Stun - AudioCodes Mediant 1000 User Manual

SIP User's Manual
To solve these problems the following mechanisms are available:
STUN (refer to Section
First Incoming Packet Mechanism (refer to Section
RTP / T.38 No-Op packets according to the avt-rtp-noop draft (refer to Section
on page 304).
For SNMP NAT traversal, refer to Section

10.3.1 STUN

Simple Traversal of UDP through NATs (STUN) (according to 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
STUN enables the gateway to discover the presence (and types) of NATs and firewalls
located between it and the public Internet. It provides the gateway 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 gateway. It also discovers the binding lifetime of the NAT (the refresh rate necessary to
keep NAT 'Pinholes' open).
On startup the gateway 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 NATBindingDefaultTimeout.
At the beginning of each call, if STUN is needed (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:
Set the parameter 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 the parameters STUNServerPrimaryIP and STUNServerSecondaryIP. If the
primary STUN server isn't available, the gateway tries to communicate with the
secondary server.
•
Define the domain name of the STUN server using the StunServerDomainName
parameter. 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 parameter NATBindingDefaultTimeout to determine the default NAT binding
lifetime in seconds. STUN is used to refresh the binding information after this time
expires.
Notes:
Version 5.0
10.3.1
type
s, and does not require any special behavior from them.
•
STUN only applies to UDP (doesn't support TCP and TLS).
•
STUN can't be used when the gateway is located behind a symmetric
NAT.
•
For defining the STUN server, use either the STUNServerPrimaryIP or
STUNServerDomainName parameter, with priority to the first one.
below).
10.3.2
16.10 on page 388.
303
10. Networking Capabilities
on page 304)
10.3.3
December 2006