[SIP Beyond VoIP] STUN keep-alive

[Andreas Sikkema]

Mihai

> I am having some problems with starting an audio call between two clients if
> they registered at some time one from another(aprox. 1 minute). I used ngrep
> to see sip traffic and this is what I saw: if clients register at aprox. the
> same time(less then a minute apart) if one of them sends the INVITE message
> the other client receives it, however if they’ve registered at some time one
> from another, the first client to have registered does not receive the
> INVITE.

Are these clients behind the same NAT router? I have seen lots of
consumer/prosumer grade NAT implementations that can't handle two SIP
clients on LAN side using the same local port (say 5060) when talking
to the same server on the WAN side. The last one to talk to the server
will receive all the traffic from the server, regardless of which was
the intended receipient. Moving one of the clients to a different
local port from which to send the messages resolves this. There is
nothing the server can do, the problem is on the LAN side of the NAT
router.

-- 
Andreas Sikkema