20:000 S21:098 S22:016 S23:091 S24:140 S25:000 S26:003 S27:140 S28:140 S29:090 S30:010 S31:010 S32:005 S33:002 S34:001 S35:065 S36:041 S37:007 S38:003 S39:010 S40:090 S41:140 S42:080 S43:100 S44:023 S45:050 S46:005 S47:050 S48:050 S49:040 S50:020 S51:013 S52:026 S53:000 S54:000 S55:000 S56:000 S57:000 S58:058 S59:000 S60:001 S61:143 S62:000 S63:000 S64:022 S65:003 S66:002 S67:020 S68:020 S69:108 S70:010 S71:006 S72:005 S73:005 S74:006 S75:008 S76:240 S77:030 S78:000 S79:001 S80:250 S81:017 S82:002 S83:030 S84:000 S85:000 S86:120 S87:000 S88:020 S89:010 S90:008 S91:003 S92:000 S93:000 S94:000 S95:011 S96:000 S97:002 S98:090 S99:008

EID: 0020EB000B71

NOTE: The bits are numbered in high to low order from left to right that is the reverse of some notation systems in

If this is the initial setup, the only parameter that changed from the default value is the side preference specification (\N). Verify that it is set to match your carrier before proceeding. Refer to Basic modem personalization, p. 2-6, for details.

3. If the modem has been used previously, then some of the profile

parameters and S-Registers might be altered. Check that the profile is correct before proceeding to step 4.

4. If you made changes, save the new configuration with the AT&W

command before continuing.

The DART 200 keeps its status and control information in S-Registers. Many of its functions are controlled by bits within a register, and are displayed as a numerical value. Figure 2-2 shows the register notation used.

Figure 2-2. S-Register bit positions

S-Register

Bit Position 7 6 5 4 3 2 1 0

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The values associated with the bit positions are listed below.

Bit Position Value

0 1 1 2 2 4 3 8 4 16 5 32 6 64 7 128

For example, if register bits 0,3, and 5 are on, the register value would be 1+8+32=41.

Channel acquisition

For the DART 200 to acquire a channel for operation it must have a good antenna and an MDBS near enough to deliver a signal that is strong enough to be received by the modem. CDPD systems are currently defined as being either forced hopping or dedicated.

In a forced hopping (often called sniff-and-hop) system, an MDBS has multiple channels (from 1 to 21, but usually 7) shared by voice calls or CDPD. CDPD uses any available channel when it is not in use for voice. If a voice call wants a channel already in use for CDPD, the MDBS notes that occurrence (sniffs) and moves CDPD to another available channel (hops).

The modem detects the fact that the current channel no longer supports CDPD (loss of sync), and searches for an alternate CDPD channel using the MDBS’s adjacent channel list. In such a system, CDPD operates in the time between voice calls. During busy periods there is little time available. Applications requiring quick response times are adversely affected by the hopping.

In a dedicated system, each MDBS has one or possibly two channels assigned for CDPD use only. In such a system, contention with voice calls is not an issue and application response times are much more predictable.

• CDPD Version 1.0 Mode Operation

In the above system types, the channel acquisition process is:

1. The DART 200 powers up and immediately begins searching for

a CDPD channel to use. It searches sequentially, from the lowest numbered channel to the highest, on the side (A or B) it is configured to use, starting at a relatively strong signal level (-60 dBm).

2. Each time the DART finds an active channel, the modem checks

to determine if it is in use for voice or available for CDPD.

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DART 200 CDPD Modem User’s Guide 2 Installation and Setup

3. If the channel is not available for CDPD use, the DART

continues searching, dropping the allowable signal level by 10 dB after each pass through all the cellular channels on the side it is searching, until it finds a usable channel or reaches the weakest allowable signal level (-110 dBm).

4. If an available CDPD channel was not found, the search starts

over again at -60 dBm and the modem repeats the spiral search process indefinitely until an available CDPD channel is found.

5. When a CDPD channel is found the modem checks that the

block error rate (BLER) is acceptable.

6. If the BLER is adequate, the DART extracts the network

operating parameters (continuously being broadcast by the MDBS) from the data stream, then stays on the channel as long as possible awaiting commands from the Mobile Application Subsystem (MAS); the attached device. If the BLER is not acceptable the search continues.

7. While on the CDPD channel, the modem accepts operating

parameters (called XID parameters) broadcast by the base station, including thresholds, threshold time limits, and adjacent channel lists. The modem continually monitors its radio environment and compares the current signal quality to the thresholds and time limits; if any of the thresholds are exceeded for longer than their permissible time limit, the modem must go find a better channel. To speed up this search the modem makes use of the adjacent channel lists picked up from the base station along with the operating parameters.

This process allows a modem to stay on an acquired channel, until the signal strength or BLER fails the threshold test. In a situation where the M-ES is mobile, the modem can continue to use a channel far from its original acquisition point (a phenomenon known as cell dragging). In many cases this causes interference with voice channels on intervening base stations. One of CDPD Version 1.1’s main objectives is to avoid cell dragging.

• CDPD Version 1.1 mode operation

In the system types already described the channel acquisition process is:

1. The DART 200 powers up and immediately searches for a

CDPD channel to use. It searches sequentially, from the lowest number channel to the highest, on the side (A or B) it is configured to use recording the signal strength (RSSI) of every active cellular channel encountered.

2. The DART then sorts the channels in descending order of

strength and evaluates them to find the best available (strongest signal) CDPD channel (in a dedicated system many in the list are voice only channels).

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3. If the CDPD channel’s BLER is acceptable, the DART acquires

the power product, current CDPD operating parameters, and adjacent channel lists from the MDBS. If the channel BLER is not satisfactory, the modem goes to the next best CDPD channel in the list and repeats this step using the next best channel.

4. Once a channel is acquired, there is no guarantee that the modem

stays there very long. In a sniff-and-hop system it is forced to continuously hop from one channel to another because voice traffic has priority. Even in a dedicated system, if the modem is mobile, it is forced to frequently change channels as it travels from one cell coverage area to another.

5. The XID parameters broadcast by the base station, in addition to

the thresholds, threshold time limits, and adjacent channel lists used with CDPD 1.0, include an evaluation frequency (scan time), and a signal strength change (scan delta) value. As in CDPD 1.0 mode, the modem continually monitors its radio environment and compares the current BLER value to the XID threshold and time limit; if the threshold is exceeded for longer than the permissible time limit, the modem finds a better channel. To speed up this search, the modem makes use of the adjacent channel lists picked up from the base station along with the operating parameters.

CDPD Version 1.1 requires that the DART periodically evaluates alternative channels to ensure that it is still operating on the best available channel. Also, CDPD Version 1.1 requires that if the DART detects an RSSI changes of more than a predetermined amount, from the initial acquisition value, it must check that it is still using the strongest channel in the area. These features, scan time (usually 90 seconds), and scan delta (usually +/- 8 dB), help to keep the M-ES on the best available channel, and avoids the cell dragging phenomenon common to mobile M-ESs operating in CDPD 1.0 mode.

Whenever the RSSI threshold or scan delta is exceeded, or the scan timer expires the modem must locate a better channel if possible. To speed up this search, the modem makes use of the adjacent channel lists picked up from the base station along with the operating parameters.

Problem determination

There are three ways to determine if a channel was acquired:

• By observing the OPR light (simplest way). At power on this light

flashes at the rate of about once per second. When the DART 200 acquires a channel the rate of flashing speeds up to at least twice per second and flashes faster as the signal strength increases. A very strong signal causes the light to glow steadily

• By viewing S-Register 101 with the ATS101? command. A value of

1 indicates that a channel has been acquired

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DART 200 CDPD Modem User’s Guide 2 Installation and Setup

• By viewing the Network Status Register (S-Register 57) with the

AT&V command or the ATS57? command. This is the recommended method, because viewing S-Register 57 shows other useful information, as shown in Figure 2-3

Figure 2-3. Viewing the network S-Register (S57)

ATS57?

160

A value of 128 (bit 7 on) or higher indicates that the modem acquired a channel. If auto-registration at power on (AT\R4) is specified, then the value is 160 (bits 5 and 7 on) or 161 (bit 0 also on) indicating that it completed registration.

If the DART cannot acquire a channel, move the antenna to a better location. To determine the best location for the antenna you need some indication of received signal strength. This is given by the RSSI; one of the radio resource values. View RSSI with the ATS102? or the AT&V+ command.

Figure 2-4 is a snapshot of the CDPD channel at a specific point in time. View this data several times to see if the modem is staying on a single channel (S-Register 100) or continues to search. If the value in S-Register 101 is a zero, then the search is continuing.

Figure 2-4. Monitoring the CDPD channel

at&v+

DART 200 S100:00799 S101:00001 S102:-0073 S103:00002 S104:00040 S105:00000 S106:00001 S107:00000 S108:00022 S109:00010 S110:00079 S111:00001 S112:00000 S113:00000 S114:00000 S115:00000 S116:00000 S117:00000 S118:00018 S119:0FFFF S120:00000 S121:00002 S122:00000 S123:00002 S124:00030 S125:14400 S126:00005

If the modem cannot acquire a usable channel (S-Register 101 = 1) after a few minutes there are several possible causes:

• The signal strength is too weak

• The cell is not currently CDPD capable (check with your cellular

carrier)

• The modem has an incorrect channel restriction configuration. Use

the AT&V command to check the \Jn setting

• The side setting is wrong. Use the AT&V command to check the

\Nn setting

• There is an interference problem

• The modem is faulty

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If the problem persists after checking the above possibilities, try power cycling the modem. If that fails to help, contact your modem supplier for assistance.

To determine if you have a channel restriction problem check the setting of the \J parameter with an AT&V. If it is \J0 then the DART 200 has no channel restrictions, so this can be eliminated as a possible source of the problem. If \J has any other value then bypass the problem by entering the AT\J0 command followed by an AT&W.

The S-Registers of interest in the AT&V+ output are summarized in Table 2-1. The remainder of S-Registers are described in Appendix E,

S-Registers.

Table 2-1. S-Registers above 100

S100 The channel currently being reported (may not be acquired) S101 Will be 1 if a channel has been acquired S102 RSSI for the channel being reported S103 Output power (0 to 7 with 0 being highest and 7 lowest) S104 MDBS power product (a request for a specific power output) S105 Current BLER (receive block error rate - %) S106 Current SER (symbol error rate - %) S107 Current LSAI (CDPD V1.0), or WASI (CDPD V1.1) S108 Current SPNI (service provider network identifier) S109 Current CSI (channel stream identifier) S110 Current LCI (local cell identifier) S111 Current Area/Cell color code S112 Current TX BLER (transmit block error rate - %) S113 Current SIE (symbols in error) S114 Current SPI (Service Provider ID) (CDPD V1.1)

XID RSSI threshold, time (CDPD V1.0) * threshold is dBw above -143 (in this case -125); * time (in 1/10 sec) is how long RSSI can be below threshold before a channel hop must be taken (5 seconds in this case)

S115 Not Used (CDPD V1.1)

XID BLER threshold, time (CDPD V1.0) * Block error rate threshold (1/n) in % (10% in this case) * time (in 1/10 sec) is how long BLER can be above threshold before a channel hop must be taken (1 second in this case)

S116 Not Used (CDPD V1.1)

XID SER threshold, time (CDPD V1.0) * Symbol error rate threshold (1/n) in % (10% in this case) * time (in 1/10 sec) is how long RSSI can be below threshold before a channel hop must be taken (5 seconds in this case)

S117 Reserved S118 Reserved ~ ~ ~ ~ ~ ~ S126 Registration progress counter

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DART 200 CDPD Modem User’s Guide 2 Installation and Setup

If the modem stabilizes for short periods before restarting the search, the AT&V+ output shown in Table 2-1 can be useful.

S-Register 102 contains the RSSI value in dBm. The less negative the number the stronger the signal, for example, for CDPD 1.1:

• Strong signals are in the range of -45 to -59

• Good signals are in the range of -60 to -74

• Acceptable signals are in the range of -75 to -89

• Weak signals are in the range of -90 to -104

• Signals below -100 are usually not dependable and can prevent the

modem from acquiring the channel

Sometimes local radio interference prevents channel acquisition. If the BLER in S-Register 105 is above 10%, this could be the problem. Try moving the antenna as far as possible from its current location or, if possible, move to another location to determine if the problem can be lessened.

CAUTION: With auto-registration active the DART can lock up, requiring a power cycle to clear it, if manual registration (AT\R1) is attempted and the registration fails to complete successfully.

Before deciding that the location is unsuitable, execute the AT&V command and examine S-Register 60. If the 2 bit is on (usually a 5), then the modem was set up to suppress channel searching, probably for use at a trade show. Reset S-Register 60 to the default value of 1 with an ATS60=1 command, and save it with an AT&W command. If this was not the problem, contact your carrier to discuss the lack of CDPD coverage.

Registration

Once the DART 200 acquires a channel the next step in the initial operation process is registration; performed by the AT\R command.

The first few times you register the modem use manual registration (AT\R1), to get a feel for timing, and from the timing an indication of potential problems. When registration becomes routine use continuous auto-registration (an AT\R4 command) combined with an ATS13=0 command. Save these changes with an AT&W command, and activate the changes by power cycling or restarting (AT-R) the modem.

This setup causes the modem to attempt to register at power on and whenever the modem loses registration, for example, when driving out of coverage. Registration status can be viewed by using the ATS57? command, as shown in Figure 2-5.

