[SR-Users] How to disable retransmits via TCP connection? etc.

[Vitaliy Aleksandrov]

Hi,
Don't want to sound like a captain obvious, but what I can say after a 
quick look at your traces is that both client and server are behind NAT 
and either some entity drops big packets silently or somebody drops ICMP 
(fragmentation needed) which doesn't allow TCP to adjust max MSS. The 
other strange thing is that you said that you set server's MTU to 800 
bytes, but server has sent a huge TCP segment with a total length of 
1548 bytes and "Don't fragment" bit set.

On 24/06/15 17:30, Andrey Utkin wrote:
> Thanks for all the suggestions.
> Have taken pcap dumps with commands
> tcpdump -i any -w /tmp/sip_tcp.pcap host <counterpart host>
>
> http://whdd.org/sip_tcp_server.pcap
> http://whdd.org/sip_tcp_client.pcap
>
> The only obviously bad thing I see is "[TCP Previous segment not
> captured]" mark on the packet client side dump which is the ending of
> INVITE request body.
> Googling on this message, I've found some advice at StackOverflow to
> tune TCP socket TCP_MAXSEG option.
>
>
> http://whdd.org/sip_tcp_mtu800_server.pcap
> http://whdd.org/sip_tcp_mtu800_client.pcap
>
> For this test I have set MTU to 800 on the server's only actual net
> interface, and restarted Kamailio. The situation stays the same,
> despite the packets show differently in wireshark.
> On client side, there's still "[TCP Previous segment not captured]",
> and on server side there's a mark "[TCP segment of a reassembled
> PDU]".
>
> Any review is greatly appreciated!
>