Stun - AudioCodes Mediant 1000 User Manual

SIP User's Manual
8.3.1

STUN

Simple Traversal of UDP through NATs (STUN), based on RFC 3489 is a client / server
protocol that solves most of the NAT traversal problems. The STUN server operates in the
public Internet and the STUN clients are embedded in end-devices (located behind NAT).
STUN is used both for the signaling and the media streams. STUN works with many
existing NAT types and does not require any special behavior.
STUN enables the device to discover the presence (and types) of NATs and firewalls
located between it and the public Internet. It provides the device with the capability to
determine the public IP address and port allocated to it by the NAT. This information is later
embedded in outgoing SIP / SDP messages and enables remote SIP user agents to reach
the device. It also discovers the binding lifetime of the NAT (the refresh rate necessary to
keep NAT 'Pinholes' open).
On startup, the device sends a STUN Binding Request. The information received in the
STUN Binding Response (IP address:port) is used for SIP signaling. This information is
updated every user-defined period (NATBindingDefaultTimeout).
At the beginning of each call and if STUN is required (i.e., not an internal NAT call), the
media ports of the call are mapped. The call is delayed until the STUN Binding Response
(that includes a global IP:port) for each media (RTP, RTCP and T.38) is received.
To enable STUN, perform the following:
Enable the STUN feature using either the Web interface (refer to ''Configuring the
Application Settings'' on page 71) or the ini file (set EnableSTUN to 1).
Define the STUN server address using one of the following methods:
•
Define the IP address of the primary and the secondary (optional) STUN servers
using either the Web interface (refer to ''Configuring the Application Settings'' on
page 71) or the ini file (STUNServerPrimaryIP and STUNServerSecondaryIP). If
the primary STUN server isn't available, the device attempts to communicate with
the secondary server.
•
Define the domain name of the STUN server using the ini file parameter
StunServerDomainName. The STUN client retrieves all STUN servers with an
SRV query to resolve this domain name to an IP address and port, sort the server
list, and use the servers according to the sorted list.
Use the ini file parameter NATBindingDefaultTimeout to define the default NAT
binding lifetime in seconds. STUN is used to refresh the binding information after this
time expires.
Notes:
Version 5.4
•
STUN only applies to UDP (doesn't support TCP and TLS).
•
STUN can't be used when the device is located behind a symmetric NAT.
•
Use either the STUN server IP address (STUNServerPrimaryIP) or
domain name (STUNServerDomainName) method, with priority to the
first one.
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8. Networking Capabilities
May 2008