Avaya Nortel Communication Server 1000 Manual page 527

Confirm using natcheck
Run the natcheck program. Look for the message:
UDP loopback translation:
If this messages prints, then a two-way speech path should be available
between two IP Phones behind the NAT device. See
path" (page
Figure 106
Speech path
Confirm using IP Phone
Connect two IP Phones to the same NAT device and call from one phone to
the other. Confirm that a two-way speech path is achieved during the call.
Unidirectional packet flow
Confirm using natcheck
The natcheck tool cannot be used to determine if the private-to-public
mapping created by the NAT device is being kept alive by a unidirectional
packet flow.
Confirm using IP Phone
If an IP Phone behind a NAT device has a two-way speech path immediately
after being registered, and continues to have a two-way speech path 2
to 30 minutes later, then the NAT device address/port mapping is being
kept alive by the packets. If a one-way speech path occurs after this time
period, ensure that the IP Phone has the latest firmware version. If the IP
Phone has the latest firmware, then the problem lies with the NAT device.
Try replacing the NAT device with a different model.
If the one-way speech path problem is fixed after rebooting the IP Phone, it
is likely that the NAT device does not meet the requirement of unidirectional
packet flow. As well, ensure that the firmware on the IP Phone has the
latest firmware version (older firmware versions can be a possible source of
the one-way speech path problem).
Copyright © 2003–2008, Nortel Networks
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527).
Nortel Communication Server 1000
IP Line Fundamentals
NN43100-500 02.02 Standard
Release 5.5 4 February 2008
YES (GOOD for peer-to-peer)
Figure 106 "Speech
Requirements 527