Figure 2-5. Viewing registration status with ATS57?

ATS57?

161 (bits 7, 5, and 1 are on)

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The bit definitions in Figure 2-5 are as follows:

• Channel acquired indicator (bit 7)

• Automatic registration switch (bit 5)

• Registration indicator (bit 0)

An odd value in S-Register 57 indicates a registered modem. If the DART has problems registering, begin problem determination by

checking the contents of S-Register 56 with the ATS56? command. The

NOTE: Most carriers and equipment manufacturers follow these guidelines making problem determination easier. If these guidelines are not followed, more ingenuity is required.

possible return codes are listed below:

• S-Register 56 Return Codes

Return codes 0 through 7 are suggested by the CDPD specification. 0 Reset condition - Also, registration is incomplete but did

not time out. Refer to the description of S-Register 126 in the next bullet point for details

1 Registration denied - Usually means IP Address is being

used by another device. On some systems it could also be an invalid NEI or a credentials mismatch

2 Service currently unavailable 3 Invalid NEI (IP Address) 4 Insufficient authentication credentials 5 Unsupported authentication credentials 6 NEI has exceeded usage limitations 7 Service denied on this subnetwork - service can be obtained

on an alternate Service Provider network

250 Timer expired waiting for the home MDIS Intermediate

System Confirmation (ISC) registration response - Usually caused by router problems between the home and serving MDISs

251 MDLP parameters unsupported 252 MDLP version unsupported 254 Could not access the CDPD network 255 Could not de-register because M-ES was not registered

• S-Register 126 - Registration Progress Indicator

CDPD registration is a four-step process that can, if there are problems anywhere in the system, be delayed or halted at any of the steps. If your registration attempt is unsuccessful, use ATS126? to view S-Register 126 to determine at what step in the registration process progress halted.

0 Protocol not active 1 Waiting for Temporary Equipment Identifier (TEI) assignment

from MDIS

2 Link connection establishment pending - waiting for the

Unnumbered Acknowledgement (UA) from MDIS

3 Encryption key exchange pending - waiting for MDIS Key

Exchange (IKE) from MDIS

4 Registration pending - End System Hello (ESH) sent, waiting for

Intermediate System Confirmation (ISC) from MDIS

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5 NEI successfully registered The descriptions of S-Registers 56 and 126 usually give a good idea

of what the problem is. The following section describes some of the most common conditions leading to registration failures.

Troubleshooting registration failure

The most common conditions leading to registration failures and possible solutions are listed in Table 2-2. If your problem does not appear in Table 2-2, or if after checking the conditions you cannot find the problem, contact your carrier for assistance. If your carrier cannot find the problem, then contact the modem supplier for guidance

Table 2-2. Registration failure troubleshooting

Condition Result

Code

Weak signal strength

Wrong side specified

0 or 254 1. Verify that the RSSI is adequate. Refer

3 (invalid NEI)

Solution

to Channel acquisition, p. 2- 10, for instructions.

2. If you are mobile, the signal could be

temporarily out of range. If you are stationary, you could be in a marginal reception area. If you are stationary and have a magnetic mount antenna, relocate the antenna while observing S-Register 102. The objective is to get a less negative value.

3. If this does not improve the signal, or

if you are mobile use a better (higher gain) antenna. Do not use an antenna with gain greater than the FCC allowed maximum of 3 dB.

Check that you are operating on the same side (channel range) as your carrier, because if there are two CDPD carriers in your area you may have acquired a channel on the wrong system.

1. Use the AT&V command to view the \Nn parameter, where n specifies which side (1 = A side, 2 = B side) you are operating on.

2. Correct the side setting, if necessary.

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Table 2-2. Registration failure troubleshooting (cont.)

Condition Result

Code

Invalid IP Address

3 or 1 (on some systems)

Expired IP

6 As CDPD networks grow, some carriers

Address

Solution

1. If the side setting is OK, verify that the modem’s IP Address is correct, by using the AT\S? command to view the IP Address. If the modem has more than one IP Address in the table, verify that the active NEI, the one with the asterisk (*) to the left, is correct. This condition could also mean that the carrier did not activate this IP Address.

2. Contact the carrier to ensure that the IP Address is valid and active

are concerned about unauthorized use of unused IP Addresses to gain access to the network. To minimize this likelihood an expiration time is used, usually a few hours long, on each new IP Address. If you are slow in registering a modem with a recently assigned IP Address, the expiration time period can be exceeded. Find out from your carrier if they employ this strategy, and if so register new IP Addresses promptly.

Authentication (credentials) problem

4 or 5 Each IP Address has two credential values

associated with it: a sequential number and a random number. These numbers are initially set to zero at the MDIS when the IP Address is assigned to an end-user. When the end-user puts the IP Address into the modem these values are also set to zero.

When the IP Address is registered, these values are compared at the MDIS to ensure that they match. If they do, a new random number is generated at the MDIS and returned to the modem, and both ends update their sequential numbers. On each subsequent registration these values are compared by the MDIS (before updating) to see that they match. The modem keeps these credentials separately for each slot in the NEI (IP Address) list.

Problems can arise if the IP Address is reloaded after it was registered, or is being reused or shared among modems. Any of these activities will cause the modem

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Table 2-2. Registration failure troubleshooting (cont.)

Condition Result

Code

Authentication (credentials) problem (cont.)

Flow control problem

Not applicable

Solution

credentials to be reset. Trying to register a modem after doing this will cause a credentials error because the reset values in the modem do not match the values the MDIS has for that IP Address from prior usage.

This problem is not likely when you are initially registering a new modem, unless the IP Address was previously used in your organization. If a credentials problem is indicated, contact the carrier to have the credentials for the IP Address reset.

If you suspect that this occurred, use the AT-Z command (in service provider mode) to view the actual credentials. If the displayed credentials are zero, call the carrier to get the IP Address reset.

This condition is only possible if you are using manual registration (AT\R1) instead of automatic registration. If, after you key AT\R1 and press ENTER, the cursor returns to the A of the AT and the modem does not return an OK or an ERROR within the time-out period (S-Register 13) you likely have this problem.

Flow control is only applied when the modem is in online mode or is interacting with the network in command mode (as it is when trying to register). Even if the flow control is set improperly, or has a cable problem that impacts flow control, you will not notice it until you try to register. The flow control setting defaults to hardware flow control, indicated by \Q2 in the modem profile, and this should match the COM port setting on your PC’s terminal emulator program. If the settings match try changing them both to no flow control (\Q0) on the DART. If registration now works then a broken or missing pin, faulty connection, or broken or missing RTS or CTS wire is the likely source of the problem.

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Table 2-2. Registration failure troubleshooting (cont.)

Condition Result

Code

Power supply problem

MDIS or network

Not applicable

251, or 252 in S-Register 56

problem

Solution

The DART operates on a voltage of 11 to 16 VDC with a current rating of 2.5 amps. Voltage level fluctuations caused by using an unregulated power supply, or a supply with too low a current rating will cause the modem to experience a power reset. This forces the modem to reset itself before it can complete the multi-step registration request.

The most frequent problem is too low a current rating. The MDBS controls the output power of the DART. The DART may work well with a particular power supply in a location where low power output is required, and yet fail using the same power supply in a different location if the power output demands are higher.

Use a power supply with an amperage rating of at least 2.5 amps to avoid this problem.

Registration problems can be caused by the MDIS, or by the network beyond. If you are operating in an area where CDPD service is new or has recently had software changes then this is a possibility.

250 in S-Register 56

If your serving MDIS is different than your home MDIS (usually occurs if the F-ES is in one carrier’s territory and the DART is registered on a different carrier’s MDIS) a network router or link problem could cause the registration attempt to time out.

1. View S-Register 126 to determine how far through the registration process the modem had progressed. Home MDIS delay problems show up as 4 in this register.

2. Contact your local carrier for assistance

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DART 200 CDPD Modem User’s Guide 2 Installation and Setup

Basic communications

The final step in the initial setup process is to confirm that the DART 200 can communicate with the network by performing a ping. The DART 200 sends a fixed length character string to another device that is registered on the network, and requests that it be echoed back. However, to do a ping you need the address of another registered device.

Get two addresses to ping: a network server or Domain Name Server (DNS), and a second DART adjacent to the first. Get the IP Address of a network server or DNS from your carrier at the same time you get your IP Address assigned. If you can ping the server or DNS, basic connectivity is functional. If you can ping a device, such as a second DART, on the other side of the MDIS, then network connectivity is established.

Ping is executed by the AT*P command, as shown in this example:

at*p198.225.191.25

Press <ENTER> to stop PING Host (198.225.191.25): 60 data bytes & 8 header bytes

68 bytes from 198.225.191.25: icmp_sn=0. time=1380. ms TSR=7631.250S 68 bytes from 198.225.191.25: icmp_sn=1. time=920. ms TSR=7632.280S 68 bytes from 198.225.191.25: icmp_sn=2. time=790. ms TSR=7633.180S 68 bytes from 198.225.191.25: icmp_sn=3. time=1340. ms TSR=7634.620S 68 bytes from 198.225.191.25: icmp_sn=4. time=1440. ms TSR=7639.660S 68 bytes from 198.225.191.25: icmp_sn=8. time=860. ms TSR=7636.180S 68 bytes from 198.225.191.25: icmp_sn=5. time=1450. ms TSR=7637.730S 68 bytes from 198.225.191.25: icmp_sn=6. time=900. ms TSR=7638.740S 68 bytes from 198.225.191.25: icmp_sn=7. time=820. ms TSR=7640.620S

----198.225.191.25 PING Statistics---10 packets transmitted, 10 packets received, 0% packet loss 0 sequence errors round-trip (ms) min/avg/max = 790/1127/1450

The ping executes continuously until the <CR> key is pushed. The ping command is covered in detail in Appendix F, DART AT Command Set.

If the network server and another device were successfully pinged, the initial operation is complete and you are ready to begin application testing.

The time since reset (TSR) field represents the time in seconds since the modem was last reset (through an AT-R command or a power cycle). Problems with the ping are usually seen as time-outs. Most devices respond in less than 2 seconds using the default ping packet size. Both packet size (60 bytes plus an 8 byte header) and the time-out period (default is 10 seconds) are in S-Registers 71 and 70 and can be changed. If you increase the size of the packet, consider increasing the time-out period to allow for the longer transit time of the larger packet.

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If increasing the time-out period does not correct the time-out failures, the problem could be that the other device is not registered, or that the path to it is not operational. Check with those responsible for the other device to see that it is operational and registered. Next, check S-Register 57 to see if you have a channel and are still registered. If you are, then verify that the IP Address of the ping target is correct. If S-Register 57 status is fine and the IP Address is also fine, contact your carrier to check for network connectivity between the local modem and remote device.

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3 CDPD Security Features

Chapter

Airlink security

The Cellular Digital Packet Data (CDPD) network is a public wireless data communications service vulnerable to casual eavesdropping. To minimize this possibility, a data encryption mechanism is provided for all non-broadcast communications between the Mobile Data Intermediate System (MDIS) and the Mobile End System (M-ES).

If activated by the carrier, encryption services are implemented by the MDIS. At registration time the Data Access Radio Transmitter (DART) 200 is told, during session negotiation, whether or not encryption is being used. The M-ES has no choice and follows the lead of the MDIS in using or not using encryption

Authentication services

M-ES authentication is provided within the CDPD network to prevent fraudulent use of the network. This mechanism is implemented by the MDIS, as follows:

1. The MDIS validates the Authentication Data (credentials) presented

by the M-ES at registration time by comparing them against information stored in the MDIS authentication table.

2. If the credentials are acceptable to the MDIS they are updated, stored

back into the MDIS authentication table, and also sent back to the M-ES for use when it next registers. Registration is denied if the M-ES presented credentials do not match those stored for its Network Entity Identifier (NEI) by the MDIS.

When an IP Address is first authorized for use by the carrier, or an IP Address is loaded into a modem, the associated credentials are set to zero. On each subsequent registration the credentials are for the IP Address are updated as described in steps 1 and 2 above.

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DART 200 CDPD Modem User’s Guide 3 CPDP Security Features

Modem security management

Two types of modem security are provided for the DART 200:

• Personal Identification Number (PIN) - Protects against unauthorized

use of the CDPD network. A PIN can be required before the modem can gain access to the CDPD network

• Service Provider Key (SPK) - Protects against modem operating

parameters being altered. An SPK is mandatory before making changes

The use of the PIN can be required by the service provider, although currently none do. If not required by the carrier, you have the option of requiring it, or leaving it disabled (this is the modem default). However, the use of the SPK is mandatory and cannot be disabled.

The intent of the security management feature is to provide a layer of control at the end-user level, in addition to CDPD network authentication services, to aid in the prevention of unauthorized access to the network.

Table 3-1 summarizes the DART 200’s PIN management system. There are four keys and six AT commands, three of which will only function when in service provider mode, involved in the total process.

Table 3-1. Key types

Key Description

PIN Prevents unauthorized access to the CDPD network by

blocking commands that access the network, including the registration command (AT\R) and the dial command (ATD). To use these commands an authorized PIN and the AT*E command are required. If the PIN is entered incorrectly three times in a row it becomes BLOCKED. The default is PIN not required.

