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4-30 41-001343-02 REV04 – 05.2014
STUN is a protocol that allows the IP phones on a network to discover the presence and types of NATs and firewalls
between them and the public Internet. It also provides the ability for the phones to determine the public IP addresses
allocated to them by the NAT. STUN works with many existing NATs, and does not require any special behavior from
them. As a result, it allows the phones to work through existing NAT infrastructures.
TURN is a protocol that governs the reception of data over a connection by a single communications device operating
behind a NAT or firewall. A TURN server relays packets from an external IP address towards the IP phone only if that
phone has previously sent a packet through the same TURN server to that particular external IP address.
SIP NAT IP configurations takes precedence over the STUN/TURN configurations. Typically, the STUN/TURN configuration
is only used for media (RTP traffic) - not for signaling. (For signaling, you need to enable “Rport” if the NAT device does
not recognize SIP. For more information about “Rport”, see the section, “RPORT” on page4-52 of this release note.
The STUN/TURN configuration applies globally on the phone. If you configure both STUN and TURN on the phone, it dis-
covers what type of NAT device is between the phone and the public network. If the NAT device is full cone, restricted
cone, or port restricted cone, the phone uses STUN. If the NAT device is symmetric, the phone uses TURN.
If you configure STUN only, the phone uses STUN without the NAT discovery process.
If you configure NAT only, the phone uses NAT and does not perform the NAT discovery process during startup. TURN is
compatible with all types of NAT devices.
Limitations to Using STUN and TURN
• The Firewall type discovery process on the phone is limited to 20 seconds. If the discovery process fails, the STUN
server may not be configured correctly.
• When making a new phone call, the phone limits obtaining the port from the STUN/TURN server to 5 seconds. If the
call does not go through in 5 seconds, the phone makes the call using the Session Description Protocol (SDP) with a
local IP:port.
An Administrator can configure a STUN and/or TURN server on the IP Phones using the configuration files or the Aastra
Web UI.
Configuring STUN and TURN Servers Using the Configuration Files
Use the following parameters to configure STUN and TURN servers in your network.
• sip stun ip
• sip stun port
• sip turn ip
• sip turn port
• sip turn user
• sip turn pass
Note:
STUN does not work if the NAT device is symmetric.
Note:
The NAT IP configuration parameter takes precedence over the STUN and TURN parameters.
Configuration Files
For specific parameters you can set in the configuration files, see Appendix A, the sections:
• “SIP STUN Parameters” on pageA-27
• “SIP TURN Parameters” on pageA-28.