Symmetric NAT Traversal

The Symmetric NAT Traversal feature allows the passage of VoIP packets between endpoints when one (but not both) of the endpoints resides on a private network behind a NAT (Network Address Translation) device. This allows the IMG 2020 to check the media source of incoming Realtime Transport Protocol (RTP) packets, and allows the endpoint to advertise its presence inside or outside of Network Address Translation (NAT). Using this enables symmetric NAT traversal by supporting the capability to modify and update an existing RTP session remote address and port. When Symmetric NAT Traversal is enabled, the IMG 2020 will look for incoming packets from the distant end and use the source address information in those packets to define the IP address and UDP port information that must be sent back out via RTP to the distant end. The Comedia feature is based on the Comedia IETF draft version 04 (draft-ietf-mmusic-sdp-comedia).

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