Media5 Mediatrix 4104, Reference Manual

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Mediatrix 4104 285
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STUN Configuration
This chapter describes how to configure the STUN client of the Mediatrix 4104.
What is STUN?
STUN (Simple Traversal of UDP through NATs) is a simple client / server protocol that uses UDP packets to
discover the configuration information of NATs and firewalls between a device and the public Internet:

NAT type

NAT binding public address

NAT binding time to live
NAT (Network Address Translator) is a device that translates the IP address used within a “private” network
to a different IP address known in another “public” network. See
“NAT Traversal” on page 262 for more
details.
STUN supports a variety of existing NAT devices and does not require any additional hardware or software
upgrades on the NAT device.
The Mediatrix 4104 uses the STUN protocol to discover its NAT binding for the following three IP addresses/
ports (sockets):

Signalling protocol (SIP) IP address/port

RTP IP address/port

T.38 IP address/port
SIP Outbound Proxy
For a unit to work properly behind a firewall, it must keep a pinhole opened by sending keepalive packets
through the firewall.
The Mediatrix 4104 only sends keepalive packets to the last destination for a specific socket. When a unit is
not configured with an outbound proxy, it can send, through its SIP socket, messages to various destinations,
such as a SIP redirect server, another SIP unit, or a MWI server. If, for instance, the last SIP message was
sent to the MWI server, the Mediatrix 4104 will keep the pinhole opened for the MWI server only (sending
keepalive message to the MWI server) and won't be reacheable by other units outside the firewall.
To avoid those issues, all SIP message should come and go from the same source/destination on the public
side of the firewall, i.e., a SIP outbound proxy. Media5 thus recommends that you use a SIP outbound proxy.
See
“Outbound Proxy Server” on page 166 for more details.
Restrictions on the Media5 STUN Implementation

The Mediatrix 4104 does not currently support NAT type discovery.

The Mediatrix 4104 does not currently support STUN NAT binding time to live discovery.

The Mediatrix 4104 does not currently support the TLS security mechanism.

Due to a limitation of most routers, an RTP portal might be required in order for two units behind
the same NAT/firewall to be able to communicate with each other.
Standards Supported RFC 3489 – STUN - Simple Traversal of User Datagram Protocol (UDP)
Through Network Address Translators (NATs)