Snom 4S manual Requirements on User Agents, Non NAT-Aware User Agents, STUN/ICE-Aware User Agents

2.

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

The snom 4S NAT Filter includes a STUN server that operates on the SIP UDP port. User agents should send their test packets to the SIP port.

2.6 Requirements on User Agents

Generally, there are two categories of user agents: The non NAT aware user agents and the STUN/ICE capable user agents.

2.6.1 Non NAT-Aware User Agents

Non-NAT aware user agents must have at least the following fea-

tures:

1.Must send SIP UDP packets from the port where they receive SIP traffic

2.Must start sending media immediately after receiving SDP

Requirement 1 is not fulfilled by the default configuration of the Cisco 7960; however there is a setting that enables this feature. Most known user agents support this feature, however.

Requirement 2 sometimes creates problems with user agents who don’t send media during silent periods. In this case, users have to start speaking before two-way audio can be established.

In any case, customers are asked to contact their vendor in case of problems and explanations. In general, snom recommends using NAT- aware user agents to reduce the network and support overhead.

2.6.2 STUN/ICE-Aware User Agents

STUN/ICE-Aware User Agents must implement the two IETF stan- dards. It is ok if the user agents use the built-in STUN server for refresh- ing the bindings and learning the public IP address.

snom phones starting with version 2.05a fall into this category.

20 • Architecture