Ofono: adding support for the SIMCom A7605E-H

Ofono: adding support for the SIMCom A7605E-H

[Любимов Максим]

Hello Denis Kenzior

I'm working on adding SIMCom A7605E-H (A7602E-H) modem support to
ofono. By now, I have prepared a version of the modem driver that works
according to the manufacturer's recommendations. But there is a problem
related to the functioning of the PPP connection. After activating the
context in ofono, the PPP connection is established, and the /dev/ppp0
device appears on the system. But when I send a ping to an external
server, after a few replies (1-100), the replies from the server stop
coming.

The manufacturer provides instructions for the modem, which describes
the procedure for setting up a PPP connection through pppd. By
following this instruction, the connection is stable and ping responses
are not interrupted.

I checked if the previously sent commands to the modem from ofono
affect the stability of the connection. To do this, I launched ofono,
in which all the procedures for polling and configuring the modem were
carried out. The context in ofono was not active. Next, I started pppd
with a script written according to the manufacturer's recommendations,
so the context activation was performed using pppd from the place where
ofono would have done it. After that, the /dev/ppp0 device also
appeared in the system, but the ping responses from the server come
steadily. Therefore, we can conclude that the problem lies in the
implementation of the PPP protocol in ofono, which for some reason is
incompatible with the SIMCom A7605E-H modem.

How would you comment on this situation and in what direction would you
advise moving to solve this problem?

Best Regards,
Lyubimov Maxim

Re: Ofono: adding support for the SIMCom A7605E-H

[Любимов Максим]

Good afternoon! Thanks for your reply.

I followed your advice and got the PPP connection data log using the
g_at_ppp_set_recording function. The resulting file did not open in
wireshark. Subsequent analysis of the data showed that the file
contained URCs from the modem, which caused no responses from the
server, buffer overflows, and disconnection of the PPP connection.

I redirected the URC to a different port and everything works fine now.

Best Regards,
Lyubimov Maxim

Re: Ofono: adding support for the SIMCom A7605E-H

[Denis Kenzior]

Hi Максим,

On 6/22/23 04:24, Любимов Максим wrote:
> Hello Denis Kenzior
> 

Sorry for the late reply, was traveling last week.

> I'm working on adding SIMCom A7605E-H (A7602E-H) modem support to
> ofono. By now, I have prepared a version of the modem driver that works
> according to the manufacturer's recommendations. But there is a problem

Great!

> related to the functioning of the PPP connection. After activating the
> context in ofono, the PPP connection is established, and the /dev/ppp0

It is 2023, didn't think I'd hear the term 'PPP' again :)

> device appears on the system. But when I send a ping to an external
> server, after a few replies (1-100), the replies from the server stop
> coming.

So the IPCP is brought up successfully.  Sometimes these devices want DHCP to be 
run on the link or they assume there's nothing on the other side?

> 
> The manufacturer provides instructions for the modem, which describes
> the procedure for setting up a PPP connection through pppd. By
> following this instruction, the connection is stable and ping responses
> are not interrupted.

But hmm, you say pppd works just fine..

> 
> I checked if the previously sent commands to the modem from ofono
> affect the stability of the connection. To do this, I launched ofono,
> in which all the procedures for polling and configuring the modem were
> carried out. The context in ofono was not active. Next, I started pppd
> with a script written according to the manufacturer's recommendations,
> so the context activation was performed using pppd from the place where
> ofono would have done it. After that, the /dev/ppp0 device also
> appeared in the system, but the ping responses from the server come
> steadily. Therefore, we can conclude that the problem lies in the
> implementation of the PPP protocol in ofono, which for some reason is
> incompatible with the SIMCom A7605E-H modem.

You may want to post the pppd script, though I have honestly not used pppd in 
10+ years.

> 
> How would you comment on this situation and in what direction would you
> advise moving to solve this problem?

I would capture the pppd negotiation in PCAP and do the same with oFono (see 
g_at_ppp_set_recording()).  You can also try gatchat/gsmdial which performs most 
of the same basic steps as the atmodem gprs-context driver and can (optionally, 
with a command line argument) capture PCAPs  directly.

Then we can try and compare what might be different between the two.

Regards,
-Denis

Ofono: adding support for the SIMCom A7605E-H

[Любимов Максим]

Hello Denis Kenzior

I'm working on adding SIMCom A7605E-H (A7602E-H) modem support to
ofono. By now, I have prepared a version of the modem driver that works
according to the manufacturer's recommendations. But there is a problem
related to the functioning of the PPP connection. After activating the
context in ofono, the PPP connection is established, and the /dev/ppp0
device appears on the system. But when I send a ping to an external
server, after a few replies (1-100), the replies from the server stop
coming.

The manufacturer provides instructions for the modem, which describes
the procedure for setting up a PPP connection through pppd. By
following this instruction, the connection is stable and ping responses
are not interrupted.

I checked if the previously sent commands to the modem from ofono
affect the stability of the connection. To do this, I launched ofono,
in which all the procedures for polling and configuring the modem were
carried out. The context in ofono was not active. Next, I started pppd
with a script written according to the manufacturer's recommendations,
so the context activation was performed using pppd from the place where
ofono would have done it. After that, the /dev/ppp0 device also
appeared in the system, but the ping responses from the server come
steadily. Therefore, we can conclude that the problem lies in the
implementation of the PPP protocol in ofono, which for some reason is
incompatible with the SIMCom A7605E-H modem.

How would you comment on this situation and in what direction would you
advise moving to solve this problem?

Best Regards,
Lyubimov Maxim