Symbol Spectrum24 AP-3020 Reference Manual

Spectrum24

Access Point AP-3020

Product Reference Guide

PRE-RELEASE

70-20504-02

April 1999

www.symbol.com

Copyright

Copyright © 1999 by Symbol Technologies, Inc. All rights reserved.
No part of this publication may be modified or adapted in any way, for any purposes without permission in writing from Symbol. The material in this manual

is subject to change without notice.
Symbol reserves the right to make changes to any product to improve reliability, function, or design.
No license is granted, either expressly or by implication, estoppel, or otherwise under any Symbol Technologies, Inc., intellectual property rights. An implied

license only exists for equipment, circuits, and subsystems contained in Symbol products.
Symbol, the Symbol logo and Spectrum24 are registered trademarks of Symbol Technologies, Inc.
Other product names mentioned in this manual may be trademarks or registered trademarks of their respective companies and are hereby acknowledged.
Novell and LAN Workplace are registered trademarks of Novell Inc.

Patents

This product is covered by one or more of the following U.S. and foreign Patents:
U.S. Patent No.4,360,798; 4,369,361; 4,387,297; 4,460,120; 4,496,831; 4,593,186; 4,603,262; 4,607,156; 4,652,750; 4,673,805; 4,736,095;

4,758,717; 4,816,660; 4,845,350; 4,896,026; 4,897,532; 4,923,281; 4,933,538; 4,992,717; 5,015,833; 5,017,765; 5,021,641; 5,029,183;
5,047,617; 5,103,461; 5,113,445; 5,130,520 5,140,144; 5,142,550; 5,149,950; 5,157,687; 5,168,148; 5,168,149; 5,180,904; 5,229,591;
5,230,088; 5,235,167; 5,243,655; 5,247,162; 5,250,791; 5,250,792; 5,262,627; 5,262,628; 5,266,787; 5,278,398; 5,280,162; 5,280,163;
5,280,164; 5,280,498; 5,304,786; 5,304,788; 5,306,900; 5,321,246; 5,324,924; 5,337,361; 5,367,151; 5,373,148; 5,378,882; 5,396,053;
5,396,055; 5,399,846; 5,408,081; 5,410,139; 5,410,140; 5,412,198; 5,418,812; 5,420,411; 5,436,440; 5,444,231; 5,449,891; 5,449,893;
5,468,949; 5,471,042; 5,478,998; 5,479,000; 5,479,002; 5,479,441; 5,504,322; 5,519,577; 5,528,621; 5,532,469; 5,543,610; 5,545,889;
5,552,592; 5,578,810; 5,581,070; 5,589,679; 5,589,680; 5,608,202; 5,612,531; 5,619,028; 5,664,229; 5,668,803; 5,675,139; 5,693,929;
5,698,835; 5,705,800; 5,714,746; 5,723,851; 5,734,152; 5,734,153; 5,745,794; 5,754,587; 5,658,383; D305,885; D341,584; D344,501;
D359,483; D362,453; D362,435; D363,700; D363,918; D370,478; D383,124; D391,250.

Invention No. 55,358; 62,539; 69,060; 69,187 (Taiwan); No. 1,601,796; 1,907,875; 1,955,269 (Japan).
European Patent 367,299; 414,281; 367,300; 367,298; UK 2,072,832; France 81/03938; Italy 1,138,713.

Symbol Technologies, Inc.

One Symbol Plaza

Telephone:(800)SCAN234, [phone], TLX:6711519

Holtsville, N.Y. 11742-1300

www.symbol.com

ii Spectrum24 Access Point AP-3020 Product Reference Guide

About This Document

This document covers...and has the following sections:

• ...

• ...

• ...

Reference Documents

This reference guide refers to the following documents:

Part Number Document Title

70-xxxxx-01 Title

RFCs (Request For Comments) can be found on the Web at: http://www.ctrl-c.lin.se/ftp/DOC/RFC.

Conventions

Keystrokes are indicated as follows:
ENTER identifies a key.
FUNC, CTRL, C identifies a key sequence. Press and release each key in turn.
Press A+B press the indicated keys simultaneously.

Hold A+B press and hold the indicated keys while performing or waiting for another

function. Used in combination with another keystroke.

