Re: [lwip-users] PPPoS TCP Connection Reject

[Patrick Klos]

On 8/1/2018 11:00 AM, gzayzay wrote:
> Hello All-
>
> I am working with FreeRTOS + LWIP on a project using PPPoS. I have been able
> to successfully connect to the network and obtain an IP address after the
> PPP negotiation using a modem that we have on our embedded device.

If the PPP negotiation completes, then clearly the UART and serial line 
are working and passing data, and so is PPPoS.

> Once PPP negotiation completes, on our embedded device, I start my server
> application to listen for incoming connection on a particular port. Every
> time I attempt to connect to the server application from a client, I am
> getting a "Connection reject".

As far as the "Connection reject" on the TCP connection, you'll need to 
check your "accept" routine that handles the incoming new connection(s) 
- make sure it returns ERR_OK (or equivalent based on the API you're using).

> I can successfully ping the device and get a ping response. The interesting
> part is, whenever I set a breakpoint in the code where I except data/traffic
> to be taken out of the UART to be passed to the lwip stack for processing, I
> do not hit this breakpoint.

Workings pings gives further proof that the serial link is up and 
running properly.

> I have placed a logic analyzer on the UART line and I do not see data when a
> PPP session has been established. However, during the ppp negatation
> process, this path is the only way data gets to the LWIP stack and it is
> responding. My hypothesis is that the modem is receiving the traffic and
> processing it internally instead of passing it through to the UART so that
> the lwip stack can do the processing.

If you place a logic analyzer and don't see anything, I would guess 
you're not actually connecting the logic analyzer to either of the UART 
signals (or maybe the wrong UART?).

> In view of the above, is there an option in LWIP that needs to be set for
> PPP so that the modem passes data transparently? Are there some
> configuration for LWIP that I need to set?

PPPoS is logically a different module from LwIP.  The PPPoS module 
packetizes the serial stream, presenting the LwIP interface with 
packets.  There is no such thing as passing data transparently from the 
modem to LwIP.

Patrick Klos
Klos Technologies, Inc.