User's Manual

Features Page 165 of 910
IP Line Description, Installation and Maintenance
4 The NAT device sees that the IP Phone’s UDP connection is not active in the
transmit direction and starts aging the translation
.
5 Depending on the length of time the call is muted and the duration of the NAT’s
translation aging timeout value, the NAT device might time-out the translation and
drop the connection
.
6 All packets coming from the far end are dropped by the NAT device.
7 When mute is cancelled, the IP Phone starts transmitting again.
8 NAT considers this to be a new connection and creates a new translation. NAT
sends data to the far end using this new translation, resulting in half-duplex voice
connection between the IP Phone and the far-end device
.
9 Data sent to the far end device gets there but the data coming back is lost.
Solution
1 The IP Phone periodically sends an extra non-RTP packet to the far end to keep
the NAT translation alive
, ensuring that the NAT’s session time-out does not
expire.
2 The non-RTP packet is constructed to fail any RTP validation tests so it is not
played out by the far-end device (IP Phone or gateway channel
.
Table 26
Mute process (Part 2 of 2)
Description