Telit Wireless Solutions Easy GPRS User Manual

Easy GPRS User Guide

80000ST10028 Rev. 0 - 02/01/07

This document is relating to the following products:

Easy GPRS User Guide

80000ST10028 Rev. 0 - 02/01/07

GM862-GPS 3 990 250 657 GE863-GPS 3 990 250 660 GT863-PY 3 990 250 466

GM862-QUAD 3 990 250 655 GM862-QUAD-PY 3 990 250 656 GM862-QUAD 3 990 250 659 GM862-QUAD-PY 3 990 250 658

GE863-OUAD Pb balls 3 990 250 664

GE863-PY Pb balls 3 990 250 665

GE863-QUAD Pb free 3 990 250 653

GE863-PY Pb free 3 990 250 654

GE863-QUAD Pb free 3 990 250 662

GE863-PY Pb free 3 990 250 661

GE864-QUAD 3 990 250 675 GE864-PY 3 990 250 676

GE863-QUAD 3 990 250 651

GE863-PY 3 990 250 650

Easy GPRS User Guide

80000ST10028 Rev. 0 - 02/01/07

Contents

1 GPRS Operations ............................................................................................................................ 4

1.1 Introduction ............................................................................................................................................4

1.1.1 CSD application example ....................................................................................................................................6

1.1.2 GPRS application example..................................................................................................................................7

1.2 Preliminary GPRS context parameters setting....................................................................................8

1.2.1 Context parameter setting....................................................................................................................................8

1.2.2 Minimum Quality of the Service Requested........................................................................................................9

1.2.3 Requested Quality of the Service.......................................................................................................................11

1.3 GPRS context activation and data state entering..............................................................................13

1.4 GPRS data state exit.............................................................................................................................15

2 Enhanced Easy GPRS Extension ................................................................................................. 16

2.1 Overview................................................................................................................................................16

2.1.1 Easy GPRS Outgoing connection.................................................................................................. ....................17

2.1.1.1 Configuring the GPRS access...................................................................................................................17

2.1.1.2 Configuring the embedded TCP/IP stack..................................................................................................17

2.1.1.3 Saving settings for the Internet peer to be contacted.................................................................................17

2.1.1.4 Request the GPRS context to be activated................................................................................................18

2.1.1.5 Open the connection with the internet host...............................................................................................18

2.1.1.6 Close the Socket without deactivating the context....................................................................................18

2.1.2 Easy GPRS Incoming Connection.....................................................................................................................19

2.1.2.1 Defining the Internet Peer that can contact this device (firewall settings)................................................19

2.1.2.2 Request the socket connection to be opened in listen ...............................................................................20

2.1.2.3 Receiving connection requests..................................................................................................................20

2.1.3 FTP Client..........................................................................................................................................................21

2.1.4 Email Client.......................................................................................................................................................21

2.1.5 Known limitations..............................................................................................................................................21

2.2 FTP OPERATIONS.............................................................................................................................22

2.2.1 Opening and Closing an FTP Connection..........................................................................................................22

2.2.2 Setting the FTP Transfer Type...........................................................................................................................23

2.2.3 FTP File transfer to the server ...........................................................................................................................23

2.2.4 FTP File download from the server...................................................................................................................24

2.3 Examples ...............................................................................................................................................26

2.3.1 Easy GPRS - HTTP client application ...............................................................................................................26

2.3.2 Easy GPRS - EMAIL sending application......................................................................................................... 28

2.3.3 Easy GPRS -EMAIL receiving application....................................................................................................... 30

2.3.4 Remote connection between two modules.........................................................................................................32

3 List of acronyms............................................................................................................................. 34

4 Document Change Log.................................................................................................................. 35

