Aastra 9143i Series Administrator's Manual page 247

RPORT
The Session Initiation Protocol (SIP) operates over UDP and TCP. When used
with UDP, responses to requests are returned to the source address from which the
request came, and returned to the port written into the topmost "Via" header of the
request. However, this behavior is not desirable when the client is behind a
Network Address Translation (NAT) or firewall.
A parameter created for the "Via" header called "Rport" in RFC 3581, allows a
client to request that the server send the response back to the source IP address
and the port from which the request came.
When you enable "Rport, the phone always uses symmetric signaling (listens on
the port used for sending requests).
An Administrator can configure "Rport" using the configuration files or the
Aastra Web UI.
Configuring Rport Using the Configuration Files
Use the following parameter to configure Rport on your phone.
sip rport
Configuration Files
For specific parameters you can set in the configuration files, see Appendix A, the section,
page A-31.
41-001160-03, Rev 00, Releaes 2.4
Configuring Network and Session Initiation Protocol (SIP) Features
Network Settings
"Rport Setting" on
4-65