Typeface conventions used include.
<angles> indicates mandatory parameters in a given syntax.

[brackets] for command line, indicates available parameters; in configuration files

brackets act as separators for options.

GUI Screen text indicates the name of a control in a GUI-based application.

Italics indicates the first time a term is used, a book title, variables, and menu titles.

Spectrum24 Access Point AP-3020 Product Reference Guide iii

Screen

indicates monitor screen dialog. Also indicates user input. A screen is
the hardware device on which data appears. A display is data arranged
on a screen.

Terminal indicates text shown on a radio terminal screen.

This document uses the following for certain conditions or types of information:

Indicates tips or special requirements.

Indicates conditions that can cause equipment damage or data loss.

Indicates a potentially dangerous condition or procedure that only Symbol­trained personnel should attempt to correct or perform.

iv Spectrum24 Access Point AP-3020 Product Reference Guide

Contents

Chapter 1 Introduction............................................................................................1

1.1 Ethernet Access Point (AP) ............................................................... 1

1.1.1 New Features ...................................................................... 3

1.2 Radio Basics .................................................................................. 3

1.2.1 S24 Network Topology......................................................... 4

1.2.2 Quick Wireless AP Setup ...................................................... 8

1.2.3 Cellular Coverage ............................................................... 9

1.2.4 Site Topography ................................................................ 12

1.3 Advanced Radio Theory................................................................ 12

1.3.1 MAC Layer Bridging........................................................... 13

1.3.2 Auto Fallback to Wireless Mode.......................................... 15

1.3.3 DHCP Support................................................................... 15

1.3.4 Media Types......................................................................16

1.3.5 Bridging Support................................................................17

1.3.6 Frequency Hopping Spread Spectrum ................................. 21

1.3.7 MU Association Process...................................................... 23

1.3.8 Mobile IP (Roaming Across Routers) ................................... 26

1.3.9 Supporting CAM and PSP Stations.......................................28

1.3.10 Data Encryption...............................................................29

1.3.11 HTTP, HTML Web Server Support...................................... 30

1.3.12 Management Options ......................................................31

Chapter 2 Configuring the AP............................................................................. 35

