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Interactive Connectivity Establishment (ICE) is a technique used incomputer networking to find ways for two computers to talk to each other as directly as possible inpeer-to-peer networking. This is most commonly used for interactive media such asVoice over Internet Protocol (VoIP),peer-to-peer communications, video, andinstant messaging. In such applications, communicating through a central server would be slow and expensive, but direct communication between client applications on theInternet is very tricky due tonetwork address translators (NATs),firewalls, and other network barriers.
ICE is developed by theInternet Engineering Task Force MMUSIC working group and is published as RFC 8445, as of August 2018,[1] and has obsolesced both RFC 5245[2] and RFC 4091.[3]
Network address translation (NAT) became an effective technique in delaying theexhaustion of the available address pool ofInternet Protocol version 4, which is inherently limited to around four billion unique addresses. NAT gateways track outbound requests from aprivate network and maintain the state of each established connection to later direct responses from the peer on the public network to the peer in the private network, which would otherwise not be directly addressable.
VoIP, peer-to-peer, and many other applications require address information of communicating peers within the data streams of the connection, rather than only in the Internet Protocol packet headers. For example, theSession Initiation Protocol (SIP) communicates theIP address of network clients for registration with a location service, so that telephone calls may be routed to registered clients. ICE provides a framework with which a communicating peer may discover and communicate its public IP address so that it can be reached by other peers.
Session Traversal Utilities for NAT (STUN) is a standardized protocol for such address discovery including NAT classification.Traversal Using Relays around NAT (TURN) places a third-party server to relay messages between two clients when direct media traffic between peers is not allowed by a firewall.