Snom 4S NAT Filter Admin Manual page 7

• Both http and https as web interface for simple access from
anywhere on the Internet.
• The filter supports Interactive Connectivity Establishment (ICE).
User agents that support this feature will optimize the media path
for the shortest possible delay.
• Media relay is established using connection-oriented media. User-
agents that are not NAT-aware inherently support this feature. This
makes the operation of the NAT filter backward compatible.
• User-Agents may self-refresh their bindings. With this feature,
bindings can be kept alive even when IP addresses are changed
dynamically and when the user agent is temporarily available from
the outside.
• Call-alive polling. During calls, the filter checks if the call is still
alive and terminates the call if this should not be the case. With this
feature, charging users for broken calls can be avoided.
•
Reliable and unreliable transport layers. The filter supports both
UDP and TCP transport layers. Full TLS support will be added soon.
• To- and From-Headers may be changed for calls. The filter talks to a
web application server to get this information.
• Simple request-routing feature. The web application server can
also change the request-URI. This makes simple routing possible,
which can be used e.g. for least cost routing.sually, the filter acts as
stateless proxy. That means, by default it just forwards the packets
and does not change the content of the attachments or the headers
themselves. That means, the filter will not interfere with applications
(instant messaging, presence, weather report, etc).
There are three exceptions to this rule:
• The first exception is a REGISTER request. When a user agent tries
to register and needs the support of the filter, the filter will set up
a local data structure representing the user agents. It will make
sure that the connection to the user agents stays alive. It will also
make sure that requests that are destined to the user agents will be
forwarded properly.
•
The second exception is a SDP attachment. The filter checks if the
user agent needs support (or must be recorded) and will in that case
add a local contact to the SDP that can be used for media relay.
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snom technology AG • 7