2.1 Gaining Access to the UI .............................................................. 35

2.1.1 Using Telnet ......................................................................35

2.1.2 Using a Direct Serial Connection ........................................ 36

2.1.3 Using a Dial-Up Connection .............................................. 38

2.1.4 Using a Web Browser.........................................................38

2.2 Navigating the UI......................................................................... 45

Spectrum24 Access Point AP-3020 Product Reference Guide v

2.2.1 Entering Admin Mode ........................................................... 47

2.2.2 Changing the Access to the UI ...............................................48

2.2.3 Configuring for Dial-Up to the UI .......................................... 49

2.2.4 Navigating the UI Via a Web Browser .................................... 50

2.3 Access Point Installation...................................................................51

2.4 Configuring System Parameters .......................................................53

2.5 Configuring Radio Parameters .........................................................58

2.5.1 Wireless Operation Parameters..............................................63

2.6 Configuring PPP .............................................................................. 67

2.6.1 PPP Direct............................................................................. 67

2.6.2 Establishing Connection ........................................................ 68

2.6.3 PPP with Modems.................................................................. 68

2.6.4 Originating AP...................................................................... 68

2.6.5 Answering AP ....................................................................... 69

2.6.6 Initiating Modem Connection.................................................70

2.7 Configuring the SNMP Agent ...........................................................70

2.8 Configuring the ACL........................................................................74

2.8.1 Range of MUs....................................................................... 74

2.8.2 Adding Allowed MUs.............................................................76

2.8.3 Removing Allowed MUs......................................................... 76

2.8.4 Enable/Disable the ACL ........................................................ 77

2.8.5 Removing All Allowed MUs.................................................... 77

2.8.6 Load ACL from MU List .........................................................77

2.9 Configuring Address Filtering........................................................... 78

2.9.1 Adding Disallowed MUs ........................................................ 79

2.9.2 Removing Disallowed MUs .................................................... 79

2.10 Configuring Type Filtering ............................................................. 79

2.10.1 Adding Filter Types ............................................................. 79

2.10.2 Removing Filter Types.......................................................... 79

2.10.3 Controlling Type Filters........................................................80

2.11 Clearing MUs from the AP ............................................................. 80

vi Spectrum24 Access Point AP-3020 Product Reference Guide

2.12 Setting Logging Options ................................................................80

2.13 Manually Updating AP Firmware.................................................... 82

2.13.1 Updating using TFTP...........................................................82

2.13.2 Updating using Xmodem..................................................... 85

2.14 Auto Upgrade all APs Via Messaging.............................................. 88

2.15 Performing Pings........................................................................... 90

2.16 Mobile IP Using MD5 Authentication .............................................. 94

2.17 Saving the Configuration ...............................................................95

2.18 Resetting the AP ............................................................................ 96

2.19 Restoring Configuration................................................................. 96

Chapter 3 Monitoring Statistics...........................................................................97

3.1 System Summary............................................................................. 97

3.2 Interface Statistics.......................................................................... 100

3.3 Forwarding Counts........................................................................ 102

3.4 Mobile Units ................................................................................. 102

3.5 Mobile IP ......................................................................................107

3.6 Known APs.................................................................................... 108

3.7 Ethernet Statistics........................................................................... 110

3.8 Radio Statistics ..............................................................................112

3.9 Miscellaneous Statistics..................................................................120

3.9.1 Analyzing Frequency Use .................................................... 122

3.9.2 Analyzing Retries................................................................. 123

3.10 Event History...............................................................................124

3.11 Clearing Statistics........................................................................ 125

Chapter 4 Hardware Installation ...................................................................... 127

4.1 Precautions................................................................................... 127

4.2 Package Contents ......................................................................... 127

4.3 Requirements................................................................................ 128

4.3.1 Network Connection ........................................................... 128

4.3.2 10Base-T UTP..................................................................... 129

4.3.3 Single Cell.......................................................................... 129

Spectrum24 Access Point AP-3020 Product Reference Guide vii

4.4 Attaching the Antenna(s)................................................................130

4.4.1 Antenna Extension Cables ................................................... 131

4.5 Power Options ..............................................................................131

4.6 Mounting the AP ...........................................................................132

4.7 Connecting the Power Adapter.......................................................132

4.8 LED Indicators............................................................................... 133

4.8.1 WLAP mode LED display. .................................................... 134

4.9 Troubleshooting ............................................................................ 136

4.9.1 Ensure wired network is operating........................................136

4.10 Setting Up MUs...........................................................................138

Appendix A Specifications..................................................................................A - 1

A.1 Physical Characteristics.................................................................A - 1

A.2 Radio Characteristics....................................................................A - 2

A.3 Network Characteristics................................................................A - 3

Appendix B Supported Modems....................................................................... B - 1

Appendix C Customer Support........................................................................ C - 1

Appendix D Regulatory Compliance .............................................................. D - 1

viii Spectrum24 Access Point AP-3020 Product Reference Guide

Chapter 1 Introduction

Spectrum24 is a frequency-hopping, spread spectrum cellular network that
operates between 2.4 and 2.5 GHz (gigahertz). This technology provides
a high-capacity network using multiple access points within large or
small environments.

Spectrum24 features include:

• bridging architecture to provide communication between radio and
wired multiple network segments

• a design based on the IEEE 802.11 standard

• a 2 Mbps data rate for fast operation

• seamless roaming for mobile users with devices such as laptop
computers, wireless PCs, scanning terminals and computer devices with
PCMCIA slots.

1.1 Ethernet Access Point (AP)

The Ethernet Access Point (AP) provides a bridge between Ethernet wired
LANs and Spectrum24 wireless networks. It provides transparent access
between Ethernet wired networks and radio-equipped mobile units (MUs).
MUs include the full line of Symbol Spectrum24 terminals, scanners, third­party devices and other devices.

The AP provides 1 and 2 Mbps data transfer rate on the radio network.
It monitors Ethernet traffic and forwards appropriate Ethernet messages to
MUs over the Spectrum24 network. It also monitors MU radio traffic and
forwards MU packets to the Ethernet LAN.

The AP meets the following:

• the regulatory requirements for Europe and many other areas of
the world

• FCC part 15, class A with no external shielding

• FCC part 15 class B, ETS 300-339 compliance, including CE mark.

