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RLP issues: connecting two GSM modems


April 2, 2014 - 2:54am, 2637 views

If somebody could give me a clue on this problem I’m facing, I will be very grateful.

I am facing unexpected problems while trying to connect two GSM modems (Cinterion MC55i).

To troubleshoot this I decided to test the modems with PCs (a PC-to-PC connection using the modems as interface).
And the results where:
- When the remote modem awnser the call and establish the connection, both DTEs are informed by the modems (and at the same time) with the message “connect 9600/RLP”
- I Only have a 60% (aprox) of successful data connection (and this is my problem … )
- The connection failure is always on the calling modem, because the RLP does not go up (and link to the GSM (and) the remote/called modem)
- The RLP on the “remote”/called modem goes always up, even in the case when the calling modem side didn’t managed to activate the RLP
- The calling modem hangs with the message “no carrier”
Main configuration settings:
S0:001 S3:013 S4:010 S5:008 S6:000 S7:060 S8:000 S10:070 S18:000
+CBST: 7,0,1
+CRLP: 61,61,78,6
+CR: 0
+CRC: 0
+IPR: 0
+COPS: 0,0,"P xxx" (I used “xxx” for obvious reasons)

If the full connection is fulfilled (RLP up on both sides) then it remains stable and I can transfer the amount of data that I want.
So far I decided to complaint to the GSM operator; the services in the contract are voice and data (3G)

Thanks in advance

PS: since a timming sequence of the events might help, here they are:
t0: dialing at the PCs Hyperterminal (ATD xxxx) and "enter"
t0+7sec. -> the remote modem awnser;
t0+22sec -> RLP established on both modems (if successful)
t0+298sec -> RLP goes up on the remote modem when the calling modem does not have RLP up, which is odd