Overview; Applications - Snom 4S NAT Filter Admin Manual

1
The snom 4S NAT Filter enables non-NAT aware devices to
operate in private networks. The filter operates typically on a public IP
address. Non-NAT aware devices are automatically refreshed; NAT-aware
devices that operate behind symmetrical NAT may self-refresh their
bindings using the built-in STUN server of the filter. Devices on public
Internet traverse the filter without changes or refreshes. By supporting
Interactive Communications Establishment (ICE), the number of calls that
must go through the filter can be minimized.
The operator version of the product also offers recording
capabilities. Through a separate management interface, operators
can define numbers that are silently recorded. The filter records in
uncompressed PCAP format which is primary important for troubleshooting
and signalling recording. It also offers a compressed mode where only the
voice part of the conversation is recorded in highly-compressed audio
format (13.2 kBit/s).
The operation of the filter is similar to a session border controller.
However, we do not like the term "session border", because the filter
does not control sessions nor is it on the border of a call. It does also not
translate signalling, e.g. from SIP to H.323 or to MGCP. If all user agents
are fully NAT-compliant or on public Internet, the filter can transparently
be removed from the network without changing of the call flows or
functionality. Also, the filter does not interfere with unknown applications.
This is tremendous advantage against session borders controllers which
need software update for new applications.

1.1 Applications

The filter can be used in the following scenarios:
• Corporations. Corporations which operate their infrastructure be-
hind NAT and/or firewalls can talk to the public Internet through the
filter.
• Operators. Operators offer the NAT traversal feature to their cus-

Overview

snom technology AG • 5