Spectrum24 Access Point AP-3020 Product Reference Guide 1

Introduction

The AP has the following features:

• built-in diagnostics including a power-up self-check

• a four-way bridging architecture (wireless, Ethernet, PPP, internal stack)

• wireless MAC interface

• 10baseT Ethernet port interface with full-speed filtering

• 100 mW and 500 mW radio versions

• power supply IEC connector and a country-specific AC power cable

• PC/AT Serial Port Interface

• built-in antenna diversity

• multiple antenna options

• support for 127 mobile units

• SNMP support

• wireless AP support

• repeater functions.
An MU communicating with an AP appears on the network as a peer to

other network devices. The wireless interface is transparent. The AP receives
data from its wired or wireless interfaces and forwards the data to the
proper interface.

The AP has connections for the wired network, external antennas and
power supply. The AP attaches to a wall or ceiling depending on installation­site requirements.

The AP requires a single antenna for radio transmission and reception.
The dual-antenna system allows the AP to select the best radio signal.

2 Spectrum24 Access Point AP-3020 Product Reference Guide

1.1.1 New Features

• IEEE 802.1d Spanning Tree Support

• Auto-Fallback to Wireless Mode

• Increased MIB support

• DHCP Support

• HTTP, Web server Support

• Mobile IP Support

• Programmable SNMP Trap Support using SNMP Agents

• Data Encryption

• Wireless Options in Radio Parameters

• ACL (Access Control List)

• AP Auto Upgrade of other APs via messaging

• Multiple Gateways.

1.2 Radio Basics

Spectrum24 uses electromagnetic waves, radio signals, to transmit and
receive electric signals without wires. Users communicate with the network by
establishing radio links between terminals and APs.

Introduction

Spectrum24 uses FM (frequency modulation) to transmit digital data from
one device to another. Using FM, a radio signal begins with a carrier signal
that provides the base or center frequency. The digital data signal is
superimposed on the carrier signal (modulation). The radio signal
propagates into the air as electromagnetic waves. A receiving antenna in the
path of the waves absorbs the waves as electrical signals. The receiving
device demodulates the signal by removing the carrier signal. This
demodulation results in the original digital data.

Spectrum24 uses the environment (the air and certain objects) as the
transmission medium. Spectrum24 radio devices use the 2.4 to 2.5-GHz
frequency range, a license-free range throughout much of the world. The
actual range is country-dependent.

Spectrum24 Access Point AP-3020 Product Reference Guide 3

Introduction

Spectrum24 devices, like other Ethernet devices, have unique, hardware­encoded Media Access Control (MAC) or IEEE addresses. MAC addresses
determine the device sending or receiving data. The MAC address is a 48-bit
number written as six hexadecimal bytes separated by colons. For example:

00:A0:F8:24:9A:C8

To locate the AP MAC address see the bottom of the unit.

1.2.1 S24 Network Topology

The variations possible in Spectrum24 network topologies depend on the
following factors:

• the AP function in the network

• a 1 or 2 Mbps data transfer rate

•the wireless AP (WLAP) interface.

A WLAP communicates only with its root AP through the wireless interface as
discussed in The Root AP and Association Process on page 14.

4 Spectrum24 Access Point AP-3020 Product Reference Guide

Introduction

If the AP is not in wireless mode, select from the following topologies:

• A single AP used without the wired network provides a single-cell wireless
network for peer-to-peer MUs.

• A single AP can bridge the Ethernet and radio networks.

• Multiple APs can coexist as separate, individual networks at the same site
without interference using different Net_IDs.

Spectrum24 Access Point AP-3020 Product Reference Guide 5

Introduction

• Multiple APs wired together provide a network with better coverage area
and performance.

• Multiple 1 Mbps and 2 Mbps APs wired together.

6 Spectrum24 Access Point AP-3020 Product Reference Guide

In WLAP mode, a wireless AP-to-AP connection functions:

• as a bridge to connect two Ethernet networks

Introduction

• as a repeater to extend coverage area without additional
network cabling

Spectrum24 Access Point AP-3020 Product Reference Guide 7

Introduction

When using a wireless AP-to-AP connection, use the optimal antenna
configuration for the site. For example, use a directional antenna when
establishing a dedicated wireless bridge or repeater.

