[asterisk-users] SIP via TCP - new TCP session per call or use same session for multiple calls?

Dovid Bender dovid at telecurve.com
Fri Dec 27 10:10:05 CST 2019

So long as the tcp socket is open your SBC should send the call back over
the same socket. Now it can be that your SBC is seeing the socket as
timing out. If you are using Kamailio you can have it send tcp keep alives
every so often so that the socket stays up.

On Fri, Dec 27, 2019 at 10:41 AM Benoit Panizzon <benoit.panizzon at imp.ch>

> Hi List
> I wonder how SIP via TCP is supposed to work. Not realy Asterisk
> related, but I hope you experts might be able to help out :-)
> One of our customers has a SIP device registering via a complex NAT. To
> benefit from TCP Connection Tracking, he choose TCP instead of UDP.
> So he expected, that an incoming call would be sent back to him on the
> already open TCP connection, making it easy to get through that NAT.
> This is not the case. Our SBC is attempting to initiate a new SIP TCP
> connection towards the NAT Firewall of the customer thus getting
> dropped because this is not the outgoing established connection opened
> during the registration.
> So, how should SIP via TCP work? Should one TCP session be used for all
> signaling of potentially multiple concurrent calls, as expected by our
> customer. Or is it usual to make one TCP session per call as observed?
> Mit freundlichen Grüssen
> -Benoît Panizzon-
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