[En-Nut-Discussion] unreliable tcp

[Moritz Struebe]

Hi Szemző (however you pronounce that :-) )

I'm not familiar with the Ethernut (I'm here because of Nut/OS), but I 
have a bit of experience with networks. A good thing to do with strange 
network stuff us to take an old hub (you can still get them at Ebay) and 
then start sniffing using a second device (PC). This way you even get 
the Ethernet frames. (I once had a DSL-Modem which was a bit peculiar 
about talking to different routers/network cards).

Cheers
Morty

Szemző András schrieb:
> Hi guys,
>  
> Sorry for the long email...
>  
> I have an embedded linux based tcp receiver, which runs a small tcp server
> app. I have 2 clients connected to it. One is avr based and use GPRS,
> another AT91SAM7X based and use ethernet.(both use ethernut) If the
> at91sam7x and the server is both on local net, there are no problems.
>  
> The interesting things happens, when the server is on an adsl line. Not
> every adsl, just some of them has this "feature". 
> My app sends alive messages in every 1min, and get answer from the server.
> Both are a 16byte packet.
> Normally for 10 or 20 mins everything runs ok, but randomly the at91sam7x
> based client reconnect to the server, while the GPRS
> client is on the server since 2 days. 
>  
> I tried to use Commview to capture packets, and I see the sam7x doesn't get
> answer within a time. Normally it sends a PUSH ACK, get answer PUSH ACK,
> and send ACK. I see when there are problems, it tries to send PUSH ACK with
> retransmission, and if it gets answer it doesn't reconnect.
> My app's loop send a packet if it needs, than read back the answer, and with
> 100ms RECV timeout tries to read to see, if he got some incoming packets.
> I see when there are reconnects, the NutTcpReceive() will return with -1,
> wich means socket is disconnected. (sock->so_state will be 0 in this case)
>  
> I tried to increase the send and receive timeout to 5000ms, but it doesn't
> helped much. 
>  
> The interesting is I have a virtual modul running on linux, and if that is
> connected once, it will be online 2 or 3 days, until you shut it down.
> So I thing the problem is not server app related, just network, or adsl
> related. Maybe linux's tcp stack can handle better this cases. 
>  
> I see retransmitted packets, so it's not that retransmit bug just checked in
> the cvs. ( anyway I applied that, without help)
>  
> Have you got an idea what can I debug, or increase retransmit count from 7
> to some bigger? (I'll make some pictures about the packets with Commview)
>  
>  
> Thanks, 
> Andras
>  
>
> ----
> Kometa 99 Élelmiszeripari ZRt.
> Székhely: 7400 Kaposvár, Pécsi u. 67-69., Levelezési cím: 7401 Kaposvár, Pf. 58
> Cégszám: Somogy Megyei Bíróság mint Cégbíróság 14-10-300239
> Adószám: 13749619-2-44
> Telefon: 82/502-400, Fax: 82/502-415
> http://www.kometa.hu
> http://www.kemencessult.hu
>
> _______________________________________________
> http://lists.egnite.de/mailman/listinfo/en-nut-discussion
>
>