PIN Unblocking Key

The AT*U command temporarily enables the PIN when it becomes BLOCKED, allowing it to reset or change to a new value. BLOCKED status is permanently cleared by the AT^C command, and PIN values are reset or changed by the AT\P command. If the PIN unblocking key is entered incorrectly 10 times in a row, it also becomes BLOCKED. The BLOCK of the PIN Unblocking Key is also cleared by the AT^C command.

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Table 3-1. Key types (cont.)

SPK Prevents unauthorized changes to the modems operating

parameters. These include selected S-Registers as well as modem IP Addresses. In addition, the use of selected AT commands, including several of the security management commands, is also controlled by this key. This key is enabled by the AT^P command. If entered incorrectly three times in a row, it will become BLOCKED.

When the SPK is in the BLOCKED state, entering any SPK through the AT^P command causes a 30-second delay before the BLOCKED response is returned. This delay imposes a barrier to computer-generated attempts at finding the Master Key value by unauthorized users.

Master Key Temporarily enables the SPK when it becomes BLOCKED

allowing the BLOCKED status to be cleared. Temporary unblocking is performed by the AT^P command, and the BLOCKED status is permanently cleared by the AT^C command. The Master Key cannot become BLOCKED.

AT Commands

The AT commands used to implement the security management feature (*E, \P, ^F, *U, ^P, ^C) and the default keys are described in detail in Appendix F, DART AT

Command Set.

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4 Broadcast and Multicast

Operation

Overview

Broadcast and multicast are Cellular Digital Packet Data (CDPD) functions that support sending the same data to a large group of IP Addresses with a single transmission to the CDPD network. This capability is implemented through Mobile Data Intermediate System (MDIS) software.

The facility was originally defined for Fixed End System (F-ES) (host) to Mobile End System (M-ES) (terminal) transmissions. However, some MDIS manufacturers have implemented multicast to also support M-ES to M-ES transmissions. Protocol restrictions prevent broadcast or multicast messages from being encrypted. Check with your carrier to determine if these capabilities are offered before planning to use it as part of your application.

Broadcast and multicast transmissions are point-to-multi-point and provide a one-way connectionless service. The protocol used is User Datagram Protocol (UDP) or another unacknowledged protocol that operates over IP, for example, ICMP PING. The operational considerations are:

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1. Broadcast or multicast data packets will not be received by a DART

200 with an active telnet or Transmission Control Protocol (TCP) PAD session.

2. If a User Datagram Protocol (UDP) PAD session is active the

broadcast and multicast messages will be interspersed with the application data packets and must be separated by the application.

3. In the case of Serial Line Internet Protocol (SLIP), the disposition of

the broadcast and multicast messages is a function of the support provided by the software stack and end-user applications (one must be UDP) operating on the Mobile Application Subsystem (MAS). If a UDP session is not active, the messages will be lost.

DART 200 CDPD Modem User’s Guide 4 Broadcast and Multicast Operation

Broadcast

The Broadcast function is used on a geographic coverage basis. To support this function the MDIS is set up with a Broadcast Network Entity Identifier (NEI) that includes a list of the Mobile Data Base Stations (MDBSs) in the desired broadcast area in its definition. There can be multiple broadcast areas within the coverage area of a single MDIS. The message is sent (by the F-ES or an M-ES) to a Broadcast NEI at the MDIS that replicates the message, puts a special broadcast header on it, and sends it to the cells indicated by the broadcast list.

Any Data Access Radio Transmitter (DART) wishing to receive broadcast messages indicates its readiness by having specified the *B1 profile parameter and by being ready to receive UDP datagrams. The latter can be accomplished by having the UDP Server function active or, if in SLIP mode, by having a Winsock UDP application active, and by being ready to process any incoming broadcast datagrams.

For most applications broadcast is not appropriate, because broadcast messages are sent to all the CDPD modems in the covered geography. It is more useful to be able to specify that messages only go to all, or a subset of the IP Addresses associated with a specific customer; a capability offered by multicast.

Multicast

Multicast is set up similarly to broadcast, except that the MDIS is set up with a Multicast NEI and a list of the M-ESs that belong to that specific group rather than a list of cells, as is done by the broadcast function. The message to be multicast is sent (by the F-ES or an M-ES) to the Multicast NEI at the MDIS, that replicates the message and sends individual messages to the M-ESs indicated in its multicast group list.

An M-ES can be a member of any number of multicast groups, however it can only be active in one at any given time. An M-ES wishing to receive multicast messages indicates its readiness by registering a Multicast NEI and by being ready to receive UDP datagrams. The latter can be accomplished by having the UDP Server function active, or if in SLIP mode, by having a UDP application ready. In all of the preceding cases the MAS is assumed to be ready to process any incoming multicast datagrams.

Contact your service provider for information on the availability and use of multicast service in your area.

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Multicast setup

For multicast set up the DART 200 with a multicast IP Address and an associated Group Multicast Identifier (GMID), in addition to the normal IP Address, as follows:

1. Enter the Multicast NEI (like any other IP Address) by using the

AT^A command.

2. Select the NEI for multicast use with the AT\S+n command, where

n is the slot number in the DART 200’s IP Address list.

3. Define the GMID, use the AT^G command that assigns a multicast

group ID to the slot containing the Multicast NEI, for example:

• AT^P+51348954 Must be in Service Provider mode

• AT^A198.225.189.35/1 Enter multicast IP Address in slot 1

• AT^G12/1 Set GMID for slot 1 to 12

• AT\S+1 Select IP Address in slot 1 for

multicast use

4. Verify the set up of your Multicast NEI with an AT\S? command; it

shows the CDPD modem’s NEI status. The screen appears as shown in Figure 4-1:

Figure 4-1. Checking NEI status with AT\S?

AT\S?

SLIP = IP ADDRESS 001.001.001.002 MAS = IP ADDRESS 198.225.189.031

* NEI 0 = IP ADDRESS 198.225.189.031 GMID 0000C + NEI 1 = IP ADRESS 198.225.189.035 GMID 00012

SPI 0 = 00012 SPNI 0 = 00035 WASI 0 = 00001

* - Indicates which slot contains the active point-to-point NEI (IP Address) + - Indicates the multicast NEI selected.

Both NEIs must be registered concurrently; there is no command to register a multicast NEI by itself. Define and select the multicast NEI before registering the point-to-point NEI. The GMID field in Figure 4-1 is only applicable to the multicast NEIs.

The DART 200 can have multiple Multicast NEIs defined, but can only have one active at a time. The multicast designation for a particular slot in the NEI table can be deactivated by an AT\S-n command, (where n is the slot number), and a different one activated by an AT\S+n command.

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Some software stacks, used when the DART 200 operates in Serial Line Internet Protocol (SLIP) mode, only receive broadcast messages (including multicast) on a specific IP destination address, specifically the point-to-point NEI. To provide for this limitation, the DART 200 permits specifying whether or not the received destination IP Address (multicast address) is replaced with the active point-to-point NEI before the received packet is passed across the SLIP interface to the software stack.

This feature is implemented by using the AT*G command. AT*G1 (default) causes the received destination address to be replaced as described above. AT*G0 passes the received packet across the SLIP interface to the TCP stack unmodified, with the destination address being that of the Multicast NEI.

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5 DART Supported Protocols

UDP

User Datagram Protocol (UDP) is the most basic transmission protocol provided by the Data Access Radio Transceiver (DART) 200. It is a thin protocol, adding only a port specification to the underlying Internet Protocol (IP). It has the same features as IP, that is a best effort, connectionless delivery service with the chief benefit being minimum overhead.

UDP is not considered reliable because packet delivery is not guaranteed. Packets can be lost, duplicated, delayed, or delivered out of sequence. These conditions are not detected, and the sender or receiver is not informed.

UDP is connectionless because sender and receiver are never logically connected. If the intended receiver is not active the message is lost. It is a best effort delivery, because the IP software makes an earnest attempt to deliver the packets, failing only if system resources are overloaded or the underlying networks fail.

Application programs using UDP must accept full responsibility for handling the problems of reliability, including message loss, duplication, delay, out-of-order delivery, and loss of connectivity.

These problems are often treated casually be programmers. Testing done when using highly reliable, low delay local networks may not expose potential failures. This explains why many applications that use UDP work well in a local environment but often fail in dramatic ways on a more global network.

Despite these warnings, UDP is still the most efficient and widely used protocol. Take care in analyzing the application being implemented, the network being used, and the Mobile Application Subsystem (MAS) device involved to determine if an application implementation using UDP is feasible.

• How likely is it that the network being used can cause these

problems?

Small, non-Internet networks are not likely to cause problems.

• How much compute power and programming capability does the

MAS device have?

Lack of available memory or programming capability can preclude adding the needed reliability features into the application.

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While UDP offers the possibility of using fewer data packets and less total bytes to implement an application than TCP, adding the features already described can consume some of these savings, and requires a major programming effort.

The DART 200 provides basic UDP, available since the DART was first commercially available, and the UDP server, which become available with firmware version 3.0.4 for the DART in April, 1996. These are described separately in the following subsections to delineate the setup options and functions available with each.

Basic UDP characteristics

Basic UDP was originally offered on the DART 100 and early versions of the DART 200. It provides a simple UDP communications capability characterized by no server (auto answer) capability, and the need for both sides of the communications session to use a common port number. Without server capability the DART 200 issues a UDP dial (ATDP) command to get into an online state so that it can receive incoming datagrams.

NOTE: The DART implementation of basic UDP requires that both the host and MAS dial commands use the same port number.

Basic UDP communication

Before initiating UDP communication register the DART 200 on the Cellular Digital Packet Data (CDPD) system. Refer to Channel acquisition, p. 2-10, and Registration, p. 2-15, for instructions on registering the DART 200.

To initiate UDP communication:

1. Basic UDP has no auto answer capability, so the modem must be in

online mode before communications can be started. Use the ATD command with the P (for UDP) modifier followed by the IP Address and port number of the destination system (host or another MCDART) to put the DART 200 into online mode. If the DART will be used by a remote device that cannot issue a UDP dial command, then basic UDP is not a viable option; the UDP server option must be used.

2. If no port is specified the default port number (23) is used. Since the

DART listens by default if another DART is the target. If a port number is required, specify it now. Unless the application operates on a closed system, port numbers should be in the range between 1025 to 4999 to comply with industry standards.

Alternatively, the dial could reference an IP Address/port stored in the DART 200 dial list by the ATDPSn command: where n is the number of the desired IP Address in the dial list. Refer to Modem dial directory, p. 8-24, or the &Z command in Appendix F, DART

AT Command Set, for more information.

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Even though a successful ATDP command receives a CONNECT response a connection was not established. The ATDP merely passes

NOTE: Even though a successful ATDP command receives a CONNECT response a connection was not established.

the IP Address and port number of the destination system to the DART 200, where they are stored for use in constructing UDP headers for the data packets that follow. If the communication session is being set up between two DARTs, both have to execute a UDP dial command to go into online mode so that communications can begin.

If data transmission is initiated by the MAS:

1. The MAS writes application data blocks to the DART 200.

2. Data blocks are assembled until a data forwarding condition, as

described in Data forwarding, p. 8-8, occurs.

3. The DART 200 attaches the UDP header and checksum and sends

the packet to the network.

4. The datagram (packet) is directed by the network routers to the

appropriate port on the designated host. If the host or host port is inactive the data is lost and the local application is not informed.

Good UDP application design includes packet sequence checking, and acknowledgments to ensure that both the sender and receiver can determine if all application data arrived successfully.

NOTE: A good error-checking and acknowledgment scheme is essential to successful UDP operation.

If the MAS is on the receiving end:

1. When expecting a message following the initial CONNECT message

or in response to an output message, the MAS reads continuously until all expected data is received.

2. When the data block is received it should be checked against

preceding blocks for sequence errors before proceeding.

3. The DART 200 passes the data portion of the incoming datagram on

to the MAS after removing the source IP Address and port number from the header for use as the destination address in the response (if required). This address data is available to the MAS through S-Register 53 with an ATS53? command; it cannot be viewed with an AT&V.

The handling of network connectivity issues (such as loss of carrier), as well as data delivery and sequencing, is the responsibility of the MAS. Refer to Modes of operation, p. 8-3, for guidelines on handling network errors.

Session termination may or may not be necessary. If the MAS originates sessions, it must terminate the first session before starting a second. Terminate sessions by the escape function followed by a hang-up command (H), as described in Appendix F, DART AT Command Set. If the MAS only receives calls (performs a server function), it can remain in online mode waiting for a datagram (service request) from another client.

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Because UDP is a connectionless protocol, a single M-ES can communicate with multiple M-ESs at the same time as long as timing considerations are closely followed.

When a DART 200 receives a datagram from another M-ES:

1. The DART 200 removes the source address information (IP Address

and port number) and saves it to use as the destination address for its response message.

2. After the DART 200 responds to client #1, it is free to receive and

respond to requests from client #2, #3, and so on. The requests and responses from clients can be interspersed, as long as no request comes in from a client before a response is given to the previous client. If that occurred, the response intended for #1 would go to #2, followed by the normal response to #2.

Unless the timing of requests can be scheduled or controlled to prevent this from happening, avoid this type of operation with basic UDP. The UDP server is designed to handle this, as described in UDP server, p. 5-5.

NOTE: The DART default is basic UDP active. It is strongly recommended that this feature be disabled so that the UDP server function will be active.

The DART 200 with UDP server capability uses a bit in Status (S)-Register 82 to enable and disable basic UDP operation; basic UDP operation is enabled. If you do not have an older DART compatibility requirement, it is strongly recommended that basic UDP not be used. Refer to the bullet point on backward compatibility on p. 5-7, for information on enabling and disabling the basic UDP mode of operation.

