ACCESS Product Manual
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Network Address Translation (NAT) refers to the ability of a router to
translate requests from computers (or codecs) within its LAN onto the
public Internet. On its most basic level, this involves replacing the private
“source” or return IP address in each packet with the true public IP and
remembering where that packet was sent so that any response can be
forwarded back to the proper device. A good metaphor for this would
be that an outgoing packet punches a hole in the router, through which
authorized reply packets may be returned to the codec for a limited time,
as shown in Figure 38.
The Traversal Server aids in breaking through these different types of
routers for incoming calls. Because it is in constant contact with all
subscribed codecs, it can send and receive test patterns to determine
whether one or more NAT routers exist on a link and what type they are.
It can then choose a connection method to be used to circumvent the
problem. Options available to it include:
• Instructing the calling codec to make a normal connection (No
NAT detected).
• Using the hole punched by connection to the Directory Server
for incoming connections from other codecs.
• Instructing the called codec to make the connection in the
reverse direction.
Figure 38 - “Punching a Hole” in a NAT Router