• A wireless AP network is possible, depending on the network bandwidth
and configuration. Each wireless AP can have connections with up to
four other wireless APs.

Using more than two WLAPs to establish a connection slows network
performance for all topologies. If not using the AP Auto Configure feature,
disable WNMP Functions and AP-AP State Xchg parameters under the Set
System Configuration screen to increase WLAP performance.

WNMP is a Wireless Network Management Protocol.

1.2.2 Quick Wireless AP Setup

To set up an AP for wireless operation automatically, select the Enabled
option for the WLAP Mode parameter. To set these values, See 2.5

Configuring Radio Parameters on page 43.

The WLAP initialization process length depends on the time specified in the
WLAP Forward Delay field. See 2.5 Configuring Radio Parameters on page

43.

8 Spectrum24 Access Point AP-3020 Product Reference Guide

1.2.3 Cellular Coverage

The AP establishes an average communication range with MUs called a
Basic Service Set (BSS) or cell. When in a particular cell the MU associates
and communicates with the AP of that cell. Each cell has a Basic Service Set
Identifier (BSS_ID). In 802.11, the AP MAC address represents the BSS_ID.

The MU recognizes the AP it associates with using the BSS_ID. Adding APs to
a LAN establishes more cells in an environment, making it an RF Network
using the same Net_ID or Extended Service Set (ESS).

Introduction

APs with the same Net_ID (ESS) define the coverage area. The MU searches
for APs with a matching Net_ID (ESS) and synchronizes with an AP to
establish communications. This allows MUs within the coverage area to move
about or roam. As the MU roams from cell to cell, it switches APs. The switch
occurs when the MU analyzes the reception quality at a location and decides
the AP to communicate with based on the best signal strength and lowest MU
load distribution.

If the MU does not find an AP with a workable signal, it performs a scan to
find any AP. As MUs switch APs, the AP updates the association table.
Roaming is transparent in high-level applications.

Spectrum24 Access Point AP-3020 Product Reference Guide 9

Introduction

The user can configure the Net_ID (ESS). A valid Net_ID (ESS) is an
alphanumeric, case-sensitive identifier up to 32 characters. Ensure all nodes
within one LAN use the same Net_ID (ESS) to communicate on the same
LAN. Multiple wireless LANs can coexist in a single environment by assigning
different Net_IDs (ESS) for APs.

The Root AP and Association Process

By default, APs with WLAP Mode enabled and within range of each other
automatically associate and configure wireless operation parameters at
power up. This association process determines the wireless connection
viability and establishes the Root AP and subsequently designated WLAPs.

APs communicating wirelessly together require the same Net_ID (ESS) setting.

The root AP maintains the wireless connection among WLAPs by sending out
beacons, sending and receiving configuration BPDU (Bridge Protocol Data

Unit) packets between each designated WLAP. The WLAP with the lowest
WLAP ID becomes the Root AP. The WLAP ID is a concatenation of the WLAP
Priority value and the MAC address. Ensure the WLAPs associated with the
Root AP use the Root AP hop sequence, DTIM (Delivery Traffic Indicator
Maps) and TIM (Traffic Indicator Message) interval.

10 Spectrum24 Access Point AP-3020 Product Reference Guide

Introduction

In this configuration, the WLAP Priority value is the default 8000 Hex. On
concatenating this value to the MAC addresses of the APs, AP A on Ethernet I
has the lowest WLAP ID with 800000A0F800181A, making it the Root AP. AP
C uses the AP A hop sequence, DTIM and TIM interval.

If AP D on Ethernet II has data for a device on Ethernet I, it requires a bridge
or a repeater. In this configuration, AP C functions as a repeater. To ensure
transmission to devices on Ethernet I, AP D has to use the AP A hop
sequence, DTIM and TIM interval.

To prevent forming a loop, disable WLAP mode on B and E. See 2.5

Configuring Radio Parameters on page 43.

To manually designate AP B as the Root AP, assign it a lower WLAP Priority
value. See 2.5 Configuring Radio Parameters on page 43. Assigning a WLAP
Priority value of 7000 Hex to the AP B MAC address of
00:A0:F8:11:23:5D causes AP B to become the Root AP by having the
lowest WLAP ID of 700000A0F811235D.

