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Old 06-10-2010, 03:18 AM   #1
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PPP works with a modem and not with another one


Before starting with my problem : I sent the same message to the mgetty mailing list a few days ago, but this list do not seem to be active any more (no message at all on the list since I registered). If someone knows an appropriate place to send my question, I would appreciate the advice...
That said, let's go :

I have an embedded system with linux OS + PPP + mgetty, on which I establish a dialup link from a windows machine using pap authentification.
That worked well until I had to change MODEM model. I had a socket modem based on a connexan chipset, working well, and the new one is based on a silabs chipset.
Of course I tried different hardwares (modems and embedded mother board) to be sure it is not because of a faulty component.

Here is what I have done and noticed :

I activated mgetty and pppd log.

Without changing the init string, mgetty don't even call pppd :
06/07 09:33:52 yS0   match: user='PROTOCOL: V44', key='/AutoPPP/'
06/07 09:33:52 yS0   match: user='PROTOCOL: V44', key='*'*** hit!
06/07 09:33:52 yS0   calling login: cmd='/bin/login', argv[]='login PROTOCOL: V44'
It seems that mgetty catches a string reporting protocol from the modem, instead of '/AutoPPP/'.
So I found an AT command that disables protocol reporting (AT\V2). It works better, because mgetty catches user='/AutoPPP/' and calls pppd. but that is still not enough, pppd log show me that the LCP negociation fails :
sent [LCP ConfReq id=0x1 <asyncmap 0x0> <auth pap> <magic 0x7e8f3f7f> <pcomp> <accomp>]
rcvd [LCP ConfReq id=0x2 <asyncmap 0x0> <magic 0x1d547146> <pcomp> <accomp> <callback CBCP> <mrru 1614> <endpoint [local:47.4a.4f.8e.]>]
sent [LCP ConfRej id=0x2 <callback CBCP> <mrru 1614>]
sent [LCP ConfReq id=0x1 <asyncmap 0x0> <auth pap> <magic 0x7e8f3f7f> <pcomp> <accomp>]
sent [LCP ConfReq id=0x1 <asyncmap 0x0> <auth pap> <magic 0x7e8f3f7f> <pcomp> <accomp>]
rcvd [LCP ConfReq id=0x3 <asyncmap 0x0> <magic 0x1d547146> <pcomp> <accomp> <callback CBCP> <mrru 1614> <endpoint [local:47.4a.4f.8e.]>]
and it loops several times with LCP ConfReq and LCP ConfRej, until ending with :
LCP: timeout sending Config-Requests
Connection terminated.
So I spyed communications with wireshark on the windows machine : I can only see frames from windows to my embedded system, but it seems that no frames are comming back.

Any idea would be appreciated.

details :
OS version : linux 2.4.19
mgetty version : experimental test release 1.1.27-Oct21
modem : telecom design, model SMSIL, based on Si2493 chipset from silabs (

I can attach logs and config files (mgetty and pppd) if it helps.



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