Basic UDP setup options

The following items must be set so the DART 200 can operate on the CDPD network:

• IP Address (^A)

• Side Preference (\N in the modem profile)

• Channel restrictions ( \J in the modem profile)

Refer to Basic modem personalization, p. 2-6, for a review of using the AT commands, ^A, \N, and \J.

In addition, the following items are required for basic UDP operation:

• Automatic registration - as described in Automatic registration,

p. 8-6

• PAD mode - \O0 in the profile. Refer to \O command in Appendix F,

DART AT Command Set for details on using this command.

• S-Register 82 set to 2 (default). Refer to the bullet point on backward

compatibility, p. 5-7, for details on setting this S-Register

Many of the following profile parameters may apply and need to be evaluated. Some need to be set to provide the proper application operating environment, others can be allowed to default.

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To set up the options, first, review Chapter 8, Application Programming, and the command descriptions in Appendix F, DART AT Command Set before setting the following parameters, then proceed to step 1.

• Command mode echo (En)

• Data set ready (DSR) operation (&Sn)

• Verbose Mode (Vn)

• Data Forwarding operation (\Fn)

• Quiet mode (Qn)

• Manual transmit control (\Mn)

• Online mode echo (Fn)

• Flow control (\Qn)

• Extended result codes (Xn)

• Automatic transmit control (\Tn)

• Data carrier detect (DCD) operation (&Cn)

• Reception of IP broadcasts (*Bn)

• Data terminal ready (DTR) operation (&Dn)

• Listening Port (*Ln)

• Escape code recognition (&En)

1. Set the key parameter, PAD operating mode (\On), to \O0 for UDP

operation. The default value is \O1, so it must be changed.

NOTE: At present no carrier is offering a broadcast capability.

NOTE: UDP is also the only protocol that can receive multicast messages.

2. UDP is the only CDPD protocol that can receive broadcast messages.

Use the AT*Bn command to allow (B1) or to suppress (B0) reception of broadcast traffic.

3. Check with your carrier to determine if multicast is available in your

area before proceeding to step 4.

4. Direct multicast messages to the modem’s listening port (refer to *L

command in Appendix F, DART AT Command Set). Multicast messages can appear at any time; possibly interspersed with the application data. The end-user’s application must handle the multicast messages interspersed with the application data. For applications with the modem set up to use multicast, be aware that it cannot be suppressed by AT commands.

UDP server characteristics

The DART UDP server is a backward compatible extension to the DART 200 basic UDP implementation with the following additional features:

• Auto-answer capability to permit Remote Terminal Units (RTUs)

with limited capability to use UDP. The RTU is not required to issue a UDP dial (ATDP) command in order to receive messages when the UDP server is active

• Friends Only mode to restrict communications to a specific list

(maximum of 10) of source addresses (IP Address only). This helps prevent unauthorized access to the MAS application

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• Receive locking capability to allow the DART 200 to function as a

UDP server by holding off incoming messages until the preceding message is answered

• Eliminates the need for the M-ES and Host modems to use a

common port number. The server uses the source address contained in the incoming packet as the destination address for outgoing packet

• Backward compatibility with the basic UDP function in earlier

DART modems by an S-Register setting. When there are DART modems involved in the UDP application that use non-server software, activate this feature

These added features make the DART UDP server compatible with industry standard client-server models where the client originates communications and the server waits for incoming communications requests.

UDP server setup options

In addition to the new options discussed here, the same setup options used with basic UDP, as described on p. 5-4, also must be considered before proceeding to step 1.

NOTE: When the listening port is changed it is not active until the server is stopped and restarted, or the modem is reset with an AT-R or a power cycle.

1. Set the defining setup parameter for the UDP server function ( *An -

select server type) to 2 with an AT*A2 command. Selecting this option enables the UDP server function. The default value for this parameter is *A0 (no server active). This is appropriate if the MAS application always operates in client mode; always originates the connection request with an ATDP command.

2. With the UDP server option enabled, choose the method used to

answer incoming calls. The preferred method is to set S-Register 0 = 1 with an ATS0=1 command, which puts the modem into permanent auto answer mode. The alternative is for the MAS to use the answer command, ATA. This command could be used in response to a RING message, or in anticipation of an incoming call. However, in the latter case, since the command is only active for 20 seconds it has to be used in a programming loop to receive a call.

3. (Optional) Select the port to listen for incoming messages on. For

basic UDP the listening port is fixed at 2100. However, with the UDP server the listening port can be set using the *L command. The command format is AT*Ln where n is the desired listening port; a decimal number in the range of 1025 to 4999 for compliance with industry standards.

4. If the listening port is changed, save it with an AT&W. The default

value for the listening port is still 2100 for backward compatibility with basic UDP.

The remaining setup options for the UDP server are controlled by the contents of S-Register 82, including:

• Friends Only mode

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• Receive locking

• Backwards compatibility

The details of these options follow.

• Friends Only Mode - Restricts communication with the modem (for

security reasons) to a predefined group of addresses (friends) This feature is controlled by S-Register 82 which enables and

disables the comparison of datagram source addresses against a list stored in the DART 200’s destination dial directory. Refer to the

AT&Z command in Modem dial directory, p. 8-24, or Appendix F, DART AT Command Set for details. Only the IP Address portion of

the addresses in the dial directory is used with this feature. Bit 0 of S-Register 82 controls this mode. The default is to accept all incoming datagrams (bit 0 = 0).

This bit is significant only when the UDP connection is established passively (server mode). When the connection is established actively (by an ATDP command), incoming datagrams are accepted from the destination address specified in the dial command regardless of the address being in the friends list; this is consistent with basic UDP operation.

In both of the above cases, the source address (IP Address and port number) of the last accepted datagram is saved in a temporary variable for use as the current destination address for all datagrams being sent by the MAS during the current session. This source address information is also saved in S-Register 53 where it can be obtained with an ATS53? command. However, if the application design allows the M-ES to receive messages from multiple clients, outbound datagrams can only be sent to the last source of input data. If this is a potential problem due to timing considerations, refer to the next bullet point on receive locking.

• Receive Locking - A UDP server feature that allows time for the

MAS to respond to a datagram without concern that another datagram from a different source will overlay the current destination address

This feature is controlled by bit 2 of S-Register 82. The default is receive locking disabled (bit 2 = 0). The lock time out period is specified in S-Register 83 in tenths of seconds (default is 3 seconds). If receive locking is enabled, all datagrams arriving after the first one, regardless of their source address, are held in a First-In-FirstOut (FIFO) queue until a data transmission occurs, or the time out period expires, releasing the first datagram in the queue.

• Backward Compatibility - Permits the UDP server to operate in a

mode compatible with the basic UDP provided in earlier versions of the software (prior to version 2.0)

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This feature is controlled by bit 1 of S-Register 82. The default is backward compatibility enabled (bit 1 = 1). When this bit is on the UDP server does not generate a random port number as the source

NOTE: This bit should be set to 0 if there are no DARTs using basic UDP participating in the network.

NOTE: The UDP server is compliant with industry standard client-server models where client systems originate calls and server systems answer calls. Another aspect of these standards is the distinction between active (client) and passive (server) operation.

port when the MAS issues an ATDP, but instead uses the port number specified in the destination address of the dial command. In backward compatibility client mode, the destination port cannot be the same as the modem’s listening port if the UDP server is active.

• UDP server communication - UDP communications with the UDP

server active are similar to those for basic UDP, with the exception of the call establishment operation discussed in Basic UDP communication, p. 5-2. A discussion of call establishment operation with the UDP server active follows.

In active operation (client mode):

1. The MAS (or DTE) issues an ATDP command using the dial

string (ATDPn.n.n.n/x) or the dial list entry (ATDPSn) form to put the M-ES into online mode. If no destination port is specified the port number defaults to the standard telnet port (23); this should be avoided.

2. Unless the application operates on a closed system, use port

numbers in the range of 1025 to 4999 to comply with industry standards. The modem’s protocol stack generates a random number for use as the source port for active mode sessions. However, if the backward compatibility option is active the source port number is forced to be the same as the destination port address specified in the dial string.

As is the case with basic UDP, the CONNECT message received when going into online mode does not imply that a logical connection was established as it does with TCP. Instead, it indicates to the MAS that the modem is in online mode, ready to communicate, and that the destination address is saved for use in constructing packet headers for data that follows.

3. In addition to putting the modem into online mode, the ATDP

generates a random port number for use in the packet source address, which is also used as the active session listening port.

4. If the modem functions only as a client (*A0), the listening port

defined by the *L command is not active. The modem receives datagrams on the active session listening port instead, and only from the destination address (IP Address and port) specified in the dial command.

If the modem functions in a dual role, both as client and server (*A2), there are some additional items to be aware of, including:

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• The modem’s server listening port is disabled for the

duration of any active client session. Incoming datagrams are received on the active session listening port and only from the destination address specified on the dial command until an escape is performed and an ATH is issued; reactivating the server’s normal listening port

• If operating in backward compatibility mode, the destination

port number on the ATDP command must be different from the modem’s server listening port

5. Following receipt of the connect message, application data

written to the DART 200 through the RS-232 port using device specific commands.

6. This data is assembled until a data forwarding condition, as

described on p. 8-8, occurs.

7. The DART 200 then attaches the UDP header and sends the

datagram onto the network.

8. The datagram is directed by the network routers to the

appropriate port on the designated server. If the server is not active when the datagram arrives it is lost, and the client is not informed.

NOTE: How the UDP behaves is dependent on the auto answer mode in use.

In passive operation (server mode):

1. The UDP server listens on the configured port (2100 or *L

specified) for an incoming datagram, then determines if the datagram is to be passed to the MAS and the M-ES put into online mode.

2. With auto answer disabled when a datagram is received by the

UDP server, it first validates the source address (if the Friends Only option is specified), and if it is acceptable issues a RING result code. Refer for Auto Answer setup, p. 8-11, for more details.

3. If an ATA command is not currently active, or is not issued

within 60 seconds, the arriving datagram is discarded and the source address of the arriving datagram is not saved. No indication of this event is presented to the MAS. If the ATA command is, or becomes, active within the time-out period:

• A CONNECT result code is issued

• The modem enters online mode

• The source address is saved

• The datagram is passed to the MAS

4. With auto answer enabled, as described in Auto Answer setup,

p. 4-11, when a UDP datagram is received by the UDP server, the modem first validates the source address (if the friends only option was specified).

5. If the source address is acceptable then a CONNECT result code

is issued.

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• The modem enters the online mode

• The source address is saved

• The datagram is passed to the MAS

In the answering modes already discussed:

1. The modem accepts incoming UDP datagrams.

2. The modem strips off the UDP header, and passes the packets

on to the attached device for processing.

3. Responses are assembled and transmitted as described in steps 1

and 2 for UDP clients.

4. The modem continues in this mode, accepting and transmitting

data until the MAS explicitly moves the modem to command mode by issuing an escape sequence (+++), or by dropping DTR with a non-zero &D option specified.

5. Now, the MAS can return to online mode with the ATO

command, or drop out of the CONNECTED state with the ATH command. Issuing a hang up command (ATHn) causes the current source (S-Register 53) and destination address to be reset, and the UDP server to automatically listen for the next datagram. At this point, both passive and active connection requests will be honored.

NOTE: The DART 200 has approximately 6K of buffer space available for storing queued datagrams.

A MAS functioning as a server receives calls from any client device. However, it can only save one source address, the one that was extracted from the last datagram received, for sending any required response. For this reason, if multiple clients are expected server modems must use receive locking to delay accepting subsequent datagrams until a response is sent to the source of the prior datagram. Datagrams subsequent to the first are placed in a FIFO queue for later processing.

In both client or server modes, the modem extracts the source address (IP Address and port number) from the first packet received and stores it in S-Register 53. This information can be retrieved by the end-user application, if needed, with an ATS53?, for example:

ats54?

198.225.189.21,4000

This address data cannot be viewed with the AT&V command. The data remains in S-Register 53 until the session is ended by an ATH command (client mode), or a datagram is received from a different source (server mode).

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Sample UDP server setups

These settings give a general sense of the AT commands required to set up a DART 200 for a UDP application. All relevant AT commands are listed, including the defaults. All devices function differently, so the setups that follow are general. These setups show specific items to examine, but it is good practice to examine all of the setup values.

Two UDP setup examples are given:

• Remote UDP setup - A remote telemetry application and a central

client application, that shows the setup for a server modem at an RTU being polled by a host computer

• Host UDP setup - shows the setup for a client modem at the host

computer that does the polling. This modem at the host arrangement is suitable for bench-testing and limited use pilot implementations. Production systems normally are direct connected through a leased line or frame relay to a router at the customer’s host system (F-ES)

Remote UDP setup

The remote modem is set up as a server at the remote telemetry unit where it responds to polls from a host computer. The sample RTU does not use flow control and the data being sent is binary, not character, data. This requires the UDP server to be set up with auto answer to respond to polling, no flow control, and timed data forwarding because of the binary data.

In Table 5-1, line items marked with an R (required) or an O (optional) were changed from the default (D). After the changes are made save them with an AT&W.