802.1d Spanning Tree Support

This protocol creates a loop-free topography with exactly ONE path between
every LAN. This is the shortest path from the Root AP to each AP and LAN. If
an AP or LAN fails, a new route is calculated and added to the tree. All
packet forwarding follows the spanning tree. APs have to choose one AP as
the Root AP. The same holds true for WLAPs associating with the root AP or
another AP connected to the Ethernet LAN to prevent forming loops.

Spectrum24 Access Point AP-3020 Product Reference Guide 11

Introduction

1.2.4 Site Topography

For optimal performance, locate MUs and APs away from transformers,
heavy-duty motors, fluorescent lights, microwave ovens, refrigerators and
other industrial equipment.

Signal loss can occur when metal, concrete, walls or floors block
transmission. Locate antennas in open areas or add APs as needed to
improve coverage.

In an open-air environment the radio range is up to 2000 ft. (606 m). In a
typical office or retail environment the radio range is between 180 and 250
ft (54.5 to 75.7 m).

Site Surveys

A site survey analyzes the installation environment and provides users with
recommendations for the equipment and its placement.

1.3 Advanced Radio Theory

To improve AP management and performance, users need to understand
basic AP functionality and configuration options. The AP includes features for
different interface connections and network management.

The AP provides MAC layer bridging between its interfaces. The AP monitors
traffic from its interfaces and, based on frame address, forwards the frames
to the proper destination. The AP tracks the frames sources and destinations
to provide intelligent bridging as MUs roam or network topologies change.
The AP also handles broadcast and multicast message initiations and
responds to MU association requests.

12 Spectrum24 Access Point AP-3020 Product Reference Guide

1.3.1 MAC Layer Bridging

The AP listens to all packets on all interfaces and builds an address database
using the unique IEEE 48-bit address (MAC address). An address in the
database includes the interface media that the device uses to associates with
the AP. The AP uses the database to forward packets from one interface to
another as they arrive. The bridge forwards packets addressed to unknown
systems to the Default Interface (either Ethernet or PPP). Users can use the
Ethernet interface as a wireless AP interface.

Users have up to four wireless AP interfaces available for the bridging
algorithm (v3.10 and above only).

Introduction

The AP internal stack interface handles all messages directed to the AP.

Spectrum24 Access Point AP-3020 Product Reference Guide 13

Introduction

Each AP stores information on destinations and their interfaces to facilitate
forwarding. When a user sends an ARP (Address Resolution Protocol) request
packet, the AP forwards it over all enabled interfaces (Ethernet, PPP, radio
and WLAP) except over the interface the ARP request packet was received.
On receiving the ARP response packet, the AP database keeps a record of
the destination address along with the receiving interface. With this
information, the AP forwards any directed packet to the correct destination.
The AP forwards packets for unknown destinations to the Ethernet interface.

Only ARP request packets received over radio are echoed-back over radio
for other APs to hear.

The AP removes from its database destinations or interfaces not used for a
specified time. The AP refreshes its database when it transmits or receives
data from these destinations and interfaces.

Filtering and Access Control

The AP provides facilities to limit the MUs that associate with it and the data
packets that can forward through it. Filters can provide network security or
improve performance by eliminating broadcast/multicast packets from the
radio network.

The ACL (Access Control List) contains the MAC addresses for MUs allowed
to associate with the AP. This provides security by preventing unauthorized
access.

The AP supports using a disallowed address list of destinations. This feature
prevents the AP from communicating with specified destinations. This can
include network devices that do not require communication with the AP or
its MUs.

14 Spectrum24 Access Point AP-3020 Product Reference Guide

Depending on the setting, the AP can keep a list of frame types that it
forwards or discards when they reach it. The Type Filtering option prevents
specific frames (indicated by the 16-bit DIX Ethernet Type field) from being
processed by the AP. These include certain broadcast frames from devices
unimportant to the wireless LAN but take up bandwidth. Filtering out
unnecessary frames can also improve performance.

1.3.2 Auto Fallback to Wireless Mode

The AP supports an Auto Fallback to Wireless when the hardware Ethernet
connection fails or becomes broken. The AP resets itself and during
initialization attempts to associate with any other WLAP in the network. This
feature is available only if the WLAP Mode is enabled and the Ethernet
Timeout parameter is set to one. See Configuring System Parameters on

page 39 and Wireless Operation Parameters on page 46.