Easy GPRS User Guide

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1 GPRS Operations

1.1 Introduction

The General Packet Radio Services (GPRS) standard permits DATA transfers in a completely different way with respect to previous point to point communications made with Circuit Switch Data (CSD) GSM modems. In CSD operations the modem establishes a connection with the other party (another modem) in such a way that all the Network devices in between are transparent to the data exchanged, simulating a real point to point connection, just as if the other party is directly connected with the controlling application of the modem. The other party can be either an Internet Service Provider (ISP) or a private server, but in any case, the arrival point must have a modem to connect to (Landline, ISDN or GSM CSD). The connection establishment procedure defines a particular path where all the information exchanged

Easy GPRS User Guide

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In GPRS operations instead, the connection is made directly towards internet as if the GPRS modem was a network IP socket interface. There's no data path reserved for the data exchange between the two peers, instead the resources are allocated dynamically on demand and the data exchanged is organized into packets typically TCP/IP, furthermore the maximum transfer speed can be much faster than GSM CSD. An example of GPRS connection is shown in the following picture, where the GPRS connection is between the GPRS modem and the internet as if all the devices inside the dashed line are not present:

GPRS interconnectivity

Due to this kind of connection, when activating the GPRS connection you must provide the network parameters to enter through the internet point of the GPRS network ISP (Internet Service Provider) and not the phone number to be dialed; therefore it is not possible to establish a direct point to point GPRS connection between two modems as in CSD case, instead an internet tunneling must be done to achieve a point to point connection between two peers. This approach as the immediate advantage of projecting the controlling application of the GPRS modem directly on the internet, ready to be accessed virtually from anywhere in the world at the same cost on the GPRS; actually the billing of the GPRS connection is based on the amount of data exchanged (number of packets transferred) independently from the time the connection is active or where these packet must be delivered. Therefore, it is possible to leave the controlling application always connected and ready to receive/send data on demand, while paying only for the data really exchanged. The drawback of the GPRS connection is that the controlling application must have its own TCP/IP protocol stack embedded to decode the packets that arrive from GPRS and encode the ones to be sent through the internet. There are few considerations than must be done on the GPRS connections:

• the GPRS connection speed with a GPRS class 10 multislot device is asymmetrical, 3 time slots in reception (43200 bps max) and 2 time slot in sending (28800 bps max) or 4 time slots in reception (57600 bps max) and 1 time slot in sending (14400 bps max).

• The controlling application of the module must have a TCP/IP - PPP software stack to interface with the GPRS modems.

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• The controlling application must relay on some ISP that may be the Network Operator of the SIM to gain access to the internet through the GPRS connection.

• Because of the point before, the receiving application must have internet access either.

• Since the communication is based upon TCP/IP packets, then it is possible to talk

contemporarily with more than one peer.

• When required, the data security in internet shall be guaranteed by security protocols over the TCP/IP that must be managed by the controlling application.

A modem can be in 4 different states:

• GPRS DETACHED, which corresponds to the "not reachable" condition for the GPRS service;

• GPRS ATTACHED, which corresponds roughly to the "registered" condition for the GPRS service;

• GPRS context activated, which corresponds to the “reachable on the network” condition with IP address assigned (this is possible with AT command: AT#GPRS=1 and also some other AT commands)

• CONNECTED, which roughly corresponds to the connected status;

A thing that must be noted on the GPRS connect, is the fact that, if the mobile IP address (the internet address) is assigned by the ISP dynamically, then when the GPRS context of the device is not activated it has no address and therefore it cannot be reached by internet requests. The same thing occurs in the case the GPRS device has a static IP address assigned to it by the ISP, but it is DETACHED. In these cases there's no possibility for the internet peer to "call" the GPRS device through internet, the only way to alert it is to call it in GSM mode (either a Data or a Voice call are suited) and the GPRS module application must recognize the caller, eventually abort the GSM call and connect to the internet in GPRS to receive the packets from the internet peer.

NOTE: Mobile device can be reachable from internet network only if the IP assigned by the operator is public IP; not all operators offer this service.

To explain further the differences between CSD and GPRS an example application made in both ways will be shown.

1.1.1 CSD application example

Let’s suppose you have several remote meteorological measurement units spread around the territory, and you want to access them wirelessly through a GSM module in CSD operation. For each remote unit, there's a modem to connect with the server application, with its own SIM card and unique phone number. Now there are two possibilities:

• the server application calls on demand the remote units, provided it has stored their phone numbers in a private database.

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• the remote units call the server application modem when needed and eventually retry in the case they found it busy; this time the phone number to be stored is only one, the server number which must be stored on the remote units.

In both cases, once connected, the remote unit sends the meteorological data to the server, which places it in a central database for further reading by anyone who accesses the meteorological internet site for example. The drawback of this approach is that the CSD modem needs about 30s to establish the connection and, depending on the amount of data to be transferred (usually few hundreds bytes), some seconds to transfer them. So let’s say we pay a 40s call while we need only 10s to transfer data.

1.1.2 GPRS application example

The same application can be preformed with all the Telit modules using the GPRS feature. The remote unit is always connected to the internet taking advance of the features of the GPRS system, when it needs to send data to the server application it simply fills the TCP/IP packets for the server with the meteorological data and gives them to the Telit module to deliver. The central server has a single modem to connect to the internet, receives the TCP/IP packets from all the remote units and places the contained data in the central database. The advantage of using GPRS is that the remote unit is always connected and reachable and it pays only for the amount of data (small) transferred and not for the connection time as in CSD operations; in addiction the call billing is equal for devices placed anywhere in the Network Operator State and the server can be anywhere in the World. Furthermore, in the CSD operation the server shall have a set of modems and multiple phone lines to ensure that the calling units will not find it busy, while a single modem is enough for GPRS operation. The speed at which the packets can be downloaded is up to 57600 bps (class 10 device working at 4+1), 4 times faster than CSD.

In the following paragraphs more detailed information will be given on how to establish GPRS connection.

Easy GPRS User Guide

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1.2 Preliminary GPRS context parameters setting

1.2.1 Context parameter setting

The context parameters are all the set of information to identify the internet entry point interface provided by the ISP. With these parameters the GPRS network identifies the ISP to be used to gain access to the internet and defines the value of the IP address of the GPRS device once connected.

• send command

AT+CGDCONT[=[<cid>[,<PDP_type>[,<APN>[,<PDP_addr>[,<d_comp>[,<h_comp>[,<pd 1>[,…[,pdN]]]]]]]]]]<cr>

where: <cid> - (PDP Context Identifier) numeric parameter which specifies a particular PDP context

definition.

1..max - where the value of max is returned by the Test command <PDP_type> - (Packet Data Protocol type) a string parameter which specifies the type of packet data

protocol "IP" - Internet Protocol "PPP" - Point to Point Protocol <APN> - (Access Point Name) a string parameter that represents logical name used to select GGSN

or external packet data network. If the value is null or omitted, then the subscription value will be requested.

<PDP_addr> - a string parameter that identifies the terminal in the address space applicable to the

PDP. The allocated address may be read using the +CGPADDR command. <d_comp> - numeric parameter that controls PDP data compression 0 - off (default if value is omitted) 1 - on <h_comp> - numeric parameter that controls PDP header compression 0 - off (default if value is omitted) 1 - on

<pd1>, …, <pdN> - zero to N string parameters whose meanings are specific to the <PDP_type> NOTE: a special form of the Set command, +CGDCONT=<cid>, causes the values for context

number <cid> to become undefined. NOTE: issuing AT+CGDCONT<CR> is the same as issuing the Read command. NOTE: issuing AT+CGDCONT=<CR> returns the OK result code.

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• wait for response:

Response Reason Action

OK context parameters have been

successfully stored

ERROR some error occurred check parameters and retry

For example:

1- Let's assume you want to set-up the GPRS context number 1(cid) with your GPRS connection parameters APN: ibox.tim.it IP address: dynamically assigned by the ISP Packet Data Protocol type: Internet Protocol (IP) Data compression: OFF Header compression: OFF

command:

AT+CGDCONT= 1,"IP","ibox.tim.it","0.0.0.0",0,0 <cr>

response

proceed ahead

1.2.2 Minimum Quality of the Service Requested

The minimum quality of service requested parameters represent the boundary under which the connection quality is not anymore acceptable and will be terminated.

• send command

AT+CGQMIN=<cid>,<precedence>,<delay>,<reliability>,<peak>,<mean><cr>

where:

<cid> - is the index number of the desired context to be written (up to 5 different context). <precedence> - is the precedence class. It is applied when the network has a heavy duty and user

precedence must be followed to ensure operations, the higher the priority the better the service. 0 - subscribed (default) 1 - High priority 2 - Normal priority 3 - Low priority

<delay> - is the delay class. It represents the maximum allowable time delay class between the sending and the reception of a packet.

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0 - subscribed (default) 1 - delay class 1 2 - delay class 2 3 - delay class 3 4 - delay class 4 (best effort)

<reliability> - is the connection reliability class. It represents the connection reliability requested, the higher is the number the less reliable is the data exchanged. 0 - subscribed (default) 1 - reliability class 1 (acknowledged GTP,LLC and RLC; protected data) 2 - reliability class 2 (unacknowledged GTP, acknowledged LLC and RLC; protected data) 3 - reliability class 3 (unacknowledged GTP and LLC, acknowledged RLC; protected data) 4 - reliability class 4 (unacknowledged GTP,LLC and RLC; protected data) 5 - reliability class 5 (unacknowledged GTP,LLC and RLC; unprotected data)

<peak> - is the peak data transfer throughput

0 - subscribed (default) 1 - up to 7,8 kbps 2 - up to 15,6 kbps 3 - up to 31,3 kbps 4 - up to 62,5 kbps 5 - up to 125 kbps 6 - up to 250 kbps 7 - up to 500 kbps 8 - up to 1000 kbps 9 - up to 2000 kbps

<mean> - is the mean data transfer throughput

0 - subscribed (default) 1 - up to 0,8 kbps 2 - up to 1,6 kbps 3 - up to 3,9 kbps 4 - up to 7,8 kbps 5 - up to 15,6 kbps 6 - up to 39 kbps 7 - up to 78 kbps 8 - up to 156 kbps 9 - up to 390 kbps 10 - up to 7,6 Mbps 11 - up to 15.2 Mbps 12 - up to 38.2 Mbps 13 - up to 76.3 Mbps 14 - up to 152 Mbps 15 - up to 381 Mbps 16 - up to 762 Mbps 17 - up to 1525 Mbps 18 - up to 3815 Mbps

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31 - Best Effort

• wait for response:

Response Reason Action

OK context parameters have been

successfully stored

ERROR some error occurred check parameters and retry.

NOTE: If your minimum requirements are too high, then it can happen that it is impossible to establish a GPRS connection, because the network has not enough resources to guarantee that quality of service. If does this happen, then you shall try reducing your minimum quality requirements.

For example: 1- Let's assume you want to set-up the GPRS context number 1(cid) written before with your GPRS

min QoS parameters: Precedence class: Normal priority Delay class: subscribed Reliability class: subscribed Peak throughput: not less than 15,6 kbps Mean throughput: not less than 7,8 kbps

command:

AT+CGQMIN= 1,2,0,0,5,4 <cr>

response

NOTE: Telit suggests to setup AT+CGQMIN=1,0,0,0,0,0

proceed ahead

1.2.3 Requested Quality of the Service

The requested quality of service parameters represents the connection quality that is requested to the network on GPRS context activation.

• send command

AT+CGQREQ=<cid>,<precedence>,<delay>,<reliability>,<peak>,<mean><cr>

where: <cid> - is the index number of the desired context to be written (up to 5 different context).

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