Example 2

Another example is when a VoIP service is provided using symmetric-latching. A B2BUA/proxy sits between HNT endpoints and the Oracle Communications Session Border Controller, and calls do not appear to be behind NATs from the Oracle Communications Session Border Controller’s perspective. The Oracle Communications Session Border Controller’s primary role, other than securing softswitches and media gateways, is to provide symmetric latching so that HNT media will work from the endpoints.

To ensure the Oracle Communications Session Border Controller’s latching mechanism is restricted to the media from the endpoints when the SIP Via and Contact headers are the B2BUA/proxy addresses and not the endpoints’, the endpoint’s real (public) IP address in the SDP of the offer/answer is used. The B2BUA/proxy corrects the c= line of SDP to that of the endpoints’ public FW address.

The Oracle Communications Session Border Controller would then restrict the latching to the address in the SDP of the offer from the access realm (for inbound calls) or the SDP answer (for outbound calls).