STUN Description

STUN provides a mean for applications to discover the presence and type of firewalls or NATs between them and the public internet.

Additionally, in presence of a NAT STUN can be used by applications to learn the public Internet Protocol (IP) address assigned to the NAT.

For more information on STUN, check the following links :

• RFC 3489
• STUN on Wikipedia
• http://www.voip-info.org/wiki-STUN

Mobicents Sip Servlets STUN support

Mobicents Sip Servlets provides STUN support at the sip connector level through the STUN4J project available at https://stun4j.dev.java.net/ .

So each connector can choose whether or not it wants to use STUN to dicsover its public IP address and use this public IP address in SIP messages that will be sent through it.

To configure a SIP connector to be STUN enabled, you need to add the three following properties to the corresponding Connector tag in the server.xml (whether on jboss or Tomcat) :

useStun="true"
stunServerAddress="stun01.sipphone.com"
stunServerPort="3478"

• useStun : enable STUN for this connector
• stunServerAddress : The STUN server address that will be used for discovering the public IP address of this SIP connector
• stunServerPort : The STUN server port of the STUN server used in the previous property (will rarely be changed if ever)

Limitations and Future Work

STUN standard is currently being reworked in STUN-bis and STUN sits along side a number of other techniques to achieve NAT traversal.
These include TURN, ICE UPnP and Session Border controllers. ICE provides a framework pulls together a number of different techniques: STUN, TURN, RSIP, to allow a client to investigate its environment.

STUN-bis, TURN and ICE will be addressed in further versions of Mobicents Sip Servlets if current STUN support is really found too limited.