1.3.3 DHCP Support

The AP uses Dynamic Host Configuration Protocol (DHCP) to obtain a leased
IP address and network configuration information from a remote server.
DHCP is based on BOOTP protocol. DHCP can coexist or interoperate with
BOOTP. An AP sends out a DHCP request searching for a DHCP server to
acquire the network configuration and firmware filenames. Because BOOTP
and DHCP are interoperable, whichever responds first becomes the server
allocating the information. The DHCP client automatically sends a DHCP
request every XX hours/days to renew the IP address lease as long as the AP
is running. (This parameter is programmed at the DHCP server. Example:
Windows NT servers typically are set for 3 days.) The AP can optionally
download two files when a boot takes place, the firmware file and an HTML
file, because firmware versions 4.00-31 and above support Web servers.
Users can program the DHCP or BOOTP server to transfer these two files
when a DHCP request is made.

Introduction

When the AP receives a network configuration change or not able to renew
the IP address lease the AP sends out an SNMP trap.

Spectrum24 Access Point AP-3020 Product Reference Guide 15

Introduction

1.3.4 Media Types

The AP supports bridging between Ethernet, radio and serial media.
The Ethernet interface fully complies with Ethernet Rev. 2 and IEEE 802.3

specifications. The AP supports 10Base-T wired connections and full-speed
filtering. The data transfer rate over radio waves is 1 or 2 Mbps. This rate
requires adjustment of AP application time-out values for data transfer
between the Ethernet and radio interfaces. The Ethernet interface is optional
for single-cell or PPP-connected networks.

The radio interface conforms to IEEE 802.11 specification. The interface
operates at 1 and 2 Mbps using frequency hopping, spread spectrum radio
technology. The AP supports multiple-cell operations with fast, transparent
roaming between cells. With the frequency-hopping system, each cell
operates independently. Each cell provides a 1 or 2 Mbps bandwidth. Adding
cells to the network provides increased coverage area and total system
capacity. The AP supports MUs operating in Power Save Polling (PSP) mode
or Continuously Aware Mode (CAM) without user intervention.

The DB-9, 9-pin, RS-232 serial port provides a UI (User Interface) or a PPP
(Point to Point Protocol) connection. The UI provides basic management tools
for the AP. The PPP provides a link between APs using a serial connection. The
serial link supports short haul (direct serial) or long haul (telephone-line)
connections. The AP is a DTE (Data Terminal Equipment) device with male
pin connectors for the RS-232 port. Connecting the AP to a PC requires a
null modem cable and connecting the AP to a modem requires a straight­through cable.

16 Spectrum24 Access Point AP-3020 Product Reference Guide

1.3.5 Bridging Support

The AP PPP (Point to Point Protocol) interface, accessible from the serial port
at the rear of the AP, provides two types of bridging operations:

• Data-link bridging between two APs. A network using a data-link bridge
provides radio coverage by using a remote AP in a location
geographically distant from the AP connected to the Ethernet network.
The remote AP cannot provide an Ethernet connection to other APs. MUs
associating with the remote AP transmit and receive from the Ethernet
network via the PPP link.

Introduction

Spectrum24 Access Point AP-3020 Product Reference Guide 17

Introduction

• Internet Protocol bridging between an AP and a computer. To establish
an Internet Protocol bridge with an AP, ensure the computer includes the
appropriate Telnet software with PPP and TCP/IP protocols. By using
Telnet, a computer at a remote location can connect to any AP on an
Ethernet network, as long as data transfers through IP packets.

A PPP link provides the option of using a direct serial link or modem to
extend wired Ethernet topologies.

Once in PPP mode, the AP automatically attempts to communicate with
the other device using the Data-Link Bridging (DLB) protocol. An AP using
DLB communicates on the MAC level, and receives and transmits
Ethernet frames.

If the other device does not support DLB, the AP attempts to communicate
using Internet Protocol Control Protocol (IPCP). An AP using IPCP
communicates on the IP level, and receives and transmits IP (Internet
Protocol) packets.