Table 5-1. Remote UDP setup

AT Command Req Opt Def Description

AT^Annn.nnn.nnn.nnn AT\N[1,2] AT\J0

AT\R4 ATS13=0

AT\O0 AT*A2 AT*L2100 ATS0=1 ATS82=0

R R

D Use default - No channel access

R R

D Use default - Listen on port 2100

O R

Input IP Address (if not already done) Side Preference (get from carrier)

restrictions Auto Registration at Power On With AT\R4 sets Continuous Automatic Registration PAD mode required for UDP. Set UDP Server mode

Activate auto answer for server Turn off backward compatibility. Consider friends only mode if unauthorized access is a concern.

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Table 5-1. Remote UDP setup (cont.)

AT Command Req Opt Def Description

ATE0 ATV0 ATQ0

O O

D Use default - Result codes are sent to

No command mode character echo Use terse result codes

the RTU

ATF1

D Use default - Do not echo transmitted

data to the RTU

ATX1 AT&C1

D Use default - Extended result codes D Use default - DCD follows state of

the connection

AT&D0

D Use default - You may want to

consider using DTR to escape if RTU supports it

AT&E2 AT&S0 AT\F3

D Use default - DSR is always active D Use default - Applies only if \M1

Filter escape sequence from output

specified

AT\M0

D Use default - Do not recognize data

forwarding characters

AT\Q0 AT\T1

D Timed data forwarding - Always use

Most RTUs do not use flow control

with binary data

AT*B0

D Use default - Many CDPD Carriers

have not implemented Broadcast.

AT*C1 AT*G1 AT*K0 AT*R0 AT*T0

D Use default - Does not apply to UDP D Use default - Does not apply to UDP D Use default - Does not apply to UDP D Use default - Does not apply to UDP D Use default - Does not apply to UDP

Host UDP setup

The host (client) modem is set up to support polling of remote devices by the host computer. The specific host uses flow control and the data being sent is binary, not character, data. The polling function does not require the UDP server, but requires flow control, and timed data forwarding because of the binary data.

Use this setup only for bench testing or a limited use trial. A production application uses a leased line, frame relay, or Internet connection between the host and the MDIS instead of a modem. In the latter scenario, the production host application needs to interface with a software stack (replacing the modem stack to operate with the CDPD network).

In Table 5-2, only the line items marked with an R or an O are changed from the default (D). After making changes, save them with an AT&W.

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AT^Annn.nnn.nnn.nnn

Table 5-2. Host UDP setup

AT Command Req Opt Def Description

Input IP Address (if not already done) Side Preference - (get from carrier)

AT\N[1,2] AT\J0

R R

D Use default - No channel access

restrictions

AT\R4 ATS13=0

R R

Auto Registration at Power On With AT\R4 sets Continuous Automatic Registration

AT\O0 AT*A0

D Use default - No server function

PAD mode required for UDP.

required

AT*L2100 ATS82=0 ATE0 ATV0 ATQ0

D Use default - Listen on port 2100

R O O

Turn off backward compatibility. No command mode character echo Use terse result codes

D Use default - Result codes are sent to

the host

ATF1

D Use default - Do not echo transmitted

data to the host

ATX1 AT&C1

D Use default - Extended result codes D Use default - DCD follows state of

the connection

AT&D0

D Use default - You may want to

consider using DTR to escape

AT&E2 AT&S0 AT\F3

D Use default - DSR is always active D Use default - Applies only if \M1

Filter escape sequence from output

specified

AT\M0

D Use default - Do not recognize data

forwarding characters

AT\Q2

D Use default - Most PC’s use flow

control

AT\T1

D Timed data forwarding - Always use

with binary data

AT*B0

D Use default - Many CDPD Carriers

have not implemented Broadcast.

AT*C1 AT*G1 AT*K0 AT*R0 AT*T0

D Use default - Does not apply to UDP D Use default - Does not apply to UDP D Use default - Does not apply to UDP D Use default - Does not apply to UDP D Use default - Does not apply to UDP

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TCP

Transmission Control Protocol (TCP) is an advanced transmission protocol that adds substantial functionality to the underlying Internet Protocol it is built on. Because of this structure it is often referred to as TCP/IP. The advantage of TCP is reliability of data transmission; achieved by using positive acknowledgments with retransmission if required. The main disadvantage is the overhead needed to provide this reliability under any and all conditions.

Unlike UDP, TCP offers both reliable and connected data transmission service. Lost, delayed, duplicated, or out of sequence packets are detected and automatically corrected. A logical point-to-point connection is established and maintained throughout the communications session. TCP is ideally suited for applications where speed of development is critical, or for applications where the MAS is low on compute power, available memory, or both. It requires very little other than session establishment, sending data over the serial port, and session termination to get a basic application operational.

The price for this reliability is the number of extra data packets used and the time required to process them. Both need to be considered when selecting an application protocol.

DART TCP capabilities

The DART software stack offers industry standard client-server capability where the client originates communications and the server waits for incoming requests. In server mode it includes auto answer capability and an optional Friends Only mode. Friends Only mode restricts the devices the server can receive calls from to help prevent unauthorized access to applications or devices.

Friends Only mode operation

Friends Only mode permits communication with the modem to be restricted (for security reasons) to a predefined group of addresses (friends). Friends Only mode is controlled by S-Register 82, that enables and disables the comparison of packet source addresses against a list stored in the DART 200’s destination dial directory. Refer to the Modem

dial directory, p. 8-24 AT&Z command in Appendix F, DART AT Command Set, for details. Only the IP Address portion of the addresses

in the dial directory is used with this feature. Bit 0 of S-Register 82 controls this mode. The default is to accept all incoming datagrams (bit 0 = 0).

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This bit is significant only when the TCP connection is established passively (server mode). When the connection is established actively (by an ATDT command), incoming packets are accepted from the destination address specified in the dial command regardless of whether or not it is contained in the friends list.

In both modes of operations, the source address (IP Address and port number) of the last accepted packet is saved in a temporary variable for use as the current destination address for all packets being sent by the MAS during the current session. This source address information is also saved in S-Register 53 where it can be obtained with an ATS53? command.

TCP communication

To participate in a TCP session the DART 200 must be registered on the CDPD system. Refer to Channel acquisition, p. 2-10, and Registration, p. 2-15 for details on registering the DART 200 on the CDPD network.

A TCP session can be started by the central site system (host or F-ES) or remote system (MAS); it is application dependent. If the MAS is the client it starts a session with the ATD command and the T (for TCP) modifier followed by the host IP Address and port number (Ex. ATDT198.225.176.43/2100). If no port is specified the port number defaults to the standard telnet port (23); this should be avoided.

Unless the application is being run on a closed system, use port numbers between 1025 and 4999 for compliance with industry standards. Alternatively, the dial could reference an IP Address/port stored in the DART 200 dial list by the ATDTSn command where n is the position number of the desired IP Address in the dial list. Refer to the &Z command in Modem dial directory, p. 8-24, Appendix F, DART AT Command Set, for more details.

When a connection with the server is established:

1. The modem enters online mode and presents a CONNECT response

to the MAS. It is customary (but not required) for the client to do the first data transmission.

2. The MAS begins data transfer by writing application data to the

DART 200 through the RS-232 port using device specific commands.

3. This data is assembled until a data forwarding condition occurs, as

described in Data forwarding, p. 8-8.

4. The DART 200 attaches the TCP header and sends the packet onto

the network.

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5. The data packet is directed by the network routers to the appropriate

port on the designated server. If the server or the data path becomes inactive between the time the connection is established and the time data transmission starts, the MAS is informed by an error message being returned.

If the central site is the client establishing the TCP session, the modem at the remote site must be set up in TCP sever mode. The MAS can wait for

NOTE: Time-outs are not a consideration if auto answer is enabled.

a RING message and respond with an ATA command, or its modem can have auto answer active. Refer to Auto Answer setup, p. 8-11, for details on activating this option.

Unlike UDP, with TCP a session is established by a three-way handshake between the client and the server, not by the initial datagram. The client IP Address is part of the incoming session establishment packet. When the TCP handshake is received by the TCP server, the modem first validates the source address (if the Friends Only option was specified).

If the source address is acceptable or if Friends Only is not active then a RING result code is issued.

• If auto answer is active the CONNECT message is issued. If not,

then an ATA must be issued by the MAS within 60 seconds or the tentative connection will be dropped.

NOTE: The address remains in S-Register 53 until the session is ended by an ATHn command.

• The modem extracts the source address (IP Address and port

number) from the handshake packet for use in constructing the response data packets and also stores it in S-Register 53. This data can be retrieved by the end-user application, if needed, with an ATS53? The address data cannot be viewed with the AT&V command:

ats53?

198.225.189.21.4000

• The modem enters online mode.

If the source address is not acceptable, the connection is refused. In either client or server mode:

1. When the connection is established a CONNECT message is

received.

2. The MAS continues to read from (server) or write to (client) the

serial port to exchanges data packets with its session partner.

3. If data is being sent, it accumulates until a data forwarding condition,

as described in Data forwarding, p. 8-8 occurs:

• The DART 200 then attaches the TCP header and sends the

packet onto the network

• The packet is directed by the network routers to the appropriate

port on the designated server

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4. Once the data block is received it is ready for processing. Any

necessary error-checking, resequencing, and so on, is handled by the TCP software and is not the responsibility of the MAS. The handling of network connectivity issues (such as loss of carrier), as opposed to data delivery and sequencing (provided by TCP), is the responsibility of the MAS. Refer to Error recovery, p. 8-4, for guidelines on error handling.

5. Once the first data block has been received, the server system (MAS

or central site depending on application design) could reply to the client system with data of its own, or it could wait for additional data from the client. The variations at this point are numerous and entirely dependent on application design.

6. When data transfer is complete the session terminates. As with the

initial communication step, either end could terminate; it is another application design decision, but usually, the client terminates.

7. If the MAS is the server, it receives a NO CARRIER message and

returns to command mode when the client terminates the session. If the MAS is the client, it performs an escape function to return to command mode followed by a hang-up command (H). Refer to Appendix F, DART AT Command Set, for a description of H.

Setup options

The following items must be set to enable the DART 200 to operate on the CDPD network:

• IP Address (^A)

• Side Preference - \N in the modem profile

• Channel restrictions - \J in the modem profile

Refer to Basic modem personalization, p. 2-6, for a review of the details on the AT commands ^A, \N, and \J.

In addition the following items are required for basic TCP operation:

• Automatic registration. Refer to p. 8-6 for details

• PAD mode - \O0 in the profile. Refer to \O command in Appendix F,

DART AT Command Set

If application design dictates that the MAS accepts connection requests, activate the TCP server by setting the *A (select server type) AT command to 1 with an AT*A1. Selecting this option enables the TCP server function. The default value for this parameter is *A0 (no server active). The default option is appropriate if the MAS application always operates in client mode; always originates the connection request with an ATDT command.

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Many of the following profile parameters apply and need to be evaluated before proceeding to step 1. Some need to be set to provide the proper application operating environment, and others can be allowed to default. Review application programming in Chapter 8, Application

Programming, and the command descriptions in Appendix F, DART AT Command Set.

• Command mode echo (En)

• Data set ready (DSR) operation (&Sn)

• Verbose mode (Vn)

• Data forwarding operation (\Fn)

• Quiet mode (Qn)

• Manual transmit control (\Mn)

• Online mode echo (Fn)

• Flow control (\Qn)

• Extended result codes (Xn)

• Automatic transmit control (\Tn)

• Data carrier detect (DCD) operation (&Cn)

• TCP PAD Keep-alives (*Kn)

• Data terminal ready (DTR) operation (&Dn)

• Set Listen Port (*Ln)

• Escape code recognition (&En)

1. Set the key parameter, PAD Operating mode (\On), to \O0 for TCP

operation.

2. If the modem is to be set up as a server to answer incoming calls

(connection requests), select the method to be used. There are two options available: setting S-Register 0 = 1 with an ATS0=1 command is the preferred method. This option puts the modem into permanent auto answer mode. The alternative is for the MAS to wait for the RING message, indicating an incoming connection request, and then use the answer command, ATA, to establish the connection.

3. Select the port for the DART 200 to listen on for incoming messages

with *L command by using an AT*Ln, where n is the desired listening port. Unless you are operating on a closed network, use a decimal number in the range of 1025 to 4999 for compliance with industry standards. The default value for the listening port is 2100 for backward compatibility with earlier versions of the modem.

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4. In any TCP application where the remote system only operates in

server mode, consider the use of the TCP keep-alive option (*K). It is possible for the central client system to fail after establishing a session with a remote server. If the client fails its end of the TCP session closes, but the server end remains open.

Attempts to re-establish the connection with the server after the client recovers get a BUSY response because the prior session was not properly closed. The receive keep-alive option (*K2) enables a remote server to close its side of a session if data or a keep-alive character is not received within an end-user specified timeout period. The time out period is contained in S-Register 86 (default 120 minutes). A reasonable timeout value is on the order of 3 to 5 minutes.

The remaining parameters are application dependent and are covered in detail in Chapter 8, Application Programming.

Sample TCP setups

These settings give a general sense of the AT commands required to set up a DART 200 for a TCP application. All relevant AT commands are listed, even the defaults. All devices function differently, therefore, the setups listed in this section of the manual are general. These setups show specific items to examine, but it is a good idea to examine all of the setup values.

Two TCP setup examples are shown below: a remote telemetry application and a central client application. Remote TCP setup, p. 5-19 shows the setup for a server modem at a remote telemetry unit (an RTU) being polled by a host computer.

