The response further enables the STUN client to determine the type of NAT being used, since
different NAT types handle incoming UDP packets in different ways. STUN supports three of the
four main existing types of NAT: Full Cone, Restricted Cone and Port Restricted Cone. It does
not, however, support Symmetric NAT, also known as bidirectional NAT, although PHOENIX
STRATOS allows it to be detected and reports its presence to the user.
Once the client has discovered its public address, it can advise its peers of that address.
STUN is useful as a complement to protocols like SIP. SIP uses UDP packets to signal sound,
video and text traffic over the Internet, but does not enable communication to be established
when the devices at the ends of the communication circuit are behind NAT routings. This is why
STUN is customarily used in these applications, to permit communication to be established.
The connection with the STUN server is normally made through port 3478 by means of UDP.
The STUN server can then provide the client with an alternate IP and communication port.
For complete information on the STUN protocol, we recommend consulting:
http://tools.ietf.org/html/rfc3489
AEQ always has a PHOENIX unit available for test at “phoenixMaster@sip.aeq.es” URI
and its 2 SIP servers are also available at sip.aeq.es and sip2.aeq.es and with warranty
that both work according to the official standard.
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