Page 160 of 910 Features
553-3001-365 Standard 4.00 August 2005
Supported Cone NAT routers include:
• Full Cone
• Restricted Cone
• Port Restricted Cone
Note: A Cone NAT router with more than one IP Phone connected to it
must support hairpinning. Hairpinning occurs when an IP Phone behind
a NAT router can send packets to the Public IP address and port of
another IP Phone connected to the same NAT router.

Echo Servers

NAT Traversal is a function of the CS 1000 Release 4.5 software, and not a
function of the NAT router. NAT Traversal uses two Echo Servers residing
on the Signaling Server. Echo Server 1 detects the presence of a NAT router,
while Echo Server 2 detects the type of NAT router. Both Echo Server 1 and
Echo Server 2 are required for the NAT Traversal feature to function
properly.
If a compatible NAT router is detected, successful IP Phone registration
occurs and the software invokes the NAT Mapping Keep Alive function to
prevent loss of the IP connection. If an incompatible NAT is detected, an error
is displayed on the IP Phone’s display and the IP Phone is not allowed to
register.

Mapping

When an IP Phone is used in a private network behind a NAT device, the
NAT router strips the IP Phone’s private IP address and private port number
and assigns it a public IP address and public port number.
IMPORTANT!
Symmetric NAT routers are not supported. If the IP Phone is behind a
Symmetric NAT, IP Phone registration is unsuccessful and the IP Phone
displays a “NAT Error! ITG3053” message.