Host TCP setup, p. 5-21, shows the setup for a client modem at the host computer that does the polling. This modem at the host arrangement is suitable for bench testing and limited use pilot implementations. Production systems normally are direct connected through a leased line or frame relay to a router at the customer’s host system (F-ES).

Remote TCP setup

The remote modem is set up as a server at the remote telemetry unit where it responds to polls from a host computer. The specific RTU does not use flow control and the data being sent is binary, not character, data. This requires the TCP server with auto answer to respond to polling, no flow control, and timed data forwarding because of the binary data.

In Table 5-3, the line items marked with an R (required) or an O (optional) are changed from the default (D).

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Table 5-3. Remote TCP setup

AT Command Req Opt Def Description

AT^Annn.nnn.nnn.nn n

AT\N[1,2] AT\J0

R R

D Use default - No channel access

Input IP Address (if not already done) Side Preference (get from carrier)

restrictions

AT\R4 ATS13=0

R R

Auto Registration at Power On With AT\R4 sets Continuous Automatic Registration

AT\O0 AT*A1 ATS0 =1 AT*L2100 ATE0 ATV0 ATQ0

R R

D Use default - Listen on port 2100

O O

D Use default - Result codes are sent to

PAD mode is required for TCP Sets TCP Server mode Set modem to Auto Answer

No command mode character echo Use terse result codes

the RTU

ATF1

D Use default - Do not echo

transmitted data to the RTU

ATX1 AT&C1

D Use default - Extended result codes D Use default - DCD follows state of

the connection

AT&D0

D Use default - You may want to

consider using DTR to escape if RTU supports it

AT&E2 AT&S0 AT\F3

D Use default - DSR is always active D Use default - Applies only if \M1

Filter escape sequence from output

specified

AT\M0

D Use default - Do not recognize data

forwarding characters

AT\Q0 AT\T1

D Use default - Timed data forwarding

Most RTUs do not use flow control

should always be used with binary data

AT*B0 AT*C1 AT*G1 AT*K2 ATS86 = 3 AT*R0 AT*T0

D Use default - Does not apply to TCP D Use default - Does not apply to TCP D Use default - Does not apply to TCP

O O

Set TCP receive keep-alives

Use 3 minute keep-alive timeout D Use default - Does not apply to TCP D Use default - Does not apply to TCP

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Host TCP setup

The host (client) modem is set up to support polling of remote devices by the host computer. The host uses flow control and the data being sent is binary, not character data. The polling function does not require the TCP server, but requires flow control, and timed data forwarding because of the binary data.

Use this setup only for bench testing or a limited use trial. A production application uses a leased line, frame relay, or Internet connection between the host and the MDIS instead of a modem. In the latter scenario, the production host application needs to include a software stack (replacing the modem stack) to operate with the CDPD network.

In Table 5-4, only the line items marked with an R (required) or an O (optional) are changed from the default (D).

Table 5-4. Host TCP setup

AT Command Req Opt Def Description

AT^Annn.nnn.nnn. nnn AT\N[1,2]

AT\J0

AT\R4 ATS13=0

AT\O0 AT*A0 AT*L2100 ATE0 ATV0 ATQ0

ATF1

ATX1 AT&C1

AT&D0

AT&E2 AT&S0 AT\F3

AT\M0

AT\Q2

AT\T1

AT*B0 AT*C1 AT*G1

R R

D Use default - No channel access

R R

D Use default - No server required D Use default - Listen on port 2100

O O

D Use default - Result codes are sent to the

D Use default - Do not echo transmitted

D Use default - Extended result codes D Use default - DCD follows state of the

D Use default - You may want to consider

D Use default - DSR is always active D Use default - Applies only if \M1

D Use default - Do not recognize data

D Use default - Most PC’s use flow

D Timed data forwarding - Always use

D Use default - Does not apply to TCP D Use default - Does not apply to TCP D Use default - Does not apply to TCP

Input IP Address (if not already done) Side Preference (get from carrier)

restrictions Auto Registration at Power On With AT\R4 sets Continuous Automatic Registration PAD mode is required for TCP.

No command mode character echo Use terse result codes

host

data to the host

connection

using DTR to escape Filter escape sequence from output

specified

forwarding characters

control

with binary data

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Table 5-4. Host TCP setup (cont.)

AT Command Req Opt Def Description

AT*K0

AT*R0 AT*T0

D Use default - Keep-alives not needed at

central site D Use default - Does not apply to TCP D Use default - Does not apply to TCP

SLIP

Serial Line Interface Protocol (SLIP) is the defacto standard for encapsulating TCP/IP protocol over dedicated and/or switched serial lines. It is a useful and reliable way to allow mixes of hosts and routers to communicate with one another in various combinations.

Most casual end-users do not encounter SLIP in the above form. Instead, they find SLIP being used with TCP/IP stacks (usually referred to simply as stacks) in a variety of PC programs designed to provide support for multiple TCP or UDP applications over networks of various types (X.25, LANs, satellite, and so on) including the Internet. CDPD is another such network.

These stacks frequently include additional functions such as electronic mail, various forms of telnet, ping, Internet browsers, and file downloading using File Transfer Protocol (FTP). In addition, most of these programs provide a multitasking end-user application programming interface (API) to the stack (usually, Winsock), for developing custom communications applications. These programs are also used with PCs attached to the CDPD network.

The DART 200 provides SLIP capability. When operating in SLIP mode, the modem’s internal TCP/IP stack is bypassed (but not its CDPD stack) and, the modem acts as a router passing data between the software package’s stack, and the network, such as the Internet or a private network using Internet Protocol, attached server applications.

Using such a package allows the design of applications that need multiple communications sessions active concurrently. For example, a public safety application where a police car has active sessions simultaneously with the NCIC in Washington, the State Bureau of Motor Vehicles, and the local police system.

Modem setup for SLIP

In SLIP mode, the following profile parameters are not operational and can be ignored. Their function is provided by the PC-based software package.

• Data forwarding operation (\Fn)

• Select Server Mode (*An)

• Manual Transmit Control (\Mn)

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• TCP/IP keep-alives (*Kn)

• TCP PAD operating mode (\On)

• Telnet keep-alives (*Tn)

• Automatic transmit control (\Tn)

The following profile parameters are operational in command or SLIP modes and need to be evaluated to determine their proper settings:

• Command mode echo (En)

• Data set ready (DSR) operation (&Sn)

• Online mode echo (Fn)

• Restrict Channel Selection (\Jn)

• Quiet mode (Qn)

• Side preference (\Nn)

• Verbose mode (Vn)

• Flow control (\Qn)

• Extended result codes (Xn)

• Reception of IP broadcasts (*Bn)

• Data carrier detect (DCD) operation (&Cn)

• SLIP TCP header compression (*Cn)

• Data terminal ready (DTR) operation (&Dn)

• SLIP Multicast address selection (*Gn)

• Escape code recognition (&En)

• Automatic SLIP Restart (*Rn)

SLIP Header Compression (*C) and Flow Control (\Q) are the key parameters. They must match the stack settings for SLIP to operate.

1. Setting SLIP header compression on saves a small amount of time

(recommended) in data transfer. In most commercial software stacks this feature, if offered, is identified as CSLIP. The default setting for this parameter is *C1 (enabled). If this setting and that of the stack do not match SLIP cannot operate successfully. If your stack does not support compression, you must deactivate it on the DART. To do this execute an AT&C0, and save it with an AT&W.

2. Use hardware flow control (\Q2 - default). If this setting and that on

the stack do not match SLIP cannot operate successfully. Software flow control or no flow control are inappropriate.

3. Set Channel Restrictions (\J), and Side Preference (\N)

appropriately, as described in Basic modem personalization, p. 2-6, but these settings are CDPD, not SLIP related.

4. Set the COM port for 8 data bits and NO parity (8N1). Since SLIP

operates in binary mode, a data byte could be any 8-bit configuration, so parity must be disabled to permit proper operation.

5. Set the DART 200 COM port speed to match that of the stack: 19.2

Kbps is recommended. This can be accomplished by an AT&L &W command.

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Automatic SLIP restart specifies that the DART 200 always enters SLIP mode following power on or modem reset. It lets Winsock applications rely on the modem always being in SLIP mode, particularly following a power off/on cycle.

When this feature is active the modem is not in command mode following power on. This can sometimes be inconvenient. Any time that it is necessary to send AT commands to the modem, at initial application startup or when querying modem status an escape function must be performed (refer to &E or &D commands) before the modem responds to AT commands. If using the manual escape function, check that both the terminal emulation program and the modem are set to the same baud or the escape will not work.

1. This capability is activated with an AT*R1 command (deactivate it

with an AT*R0). Bit 6 of S-Register 57 (value of 64) indicates that auto slip mode is active. A modem that acquired a CDPD channel (128), and used the auto registration feature (32) to get registered (1) shows a value of 225 in S-Register 57 with Auto SLIP Mode Startup (64) active.

2. Save the setting with the &W command to become a permanent

setting.

3. To make the command active, power cycle or reset the modem with

the AT-R command.

SLIP IP Address overview

• Internet Address Classes

CDPD Internet addresses are 32-bit fields consisting of a network ID followed by a device ID (netid, devid). For readability, these 32-bit addresses are broken down into four 8-bit fields (called octets or bytes) that are then converted to their decimal equivalents and separated by a period. For example, the address 11000000 00001110 10100111 00010101 (hardly readable) is represented as

192.14.167.21 Internet standards further define five classes of addresses, the first

three (A,B, and C) of which are used for network addresses.

• Class A addresses have a first octet between 1 and 127, and

consist of a one octet network address followed by a three octet device address

• Class B addresses have a first octet between 128 and 191, and

consist of a two octet network address followed by a two octet device address

• Class C addresses have a first octet between 192 and 255, and

consist of a three octet network address followed by a one octet device address. Most CDPD addresses are class B or class C

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(Terminal)

Link

A simplified block diagram of a terminal connection to a CDPD network using the SLIP interface is shown in Figure 5-1.

Figure 5-1 Terminal connection to a CDPD network using SLIP

AirLinkRS-232

#1 #2 #3

MAS

M-ES MC-DART

CDPD Network

#1 - Local Terminal (MAS) IP Address #2 - DART SLIP Interface IP Address #3 - DART (registered NEI) IP Address

The three IP Addresses are:

1. Local Terminal (MAS) IP Address is set using by AT*Mn.n.n.n

This MAS address is not known to the CDPD network, so it is set by convention to the same value as the one used for #3, as described in item 3 on p. 5-25, to improve performance of the DART 200’s routing mechanism and to ensure that FTP protocol works properly.

2. The DART SLIP Interface IP Address is set using the service

provider command AT^Sm.m.m.m The SLIP IP Address is an arbitrary value, usually 1.1.1.2, because it

is only used by the MAS and DART 200 and is not known to the network. In the definitions for commercially available stacks used with SLIP this IP Address is referred to as the router, gateway, or server address. This address must be present in SLIP definitions for your stack or you cannot run SLIP with the DART 200.

There are two issues involving this address to consider:

• Some TCP/IP software stacks do a validity check on all of these

addresses and require them to be of the same class as the NEI

• The SLIP IP Address must be on a different subnetwork than the

NEI. If it is not, the DART cannot route packets (pings included) to the CDPD network

The suggested resolution to these constraints (if 1.1.1.2 does not work) is to set the network (class) portion of the DART SLIP address to be off by one from the NEI’s network address, and to set the device address to all ones, for example:

Class NEI SLIP Address

Class A 111.155.189.21 110.1.1.1 Class B 155.160.147.17 155.161.1.1

Class C 196.37.111.165 196.37.110.1

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3. The DART (registered NEI) IP Address is known to the network and

is obtained from your service provider. This IP Address is set using the following service provider command: AT^An.n.n.n/x, where: x defines which slot (0-9) in the address table to use. If not entered, x defaults to 0.

If there is more than one NEI stored in the modem’s NEI list the desired one is selected by using the following command: AT\Sn, where: n = 0 to 9

The IP Address selected for use as the NEI remains fixed until specifically changed by using the AT\S command.

NOTE:

• All three IP

Addresses cannot be the same

• For FTP, #1 and

#3 (in Figure 5-1) must be the same

• All three can be

different for non-FTP communications, but performance is somewhat better if #1 and #3 are the same

To view the list of IP Addresses as well as the MAS and SLIP IP Addresses use the AT\S? command: the active NEI has an * to its left, for example:

at\s? SLIP = IP ADDRESS 001.001.001.002 MAS = IP ADDRESS 155.174.048.173

NEI 0 = IP ADDRESS 155.174.036.087 *NEI 1 = IP ADDRESS 155.174.048.173 SPNI 00000 LSA 00000

SLIP operation

The SLIP operation process is as follows:

1. SLIP starts with the AT*S command.

2. This command puts the modem into SLIP mode and gives an OK

response.

3. When in SLIP mode the DART 200 passes all IP and higher layer

protocols (TCP, UDP, telnet) to the TCP/IP stack in the MAS for processing, but continues to handle the lower CDPD protocol layers including the data encryption function. Data forwarding defaults to a transparent, symbol-based method where the symbol is the SLIP end-of-packet character.

4. The modem stays in SLIP mode until an escape function is

performed by the end-user application; by either sending the escape sequence, or by dropping DTR.

5. To return to SLIP mode another AT*S must be issued. An example of SLIP setup for Trumpet, a commonly available shareware

Winsock, is shown in Appendix D, SLIP Setup Examples.

