Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols
This document describes a protocol for Network Address Translator
(NAT) traversal for UDP-based multimedia sessions established with
the offer/answer model. This protocol is called Interactive
Connectivity Establishment (ICE). ICE makes use of the Session
Traversal Utilities for NAT (STUN) protocol and its extension,
Traversal Using Relay NAT (TURN). ICE can be used by any protocol
utilizing the offer/answer model, such as the Session Initiation
Protocol (SIP).
Session Traversal Utilities for NAT (STUN)
Session Traversal Utilities for NAT (STUN) is a protocol that serves
Session Traversal Utilities for NAT (STUN) is a protocol that serves
as a tool for other protocols in dealing with Network Address
Translator (NAT) traversal. It can be used by an endpoint to
determine the IP address and port allocated to it by a NAT. It can
also be used to check connectivity between two endpoints, and as a
keep-alive protocol to maintain NAT bindings. STUN works with many
existing NATs, and does not require any special behavior from them.
STUN is not a NAT traversal solution by itself. Rather, it is a tool
to be used in the context of a NAT traversal solution. This is an
important change from the previous version of this specification (RFC
3489), which presented STUN as a complete solution.
Traversal Using Relays around NAT (TURN): Relay Extensions to Session Traversal Utilities for NAT (STUN)
If a host is located behind a NAT, then in certain situations it can
be impossible for that host to communicate directly with other hosts
(peers). In these situations, it is necessary for the host to use
the services of an intermediate node that acts as a communication
relay. This specification defines a protocol, called TURN (Traversal
Using Relays around NAT), that allows the host to control the
operation of the relay and to exchange packets with its peers using
the relay. TURN differs from some other relay control protocols in
that it allows a client to communicate with multiple peers using a
single relay address.
The TURN protocol was designed to be used as part of the ICE
(Interactive Connectivity Establishment) approach to NAT traversal,
though it also can be used without ICE.