snom technology AG • 7
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S N O M
4 S N A T F
I L T E R
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Both http and https as web interface for simple access from
anywhere on the Internet.
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The filter supports Interactive Connectivity Establishment (ICE).
User agents that support this feature will optimize the media path
for the shortest possible delay.
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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.
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User agents may self-refresh their bindings. With this feature, bind-
ings can be kept alive even when IP addresses are changed dy-
namically and when the user agent is temporarily available from the
outside.
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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.
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Reliable and unreliable transport layers. The filter supports both
UDP and TCP transport layers. Full TLS support will be added soon.
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To and From headers may be changed for calls. The filter talks to a
web application server to get this information.
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Simple request-routing feature. The web application server can also
change the request-URI. This makes simple routing possible, which
can be used for least cost routing, for example. Usually, 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:
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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 destined to the user agents will be forwarded
properly.
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The second exception is an 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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