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SLIP initial testing

After the IP Addresses are set, the SLIP setup is completed, and the modem has been put into SLIP mode, determine if your setup is correct and that you have network connectivity by pinging the network.

The ping command format can vary slightly depending on the program you are using. However, the following discussion provides basic guidance regardless of the TCP/IP stack used. The general format of the ping command is: PING nnn.nnn.nnn.nnn

The ping sends a fixed length of data (L) with an echo request to IP Address nnn.nnn.nnn.nnn and waits for a time out period (T) for a response. L and T can be quite different from one program to another, as well as from the DART 200 ping values used with the AT*P command. Consider the differences in these values between your program and the DART 200’s AT*P when comparing results.

The DART 200 default ping values are L= 68 bytes, and T=10 seconds, that result in ping times in the range of 600 to 1600 ms. Most SLIP packages use a larger L and a smaller T than the DART 200, because they were originally designed for land lines or Local Area Networks (LANs) where ping times are much faster than with CDPD. Executing a SLIP ping with its own default parameters over CDPD frequently causes time-outs. If this occurs shorten the SLIP ping data length or increase the timeout period to get successful pings.

TIP: It's helpful when testing to have two DARTs to ping between. This gives you control over both ends of the link, and can be done using a single PC. Register the first DART using your PC, then switch the PC to the second DART, bring up SLIP, and ping back to the first modem. A registered modem does not need an attached

PC to respond to a ping provided it is not in SLIP mode.

To validate that you have set up the SLIP session between the DART 200 and the stack correctly:

1. Ping the modem. Make the modem’s SLIP address (1.1.1.2) the

target. If this ping operation is successful it demonstrates that your setup is correct. This test can be done without being registered or without CDPD being active.

2. Ping the DNS or a server at the local carrier. This Server IP Address,

like the DNS, is available from the carrier. If this ping operation is successful, the SLIP system can communicate with the carrier.

If the ping fails and you are using a modem SLIP address other than

1.1.1.2 , you may have a routing problem. Refer to item 2 on p.5-25, for guidance.

3. Ping an IP Address on the other side of the MDIS; usually, this is a

server, or a test terminal near you.

If this is successful, your SLIP system has network connectivity and is now fully operational. If this ping attempt fails for reasons other than time-out, suspect a bad IP Address, an unregistered IP Address, or a router failure at the MDIS.

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Telnet

The telnet capability within TCP/IP is designed to provide support for ASCII terminals to communicate with text-oriented server applications on host systems. As implemented in the DART 200, the telnet support mode provides the capability for the modem to emulate such a terminal; the default is the DEC VT100 but the actual type is negotiated with (dictated by) the server.

A device (usually a PC, but potentially an ASCII terminal) attached to the DART 200 and using telnet mode has its data stream translated to that of the VT100 or whatever other terminal type was negotiated. This usually involves not only translating a few control characters, but also turning off the high order bit of each data character. This translation can make it very awkward to use telnet mode for a typical telemetry application. It is strongly recommended that telnet not be used for other than the intended use; providing access to ASCII terminal application servers.

Setup options

With the exception of the side preference, the DART 200 factory defaults permit a telnet session to be established. However, certain profile parameters need to be checked to ensure they work appropriately with the remote host at minimum cost, as follows:

• Online Mode Echo (ATFn) - Controls the echoing of characters

when in online mode. The default for telnet mode is F1 (host echo) When a telnet session starts, one of the items that the DART 200

negotiates with the host is whether the host or modem provides the echo for characters entered at the modem end of the connection. Most processes connected on the well-known telnet port (23) provide the echo. However, in a CDPD telnet session where charges are based on packet and data flow rather than on connect time, there is a big incentive to minimize the flow of extraneous information; use the F0 option (modem echo) to do this.

The tradeoff is one of cost versus the confirmation that the characters arrived correctly, which is presumed if they echo back correctly from the host. Also, the client has no knowledge of how certain characters, such as a backspace (BS), should be handled locally since the remote process is what determines if a BS is destructive or harmless.

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• Data Forwarding Operation

• Manual Transmit Control (AT\Mn) - Controls the use of the

characters (specified in S-Registers 51 and 52) for data forwarding while in online mode. The default for this parameter is \M0 (disabled). The default for S-Register 51 is <CR>, that takes effect only if manual transmit control is enabled.

• Automatic Transmit Control (AT\Tn) - Controls the use of the

inter-character time-out period (specified in S-Register 50) for data forwarding when in online mode. The default for this parameter is \T1 (enabled)

With the defaults listed above in effect, characters are transmitted to the telnet host process (remote login or gopher) and echoed back from the remote system for display as they are entered. This generates a lot more packets, but ensures an accurate display of the data as seen by the host application.

If your telnet host process operates correctly with, or requires block mode data transfers (a string of characters followed by a <CR>), then set local echo (F0), manual transmit mode enabled

(\M1, and disable inter character data forwarding (\T0). A local

echo is recommended, in this case, so you can view keys as you enter them without pressing the <CR> key.

• Telnet Keep-Alive - Allows the DART 200 to keep a telnet

session alive (not time out) if the terminal user has excessive think time between entries. Without this capability the telnet session could be terminated prematurely by the server

This facility can work in transmit mode, receive mode, or both. It uses a non-intrusive telnet NOP command packet and a keep-alive time-out value (S-Register 86) to implement the function. The keep-alive timer restarts when data is sent or received regardless of the mode selected (transmit, receive, or both).

If the timer expires with the transmit option specified, pending data or the telnet NOP command is forwarded. If the NOP (keep-alive) is sent the telnet server protocol ignores it, but the session is not allowed to time out. This is the normal use of the function.

If the timer expires with the receive option specified, an ATH command is issued to close the connection.

The default for this function is *T0 (not enabled). Refer to the *T command in Appendix F, DART AT Command Set, for details on how to use this command.

• Linefeed after <CR> - S-Register 1 controls whether or not a linefeed

(<LF>) is sent with a carriage return (<CR>), for telnet mode only. The default is 1 (send <LF> with <CR>). When not enabled, a NULL character follows the <CR> as specified by telnet protocol

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• Terminal Emulation Negotiation - S-Register 78 determines the

terminal emulation type to offer first when negotiating with the telnet host system. The current list is:

• 0 = DEC-VT100 (default)

• 1 = DEC-VT52

• 2 = UNKNOWN

Default is for most specific first, such as 0. When the telnet session is established and negotiation is complete, the actual terminal type chosen is determined by using the telnet escape mode status command, or by an appropriate command for the remote server. If UNKNOWN was selected, the backspace and delete keys may not work correctly. If this is the case you have two options:

1. Use the erase character definition on the remote server. UNIX

usually uses the tset, stty, or printen commands to access terminal parameters. Refer to a UNIX manual or ask the serving system administrator.

2. Use the telnet virtual terminal erase character command to send the

erase character.

Telnet escape commands

When in a telnet session, entering a Ctrl ^ means that telnet interprets the next keystroke as a command. The commands include:

e Send Telnet Virtual Terminal erase character command. i Send Telnet IP command (Interrupt Process). l Tell server you are going to local echo mode r Request server to perform remote echo usually responds [YES] if

there

a Send a telnet AYT Are You There (AYT) command; Server

usually responds YES if there

b Request Binary Mode. This is not normal, use with caution o Request to turn Binary Mode off s Print current status of telnet session. (Local parameters) ^ Send the local telnet escape character.

Any other key that follows the ^^ sequence displays a list of allowed commands. S-Register 77 contains the telnet escape character (default is ^^ or decimal 30.

Some of the DART 200 profile parameters (\Mn, \Tn, and so on) can be changed after logging in to the telnet host by using the DART 200’s escape to command mode sequence (+++). However, do not change S-Register values and modem profile parameters that were negotiated with the remote host when in the connected state, since changing their values at this point could impact client/remote host communication. After completing your changes, return to the telnet session with the ATO command.

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New for this version

The telnet binary mode (\Bn) was removed from the AT command set, because a telnet remote login session should not be started with this function enabled.

Binary mode considerations

Binary operation is available for telnet but only as a telnet escape command. Requesting binary mode does not guarantee that it can be established because the option is negotiated with the remote host. Query telnet status after requesting binary mode to determine this, but do so with caution.

Software flow control cannot be used since XON/OFF characters in the data stream can not be distinguished from data with the same bit format. Also, escape data streams containing the telnet escape command character should be escaped by doubling the character. For example, if the escape character is ^^ (decimal 30) and it appears in the binary data stream, then modify the data by inserting a second escape character adjacent to the first, for example:

NOTE: Telnet servers are usually quite slow, so be patient when waiting for the CONNECT message, and again for the login screen. Usually, after the LOGIN session operations speed up.

Follow the instructions from the server to run and terminate your session. Usually, when you quit the telnet session the server breaks the connection and a NO CARRIER message appears. If this does not happen, escape from online mode with the +++ escape sequence and hang up with an ATH0.

1. Original data stream

• Data to modem [...69,123,24,30,49,....]

• Data from modem [...69,123,24,49,....]

2. Modified data

• Data to modem [...69,123,24,30,30,49,....]

• Data from modem [...69,123,24,30,49,....]

If binary data transfer is needed, the telnet mode of operation is probably not the appropriate mechanism to use. The need to negotiate the option, and the need for doubling the telnet escape character tend to make the function awkward. Non-telnet modes such as UDP or TCP are much better suited to binary data transfer.

Telnet operation

When the setup options are complete (\O1, \F0, \M1, \T0 are recommended) establish a telnet session by dialing a telnet server, for example, a bulletin board with an ATDTn.n.n.n/p command; where n.n.n.n is the IP Address of the telnet server. The port number (p) is not required because it defaults to the standard telnet port number (23).

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6 Device Attachment

DTE

RS-232 connection

The DART 200 has an RS-232 DB9 interface. If the remote device has a similar interface, then any standard PC communications cable functions as a connector between the two. Otherwise, refer to Data and control interface, p. 8-14, for a discussion of the RS-232 leads and the minimum number required for operation.

Standard RS-232 communications cables function properly for distances up to 50 feet. If longer lengths are required, low loss RS-232 cable or electronic cable extenders can be used; both are available from local cable distributors or electronic catalogs.

Null modem function

The RS-232 interface specification was defined before the invention of microcomputers. The original intent was to standardize the method that computers and terminals used to communicate remotely over telephone lines. The standard specification is generalized in Figure 6-1.

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Figure 6-1. Standard RS-232 connection

DTE

Terminal

Computer

RS-232

DCE DCE

Modem

Phone

Line

Modem

RS-232

The RS-232 standard specified the label Data Terminal Equipment or Data Terminating Equipment (DTE) for terminals and computers, and the label Data Communications Equipment (DCE) for modems. The popularization of RS-232 serial communications resulted in many different types of equipment, besides modems, that employ the standard. Many manufacturers expect devices to connect directly to DTE equipment (usually, PCs). Consequently, devices are designed with a DCE interface, so a standard RS-232 cable meets the cabling requirements. Common usage of RS-232 is shown in Figure 6-2.

DART 200 CDPD Modem User’s Guide 6 Device Attachment

DTE

DCE

Figure 6-2. Stand-alone RS-232

Computer

RS-232

Terminal

The problem with this occurs when modems are inserted between the DTE and a remote device with a DCE interface. The modem expects to communicate with a DTE interface. Since this is not the case at the remote end, where the DCE modem is trying to talk to a DCE device, a communications failure results. The solution for this situation is a null modem connector. A typical null modem pin out is shown in Table 6-1.

Table 6-1. Typical null modem pinout

Female DB9

1 DCD 4 2 RXD 3 3 TXD 2 4 DTR 6 and 1 5 SGD 5 6 DSR 4 7 RTS 8 8 CTS 7 9 --- Open

Male DB9

The null modem adapter corrects the mismatch between the modem and a terminating device having a DCE interface. The proper location for the null modem is shown in Figure 6-3.

Figure 6-3. Null modem location

DTE

Computer

RS-232

DCE DCE

Modem

Phone

Modem

Line

RS-232

Null modem needed here

DCE

Terminal

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To identify this problem connect a PC directly to the device and establish communication. If communication is established, the device uses a DCE interface and requires a null modem to communicate with the DART

200. Null modem adapters are available as stand-alones; that look like an

RS-232 gender-changer, or as null modem cables. Null modem adapters are available from electronics stores and are well suited for application development. Null modem cables can be ordered from cable suppliers, and are better suited for field deployment, because the cables eliminate the extra part and failure prone connections required for a stand-alone null modem.

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7 Vehicle Installation

Considerations

Electrical transients

When a Data Access Radio Transceiver (DART) 200 is installed in a vehicle it is usually powered from the vehicle’s electrical system. Transients or temporary outages that can occur during starts or other vehicle operations, can cause the DART 200 to reset the power. These transients can also impact the attached Mobile Application Subsystem (MAS).

There are several options available to minimize or eliminate vehicle power disturbances, including filters, cut off switches, and universal power supplies. The best solution; however, is to compare the needs of the application and equipment to the cost of the proposed solution. Try alternatives during testing to avoid problems during application roll out.

The simplest power backup system is a 12-volt battery; large enough to supply the modem’s maximum transmit current, with a blocking diode to prevent discharging the battery into the vehicle’s electrical system. The battery floats on the vehicle’s 12 volt DC power system, constantly being recharged, and used only during periods of transient voltage drop. The diode prevents the vehicle’s electrical system from drawing power from the backup battery during these voltage drops.

