ADTRAN AOS Version R10.1.0 Command Reference Manual page 1080

Command Reference Guide Global Configuration Mode Command Set
When the media anchoring device receives the SDP answer from the destination endpoint, the connection
information IP address and media description UDP port numbers will be replaced with the IP address of
the interface for which the SDP answer was originally destined (i.e. the interface on which the VoIP phone
is reachable) and a second port number within the media anchoring UDP port range. This will cause RTP
from the VoIP phone to be routed to the media anchoring device instead of the public network.
When the RTP session begins, packets inbound from the public network will have the far-end IP address
as the source and the media anchoring device as the destination. The anchoring implementation will
replace the source address with the IP address of the egress (to the IP phone) interface on the media
anchoring device, and it will replace the destination address with that of the VoIP phone. This information
is derived from the UDP port on which the packet was originally received from the network, because the
anchoring implementation stored this information when the port was allocated.
The same operation will occur on packets inbound from the IP phone. These packets will have the IP
phone's IP address and UDP port as the source and the media anchoring device as the destination. The
source IP address will be changed to that of the egress (to the public network) interface on the media
anchoring device, and the port will be changed to the anchoring port established when the SDP offer was
originally manipulated. The destination IP address and UDP port will be changed to that of the public
network endpoint.
60000CRG0-35E Copyright © 2012 ADTRAN, Inc. 1080