How do I configure the SBC to reuse the TCP connection created for incoming for outgoing?

The following mechanisms will allow the SBC to use an already created inbound TCP/TLS connection for outbound requests:

 

1.) The presence of the "alias" parameter in a Via header, as explained in draft-ietf-sip-connect-reuse-08.

 

2.) The other end of the connection is behind a NAT. When the SBC sees that the Via sent-by does not match the source address of the connection it will automatically reuse the connection to deliver requests to the UA.

 

3.) The Contact address of a REGISTER request received on a TCP connection matches the source address and port. This is because the contact address is the ephemeral port the UA used to form the connection to the SBC and therefore will not be listening on that port for inbound connections.