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The diode needs to allow at least 2.5 amps of current in the forward direction, and withstand a reverse voltage of at least 20 volts. Higher rated diodes, available at a nominal cost from electronic stores, dealers, and catalogs, provide a better safety factor.

Application considerations

Resets can occur during or between communications with the remote system. The most serious situation occurs if the reset happens during communications, because the modem switches from online to command mode. If the reset occurs between communications, the impact can be less critical because many applications take the modem out of online mode during this time period anyway.

DART 200 CDPD Modem User’s Guide 7 Vehicle Installation Considerations

The application program in the MAS has no way of knowing before attempting a send or receive operation if the modem is still in online mode. The application can be designed to assume that the modem is always online, or to always check that it is online before performing the send or receive operation. In the former case, a send operation failure is indicated by an error return code (in command mode the modem expects to see all messages start with an AT), while a receive failure is indicated by a timeout.

If the MAS can sense the RS-232 interface, as described in CDPD status sensing, p. 8-15, perform this operation to verify that the modem is still connected before attempting a send/receive operation. For Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) the connected state implies that the modem is online. If the MAS cannot sense the interface leads, it tries the send/receive operation first, and only proceeds to error-checking if an error or timeout occurs.

For applications using Serial Line Internet Protocol (SLIP), use the Automatic SLIP restart feature on the modem, to automatically put the modem back into SLIP mode following a power reset.

If the modem is not online, the next step is to check registration state through the RS-232 leads or with ATS57? If it is not registered, the program waits and periodically checks registration status, eventually proceeding when the modem reregisters. It is assumed that the modem is set up to register automatically, as described in Auto-Registration when not registered, p. 8-7.

When the modem becomes registered, the next step depends on whether or not the MAS is a server or a client. If it is a client, the recovery procedure for both TCP and UDP is to issue the appropriate dial command. If it is a server, the recovery procedure for both TCP and UDP is to wait for a call from a client.

Proximity to other antennas

In general, do not locate the DART 200 antenna closer than 5 feet to other antennas (specifically, two-way radio antennas) and in certain cases more separation is required. In many vehicular applications, there are two-way radio transmitters in use and usually the antenna mountings are not 5 feet apart. Interference from the radio transmitter can slow down response times or block modem transmission.

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In this situation, separate the antennas as far as possible and then run a field test when the two-way radio is also being used. If the DART 200 works satisfactorily you do not have a problem, but if it does not filtering is required. A bandpass filter on the two-way radio’s transmitter output eliminates harmonics that can interfere with the cellular frequencies. A band reject filter on the DART 200’s input, centered on the two-way radio’s base frequency, provides signal attenuation at that frequency to help prevent de-sensing the DART 200’s Radio Frequency (RF) circuitry: either, or both can be required. The calculation to determine the filtering usually requires an RF engineer.

If you do not have the option to field test, then the theoretical calculation approach is your only option.

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8 Application Programming

Chapter

The Data Access Radio Transceiver (DART) 200 offers built-in Transmission Control Protocol (TCP), User Datagram Protocol (UDP), Serial Line Internet Protocol (SLIP), and telnet support, but most end-user application programming that interacts with the modem uses TCP, UDP, or SLIP.

Telnet is used primarily as a path to applications on remote hosts with the local device being an ASCII terminal or, more likely, a PC emulating an ASCII terminal. Outside of setting up the modem initially to meet telnet’s needs, there is no programming to do. Error handling is provided by the ASCII terminal emulator and is usually minimal.

This chapter is directed at TCP and UDP applications, and DART 200 solutions, particularly for DART 200 error handling. SLIP mode applications function similarly, but the specifics are a function of the capabilities of the software stack being used. If you plan on using SLIP, refer to the application programming guide for your specific package.

AT Command Set Support

The terminal device, (Mobile Application Subsystem), does not have to support the Attention (AT) command set directly to operate with the DART 200. Even in cases where the device does support the basic AT command set, there are some extensions to the command set that are not supported. Usually, a programmable device can create a constant string that represents the desired AT command. Sending such a character string to the DART 200 works the same as sending the AT command.

If the remote device is of limited intelligence it does not need to support the AT command set at all. The modem can be pre-initialized to work with the remote device, including being in auto answer mode. In auto answer mode, when the modem receives a connection request (TCP mode), or a datagram (UDP mode), it goes online and passes data to the attached device, just like a wire-line modem. In this situation, the fact that CDPD is the communications medium is transparent to the remote device.

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Device drivers

The DART 200 requires no special device drivers. Serial communications port support provided by the PC Operating System is all that is needed. For modem setup any ASCII terminal emulator, such as Terminal, Hyperterminal, Procomm, Kermit, and so on, is appropriate. For applications use the normal communications port I/O commands supported by the programming language you use.

Application program structure

A CDPD application is similar in general structure to most network based applications. It consists of the following major sections:

DART setup

This is usually done before the DART 200 is put into use, or as a special, first time only function of the application. The needs of the application and the terminal are evaluated based on the protocol being used (TCP, UDP, or SLIP mode) and the appropriate options are chosen. Refer to Chapter 5, DART Supported Protocols, for modem setup samples.

Network connection

Establishing a network connection involves, enabling the Personal Identification Number (PIN) (if used), registering the modem with the network (if not set up to register automatically), then establishing the communication session with a peer device, as follows:

1. If PINs are used, issue the PIN enabling command (AT*E) before

attempting to access the network.

2. For application use (as opposed to testing), set up the modem

registration as fully automatic, by setting the Registration time-out S-Register to 0 (ATS13=0), then issue an AT\R4 command, as described in Automatic registration, p. 8-6. Save your changes with an AT&W.

This causes the DART 200 to automatically register at power up, and when registration is dropped, for example, due to a power failure or driving out of the coverage area.

3. A session is established for a client by dialing (ATDn command) to

establish a logical connection with another device (TCP), or to set up the target device’s IP Address and port for insertion into the data packets to follow (UDP). Refer to the D command in Appendix F,

DART AT Command Set, for more information.

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4. For a modem functioning as a server, (answering calls or being

polled) activate the appropriate server, TCP (with AT*A1) or UDP (with AT*A2). The connection can be established automatically by having auto answer active (S-Register 0 =1), or manually by issuing an ATA command when the RING message occurs, as described in Auto Answer setup, p. 8-11.

For both client and server systems, successful completion of the Dial command (ATD) is indicated by a CONNECT message (verbose mode) or a 1 (terse mode). This puts the modem in online mode. In this state, AT commands are ignored, the autobaud function is suppressed, and flow control (if specified) is enabled.

Data transfer

To accomplish data transfer, the DART 200 must be in online mode. Data transfer is performed by the Mobile Application Subsystem (MAS) by sending data to or reading data from the DART 200’s RS-232 serial port. Unlike the previous activities, data transfer uses device-specific rather than AT commands. For a PC the I/O commands are directed to the serial port and use the serial port I/O driver supplied by the operating system being used.

Outgoing data accumulates in the DART 200 until a data forwarding condition is reached. The DART 200 then attaches the appropriate header information, and sends the data onto the CDPD network for forwarding through the appropriate routers to the target IP Address and port. Refer to Data forwarding, p. 8-8, for more details.

The incoming packet is received by the DART 200, and the header is removed, and the data passed, subject to flow control considerations, as described on p. 8-12, to the attached device.

Modes of operation

A major difference between a Cellular Digital Packet Data (CDPD) Hayes-compatible network session and a typical synchronous communications session is the two modes of operation: command mode and online (data) mode.

AT commands are issued and responded to by the DART 200 when in command mode. Once a remote station is dialed, or SLIP mode is started, the modem enters online mode and only transmits or receives data; it no longer responds to AT commands.

To return to command mode, to process AT commands for error recovery purposes or to hang up at the end of a session, the DART 200 issues an escape sequence, or drops Data Terminal Ready (DTR) (if possible) with an &Dn set up option specified. Refer to Escaping

through the control interface, p. 8-16 for details.

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Error recovery

Good application design includes provisions for handling errors. Insert code to perform the error-handling function after every operation where an error might occur, such as after every AT command, where the most likely failure is modem power loss, and after every communications operation where these five distinct errors are possible:

1. Loss of modem power.

2. Loss of radio signal.

3. Loss of network registration.

4. Loss of host connection (does not apply to UDP).

5. Loss of online mode (a power reset has occurred). Failure of a communications operation (usually send or receive) is

indicated by:

• Send - A time out or an error response

• Receive - A time out

If the MAS is capable of sensing signal status over the RS-232 interface then testing for loss of signal, registration, or connection can be done (if desired) before attempting the send/receive operation. If it is not (or the application designer chooses not to sense prior to I/O operations), then testing follows failures only.

There is no specific test for loss of modem power. If the modem is in online mode, and the application does not get an OK or 0 response to the escape sequence, then power loss can be assumed. Similarly, if the modem is in command mode and the application fails to get the expected response to an AT command, then power loss can be assumed.

Status information and error codes, to be analyzed to determine appropriate error recovery actions, can be obtained from the Data Set Ready (DSR) and Data Carrier Detect (DCD) signals, or from Status (S-)Registers 56, 57, 62, 63, 101, 102 and 126. The use of DSR and DCD for basic status sensing is recommended (if the MAS supports it) for both speed and simplicity. The available information, by source, is summarized below.

• DCD - This signal can be set up at modem initialization time to

follow the state of the connection established condition (&C1), the state of the RF in range condition (&C3), or the modem’s registration state (&C4). The default is &C1

• DSR - This signal can be set up at modem initialization time to

follow the state of the connection established condition (&S1), the state of the RF in range condition (&S2), or the modem’s registration state (&S3). The default is &S0 (always active)

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DART 200 CDPD Modem User’s Guide 8 Application Programming

With three variables and only two signal lines, decide which two of the three items are most crucial to the application. Usually, RF in range and registration state are tracked. If both of these statuses are present, then a Dial command (ATD) can be issued. To determine more than two items of status the MAS escapes to command mode and reads the network status register (S-Register 57).

• DTR (Data Terminal Ready) - Transitioning this signal lets the

application enter command mode without having to use the escape sequence. To do this, the &D1 (escape) or &D2 (escape and hang-up) option must be selected at initialization time. If this option is used DTR must be held in the down state for a minimum of 15 ms. Refer to Escaping through the control interface, p. 8-16, for more information. The default is &D0 (ignore DTR)

• S-Register 56 (extended network error codes) - Indicates reasons for

a registration failure. Codes 1-7 are suggested in the CDPD specifications but may not be followed by all carriers or infrastructure providers.

1 Registration denied - Network Entity Identifier (NEI) may

be in use by another device 2 Service currently not available 3 Invalid NEI (IP Address) 4 Insufficient authentication credentials 5 Authentication credentials not supported 6 NEI has exceeded usage limitations 7 Service denied on this subnetwork; try an alternate Provider 250 Timed out waiting for home Mobile Data Intermediate

Station (MDIS) registration response 251 Mobile Data Link Protocol (MDLP) parameters unsupported 252 MDLP version unsupported 254 Could not access the CDPD network 255 Could not de-register the NEI because it was not registered

• S-Register 57 (network status) - A bit-mapped register showing

several items of interest. For error-handling the values of interest are:

• RF in range - value of 128 or greater (bit 7)

• Registered - odd value (bit 0)

• Connected - value of 133, 165, 197 or 229 (bit 2 and not bit 3)

• S-Register 62 (connection failure) - This register indicates at what

point in the operation the connection failed 1 During the connection process

2 During the transmission of a packet 3 During the reception of a packet

• S-Register 63 (connection failure) - This register indicates the most

probable cause for the connection failure or loss of connection 24 No socket available

67 Address already in use 69 Network is down

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DART 200 CDPD Modem User’s Guide 8 Application Programming

70 Network is unreachable 71 Network dropped connection or reset 72 Software caused connection abort 73 Connection reset by peer 75 Socket is already connected 76 Socket is not connected 78 Connection timed out 79 Connection refused (for DART to DART the server function is

not active or is of the wrong type) 81 Host is down 82 Host is unreachable

• S-Register 101 (CDPD available flag) - Indicates not only if the

modem acquired a channel, but also whether it established (or reestablished) CDPD communications with the MDIS. This is a better indicator than the RF in range bit found in S-Register 57

0 CDPD not available 1 CDPD available

• S-Register 102 (mean Receive Signal Strength Indication for

acquired channel) - Indicates the RF signal strength in dBm for the active channel. If CDPD is not currently available (S-Register 101 =

0), this value has no meaning A negative value usually in the range of -50 to -113dBm. Values

below -100 are unreliable, and below -110 cannot be used.

• S-Register 126 (Registration progress status) - Indicates how far

through the registration process the modem proceeded 0 Protocol not active

1 Temporary Equipment Identifier (TEI) assignment pending 2 Link connection establishment pending - waiting for

Unnumbered Acknowledgement (UA) 3 Encryption key exchange pending - waiting for MDIS Key

Exchange (IKE) 4 Registration pending - waiting for Intermediate System

Confirmation (ISC) 5 Registration complete

Use the ATSn? command to read the S-Registers with the modem in command mode

After sensing the appropriate registers, if the MAS determines it needs to go back to online mode, it issues an ATO command (TCP or UDP), or AT*S command (SLIP) to do so.

Automatic registration

Before the DART 200 can operate on the CDPD network it must be registered. Registration is controlled by the AT\Rn command; the following options are available:

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Sierra Wireless DART 200 CDPD User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual