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Questions about using GPRS modem with PIC 16F877

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Advanced Member level 2
Jun 9, 2005
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I need to retrive some measures from remote location using GPRS modem & PIC16F877 and have some questions.
I am sorry I don't know much about the GPRS

1-is't possible to connect to the remote GPRS modem and send commands to the remote controller inorder to send back it's measurements?

2-Is it possible to make a wirless Websrver with the GPRS modem?

3-Is it possible to send and recive data within a GPRS connection between 2 GPRS modems

4-What's the benefite of using GPRS modem with TCP/IP or impleminting it on the micro compared with using only the GPRS link?

Hossam Alzomior

modem gprs attach

The implementation depend on the modem you will use. The GPRS modems are not all the same, some will have some extra (useful) features, some don't. I recommend you Telit GM862, any of GPRS or PCS version. It has built in TCP/IP stack.
1- It is possible. The easiest way is to initiate the data transfer from the modem side, to a remote location. But if you want to use the GPRS modem as a server (ready to accept incoming connections), you will have to keep the GPRS modem always attached to the GPRS context (thus having an IP address), and to listen to a certain port where you will expect incoming connections. The peer side will have to know the IP which was assigned to the modem in the moment of GPRS attach. Some GSM operators will allow you to have a fixed IP address, some don't, check this with your provider.
2 - It is, but you will have to write the HTTP protocol in the PIC (the telit have only TCP/IP) and manage the resources (documents, scripts, etc.). Again, you will have to use the method described at 1, attach to GPRS, then listen on port 80.
3 - If you use one side to initiate the TCP connection and the other side in listen mode, it is possible. Again, the initiator will have to know the IP of the peer fromn the moment of the GPRS attach.
4 - If you use a modem with built in TCP/IP stack, all the underlying protocols which forms PPP are transparent to you. The only thing you have to do is to manage the connection (set APN, userid, passw, dial socket, listen on port, etc). Otherwise, you will have to write all the protocols from the PPP stack (LCP, PAP, CHAP, IPCP, ...) and this is not easy. The only drawback in the case of modems with TCP/IP (for Telit at least) is that only one TCP (or UDP) socket can be active at one time. Otherwise, it's easy: set parameters, atach to gprs, dial socket (or listen on port), and when you have a connection, exchange data.



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gprs modem connection without tcp ip

GPRS operators often use RFC1918 reserved-for-lan ip addresses in which case internet hosts can't open a connection to a port on a GPRS device.

With such providers it may be possible to connect to a listening port from another gprs device on the same network.

gm862 gprs listen


1-How much dose Telit GM862 cost?and where to get it?

2-Is it possible to make GPRS connection without using the TCP/IP?

Hossam Alzomor

telit lcp

For Telit modems go to you will find some prices there.
GPRS connections are in almost all cases done with a peer in internet. I cannot imagine how would you do this without TCP/IP. TCP/IP is a must over GPRS, this is why almost all modem manufacturers have this stack built in.



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