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Re: request of help with GPRS & ppp on ETRAX-LX box

> jo wrote:
> Hello to everybody
> Probably this is a navie question but I'm not expert on PPP protocols
> (LCP IPCP and so on)
> I was setting up the ppp package for etrax-lx just as a black-box
> allowing to spuervise remote PLC
> from a control center as far as it will speak ppp over a GPRS movil
> modem.
> This is the main frame and I was able to buld the ppp package but I
> cann't link the GPRS network
> and the log of that comunication was:
> ....
> stuff for dialing
>  -- got it
> send (\\d\\c\\n^M)
> timeout set to 120 seconds
> Serial connection established.
> using channel 27
> Using interface ppp0
> Connect: ppp0 <--> /dev/ttyS0
> sent [LCP ConfReq id=0x1 <asyncmap 0x0> <pcomp> <accomp>]
> rcvd [LCP ConfAck id=0x1 <asyncmap 0x0> <pcomp> <accomp>]
> rcvd [LCP ConfReq id=0x1 <mru 1500> <asyncmap 0x0> <pcomp> <accomp>
> <auth
> pap>]
> sent [LCP ConfRej id=0x1 <auth pap>]

At this point your pppd rejects the PAP authentication, which was

> rcvd [LCP ConfReq id=0x2 <mru 1500> <asyncmap 0x0> <pcomp> <accomp>]
> sent [LCP ConfAck id=0x2 <mru 1500> <asyncmap 0x0> <pcomp> <accomp>]

But that does not matter, because the GPRS modem sends another ConfReq
option PAP. And this is Ack'ed by the ppp deamon.
PPP protocol says, that at this point, when both partners of the PPP
link have sent an ConfAck for LCP, the LCP protocol layer has
been established. So everything ok so far ...

> sent [LCP EchoReq id=0x0 magic=0x0]
> sent [IPCP ConfReq id=0x1 <addr> <ms-dns1> <ms-dns3
> rcvd [LCP TermReq id=0x3]

The GRPS modem does not like one of the options in the IPCP ConfReq i
(option "ms-dns3" is suspect).  PPP protocol specification says
that in this case the GPRS shall send an ConfRej for the option.
But my experience with GPRS modems has shown, that they behave only
at LCP layer in accordance with the PPP protocol specification. Instead
doing correct ConfRejects for IPCP protocol, they send a simple LCP
without giving an indicator for the possible error.

> LCP terminated by peer
> sent [LCP TermAck id=0x3]
> rcvd [LCP EchoRep id=0x0 magic=0x0]
> Connection terminated.
> [root@AxisProduct /mnt/flash/etc/ppp]374#

This is a correct PPP link termination.

Another possible source of error: First you do an GPRS attach, then
the ppp protocol, this takes one or two seconds. Perhaps your network
has decided to throw you out of his GRPS network. In this case you would
the TermReq as shown above (PPP protocol specification says that each
can send a TermReq at any time, even during negotiation).

Norbert Matzke                                                #
Geo++ GmbH, Steinriede 8, D-30827 Garbsen, Germany            ###
phone +49-(0)5131-4689-0, fax +49-(0)5131-4689-99             #####
email mailto:norbert.matzke@xxxxxxx.de, web http://www.geopp.de #######