How to use the SIP NAT Traversal Controller API

The SIP NAT Traversal Controller API provides interfaces to the SIP stack to perform the following tasks:

• To retrieve the address-port pairs allocated by NAT, use the CSIPNATTraversalController::ResolvePublicAddrL and MSIPNATTraversalRequestObserver::PublicAddrResolved function.

• To start sending regular keepalive messages after receiving the 200 OK response for REGISTER request, use CSIPNATTraversalController::RefreshNATBindingL.

  Note: It is assumed that NAT Traversal Controller plug-in sends the keepalive messages in regular intervals after SIP stack calls this method.

The SIP stack and NAT Traversal Controller plug-in share a socket for sending messages over UDP or TCP. It uses the same source IP address and UDP/TCP port for sending SIP and UNSAF protocol messages over UDP or TCP. SIP stack manages the shared socket when you use the following interfaces:

• The SIP stack notifies NAT Traversal Controller plug-in when the next move for NAT binding keepalives changes by calling CSIPNATTraversalController::UpdateNextHop.

• If the SIP stack receives data from the shared socket that it does not identify, it passes the data to the external NAT Traversal Controller plug-in when you call CSIPNATTraversalController::DataReceivedL.

• Before the SIP stack releases the resources used by the NAT Traversal Controller plug-in, the SIP stack calls CSIPNATTraversalController::FreeResources.

• Synchronize the control to the shared socket to prevent NAT Traversal Controller plug-in and SIP stack that try to send the data using the same socket at the same time. SIP stack can allow or deny the NAT Traversal Controller plug-in permission to use the shared socket by calling CSIPNATTraversalController::SocketIdle.