Avaya Nortel Communication Server 1000 Manual page 121

Description
5
Depending on the length of time the call is muted and the duration of the NAT
translation aging timeout value, the NAT device might timeout 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 session timeout 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).
Hold
The Hold function differs from the Mute function as Hold does not
cause problems with the audio stream.
121)
Table 30
Hold process
Description
1
When an IP Phone user places a call on Hold, the audio stream in both the Transmit
(Tx) and Receive (Rx) directions closes.
2
The NAT device begins aging the translation.
When the audio stream is closed and no voice path is present, the IP Phone defaults to
sending periodic non-RTP packets to keep the NAT translation alive. Therefore, when
a call is put on Hold, the IP Phone defaults to sending these non-RTP packets.
3
When the call is retrieved from Hold, a new set of open audio-stream messages is
issued by the LTPS and new connections are established reusing the same NAT
translation.
NAT and VLAN
Support of Virtual LAN (VLAN) is entirely dependent on the Layer 2 switch
to which the IP Phone is immediately connected. Users behind a NAT router
may find that the configuration of a VLAN ID is unsupported by their NAT
router. See the documentation of the NAT router to determine if a VLAN
ID is supported.
Copyright © 2003–2008, Nortel Networks
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describes the Hold process.
Nortel Communication Server 1000
IP Line Fundamentals
NN43100-500 02.02 Standard
Release 5.5 4 February 2008
NAT Traversal feature 121
Table 30 "Hold process" (page