Re: PPP connection to a private APN

[Denis Kenzior <denkenz@gmail.com>]

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Hi Etienne,

 >
> Thank you for your help, I managed to obtain a dump of the ppp connection
> and I compared it with the ppp debug info from ofono.
>
> The modem negociates with the DCE for the correct DNS and IP addresses. But
> the modem receives a "CGEV: NW DEACT X25" message before obtaining the IP
> address. I checked the dump with wireshark, there is no exchange of username
> and password. Do you know if this is supposed to happen before or after
> obtention of the IP address ?

The way this is setup is slightly weird in GSM.  The PPP stack runs on 
the modem and it is supposed to ask for credential information and 
transparently forward it to the network during context activation.

 From your log it seems that the modem never asks for authentication 
information.  There could be several reasons for this, it might not 
support any authentication protocol, it might not support the auth 
protocol we support (CHAP + MD5), etc.  You will need to examine the 
wireshark results for why this happens.  But essentially the 
authentication phase is skipped.

>
> I am also wondering what are the possible causes of a "NW DEACT" ?

The network drops the GPRS connection.  Speculating here, but I suspect 
it is because the credentials are invalid ;)

>
> I tried with the same computer, sim card, APN, credentials, but another
> modem (Option GTM382, does not use the PPP module from ofono) and it
> connects fine.
>

I would try also with pppd and generate pppdump information.  If this 
succeeds then I would compare the two wireshark logs to figure out what 
goes wrong.  oFono supports the bare minimum of PPP that works on 99% of 
the hardware.  But honestly we never tried VPN style GPRS contexts, so 
it may be that we are missing something.

> Here is the log from ofono :
>
> ofonod[1911]: drivers/atmodem/network-registration.c:cops_cb() cops_cb:
> BOUYGTEL, 208 20 2
> ofonod[1911]: src/network.c:current_operator_callback() 0x82ea648, 0x82f0a68
> ofonod[1911]: Aux: < \r\n+CIEV: rssi,3\r\n\r\n+CIEV: service,1\r\n\r\n+CIEV:
> roam,0\r\n
> ofonod[1911]: drivers/atmodem/gprs-context.c:at_gprs_activate_primary() cid 1
> ofonod[1911]: Modem: > AT+CGDCONT=1,"IP","alstom-france-locomotive.fr"\r
> ofonod[1911]: Modem: < \r\nOK\r\n
> ofonod[1911]: drivers/atmodem/gprs-context.c:at_cgdcont_cb() ok 1
> ofonod[1911]: Modem: > AT+CGDATA="PPP",1\r
> ofonod[1911]: Modem: < \r\nCONNECT\r\n
> ofonod[1911]: drivers/atmodem/gprs-context.c:at_cgdata_cb() ok 1
> ofonod[1911]: drivers/atmodem/gprs-context.c:setup_ppp()
> ofonod[1911]: PPP: lcp: pppcp_generate_event: current state 0:INITIAL
> ofonod[1911]: PPP: event: 0 (Up), action: 2, new_state: 2 (CLOSED)
> ofonod[1911]: PPP: lcp: pppcp_generate_event: current state 2:CLOSED
> ofonod[1911]: PPP: event: 2 (Open), action: 1026, new_state: 6 (REQSENT)
> ofonod[1911]: PPP: lcp: pppcp_initialize_restart_count: current state 2:CLOSED
> ofonod[1911]: PPP: lcp: pppcp_send_configure_request: current state 2:CLOSED
> ofonod[1911]: PPP: gatchat/gatppp.c:ppp_enter_phase() 1

Just FYI: Here we enter PPP_PHASE_ESTABLISHMENT

> ofonod[1911]: PPP: lcp: pppcp_process_configure_request: current state 6:REQSENT
> ofonod[1911]: PPP: lcp: pppcp_generate_event: current state 6:REQSENT
> ofonod[1911]: PPP: event: 6 (RCR+), action: 2008, new_state: 8 (ACKSENT)
> ofonod[1911]: PPP: lcp: pppcp_send_configure_ack: current state 6:REQSENT
> ofonod[1911]: PPP: lcp: pppcp_process_configure_ack: current state 8:ACKSENT
> ofonod[1911]: PPP: lcp: pppcp_generate_event: current state 8:ACKSENT
> ofonod[1911]: PPP: event: 8 (RCA), action: 129, new_state: 9 (OPENED)
> ofonod[1911]: PPP: lcp: pppcp_initialize_restart_count: current state 8:ACKSENT
> ofonod[1911]: PPP: gatchat/gatppp.c:ppp_enter_phase() 3

Here we enter PPP_PHASE_NETWORK.  The PPP_PHASE_AUTHENTICATION is 
skipped because it was never negotiated in the ESTABLISHMENT phase.

Regards,
-Denis