Snom 4S manual Scaling and Redundancy, Nat

2.

[ S N O M 4 S N A T F I L T E R ]

a=rtpmap:0 pcmu/8000 a=rtpmap:8 pcma/8000 a=rtpmap:3 gsm/8000 a=rtpmap:18 g729/8000 a=rtpmap:2 g726-32/8000 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-15

a=sendrecv a=silenceSupp:off - - - -

The NAT Filter changes the private address to a globally routable address and inserts the local port. It also inserts a hint that tells the other user agent that it should not do silence suppression. This reduces the risk that the connection is closed during a talk spurt of one of the parties.

2.4 Scaling and Redundancy

The NAT Filter product was designed to support distributed server farms. That means that the servers act stateless in principle; user agents may randomly pick a server in a server farm. This feature allows opera- tors to set up very large and robust networks.

Table 1: NAT conbimations

To/From	Public IP	Full Cone	Restricted	Symmetrical
		NAT	NAT	NAT
Public IP	Always	When	When STUN	When STUN
		STUN	and ICE are	and ICE are
		support is	available	available
		available
Full Cone NAT		When	When STUN	When STUN
		STUN is	and ICE are	and ICE are
		available	available	available
Restricted			When STUN	When STUN
NAT			and ICE are	and ICE are
			available	available
				and no port
				checking
Symmetrical				Needs filter
NAT

18 • Architecture