18 Spectrum24 Access Point AP-3020 Product Reference Guide

Introduction

The PPP implementation in the AP uses the Link Control Protocol (LCP) and
Network Control Protocol (NCP) as described in:

• RFC 1171: the Point-to-Point Protocol, July 1990

• RFC 1220: PPP Extensions for Bridging, April 1991

• RFC 1332: The PPP Internet Protocol Control Protocol, May 1992

• RFC 1661: The Point-to-Point Protocol, July 1994.

RFCs are Requests For Comments used in Internet Communities.

The AP database dynamically tracks MUs and APs on the PPP interface.
Packets forward to the PPP link after the AP determines their destination.

The PPP implementation in the AP uses the NCP as described in RFC 1220:
PPP Extensions for Bridging to encapsulate packets at the Ethernet level. The
PPP provides IP bridging control as defined by RFC 1172 and MAC-level
bridging. It provides support for PPP negotiations conforming to RFC 1661.
Users cannot plug a non-AP node directly into the AP serial port, only AP-to­AP PPP links.

Refer to RFC 1171: The Point to Point Protocol and RFC 1220: PPP Extensions
for Bridging for information.

Spectrum24 Access Point AP-3020 Product Reference Guide 19

Introduction

PPP Connection

Connecting two APs with a direct serial link requires a null-modem
serial cable.

Connecting two APs with modem devices requires straight-through cables
between the APs and modems. Using modems requires using a telephone
line for as long as the link remains active.

If using a modem connection, one AP represents the originating AP and the
other represents the answering AP. When using a PPP link, do not use the
serial port to access the UI. Access to the UI requires establishing a Telnet
session with the AP.

20 Spectrum24 Access Point AP-3020 Product Reference Guide

1.3.6 Frequency Hopping Spread Spectrum

The Spread spectrum technique (also known as broadband) takes a
narrowband signal and spreads the data signal over a broad segment of the
radio frequency band or spectrum. Spectrum24 uses the Frequency Hopping
Spread Spectrum (FHSS) technology for radio communication. FHSS spreads
the signal by transmitting a short burst on one frequency, jumping to another
frequency for another short burst and so on. Spectrum24 uses the 2.4 - 2.5
GHz range depending on the country, this range does not require licensing
from the FCC. FHSS offers a higher transmission rate than a conventional
radio narrowband method.

In FHSS systems, the carrier frequency of the transmitter changes (or hops) in
accordance with the pseudo-random code sequence. The code sequence
dictates the frequency order selected by the transmitter. The transmitter takes
the input data and spreads it in a predefined method. Each receiver has to
understand this predefined method and reconstruct the signal before
interpreting data. Stations in a cell using FHSS techniques hop or change the
carrier frequency at synchronized intervals. Government regulatory agencies
and standards, such as ETSI, MKK, the FCC and IEEE 802.11, determine the
number of frequency hops (79 for the U.S.), the hopping pattern (sequence
each frequency is used) and dwell time (time at each frequency). The FCC
requires 75 or more hopping frequencies used and a maximum of 400ms
for dwell time per frequency. The transmitter and receiver synchronize to the

Introduction

Spectrum24 Access Point AP-3020 Product Reference Guide 21

Introduction

hop sequence to ensure communication. The time synchronization field
included in message packets coordinates the hop timing of all units. The user
can program the length each hop lasts. Each hop is a frequency at least
6 MHz away from the previous frequency and has a 1 MHz bandwidth.

FHSS can survive in an adverse environment and coexist with other devices/
services in the same band. The average signal strength being relatively low
on any given frequency is a result of FHSS. When the signal intelligence is
spread out over several MHz in the frequency spectrum, the resulting power
spectrum also spreads out (less than 1 watt). This results in the transmitted
power spread out over a wide frequency bandwidth and makes detection
very difficult (without the code sequence).

Hopping provides enhanced data reception in the presence of interfering
signals, like fixed frequency radio networks or microwave ovens. The system
also resists interference because it spends a short time on each given
frequency. If an interfering source is present (interference at a specific
frequency), only a small number of frequency hops are blocked instead of
the entire range. With

interference occurring on one frequency, the data is

retransmitted on a subsequent hop at another frequency. Even if constant

22 Spectrum24 Access Point AP-3020 Product Reference Guide