Cisco Cisco IOS Software Release 12.4(2)T

Before enabling the NAT Optimized SIP Media Path with SDP feature, be sure you understand the 
following concepts:

The media path can be shortened, decreasing voice delay.

More control of voice policy is possible because the media path is closer to the customer domain 
and not deep within the service provider cloud.

The NAT Optimized SIP Media Path with SDP feature provides the ability to optimize the media path 
taken by a SIP VoIP session when NAT is used. NAT forces the VoIP traffic to take at least one extra hop 
in the network, which usually results in several additional hops being added to the path between two IP 
hosts.

Cisco IOS NAT will add the relevant translation information per SIP session within the SIP protocol 
messages. The SIP Application Layer Gateway support within Cisco IOS NAT will extract this 
translation information from the SIP packets and create NAT table entries.

The “piggybacking” of NAT translation information within the SIP call flows, the design of how users 
interact with the application when they talk to it, will allow the media path of a SIP VoIP session between 
two calling parties to take the optimized routing path between each other.

This section contains the following procedures:

Perform this task to configure SDP messages with a NAT optimized SIP Media path including MD5 
authentication.