[Serusers] [Serdev] Strange behaviour in SER

[Martin Hoffmann]

Nuno Ribeiro wrote:
> 
> I would like your opinion about a scenario, i.e. if the SER is having the
> correct behavior in our scenario. The scenario is the following one:
> We have a basic scenario where a SIP proxy sends an INVITE and afterwards a
> CANCEL message to another SIP proxy. The last SIP Proxy answers with a 513
> Message too big to the CANCEL message. When the first proxy receives this
> answer message it will discard it and won't forward it back to the client
> that tried to establish a call. In attachment I send you  the wireshark
> capture.

CANCELs are hop-by-hop, meaning that proxies process the CANCEL instead
of forwarding it. While the process it and if necessary, they create a
new CANCEL for the request they sent on earlier.

You can see that in your trace. When the proxy (10.112.64.80, port 5060)
receives the CANCEL in message 12, it creates a 200 OK for it and sends
it back in message 14 and also creates a new CANCEL in message 13 which
it sends on. When it then receives the 513 in message 14, the first
CANCEL has already been answered and it can't do a thing.

HTH and regards,
Martin