Interactive Connectivity Establishment

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Interactive Connectivity Establishment (ICE) is a technique used in computer networking involving network address translators (NATs) in Internet applications of Voice over Internet Protocol (VoIP), peer-to-peer communications, video, instant messaging and other interactive media. In such applications, NAT traversal is an important component to facilitate communications involving hosts on private network installations, often located behind firewalls.

ICE is developed by the Internet Engineering Task Force MMUSIC working group and is published as RFC 5245,[1] which has obsoleted RFC 4091.[2]


Since the number of IPv4 addresses is limited by their 32-bit representation, not every network-enabled device can have a unique public IPv4 address with which it would be visible on the Internet. Network Address Translators (NAT) work by changing a private address into a public one when an outbound request passes through them. When a client establishes TCP connections through SYN packets, the NAT updates an internal table with each entry creating a mapping between an internal, private IP address and a public one.[3] Many applications run into problems when put in this situation with one example being VoIP traffic where a client needs to register with a unique address to a Session Initiation Protocol (SIP) proxy. Another problem relates to firewalls which might block VoIP traffic completely. ICE provides a framework for dealing with these problems.

Session Traversal Utilities for NAT (STUN) is a client server protocol returning the public IP address to a client together with information from which the client can infer the type of NAT it sits behind while Traversal Using Relays around NAT (TURN) places a third party server to relay messages between two clients where peer to peer media traffic is not allowed by a firewall.

IETF Specifications[edit]

  • RFC 5389: Session Traversal Utilities for NAT (STUN).
  • RFC 5766: Traversal Using Relays around NAT (TURN): Relay Extensions to STUN.
  • RFC 5245: Interactive Connectivity Establishment (ICE): A Protocol for NAT Traversal for Offer/Answer Protocols.

See also[edit]


  1. ^ RFC 5245, Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal for Offer/Answer Protocols, J. Rosenberg (April 2010)
  2. ^ RFC 4091, The Alternative Network Address Types (ANAT) Semantics for the Session Description Protocol (SDP) Grouping Framework, G. Camarillo, J. Rosenberg (June 2005)
  3. ^ Müller A, Carl (2008) Behavior and Classification of NAT Devices and Implications for NAT Traversal, IEEE Network September/October 2008. [Accessed at: 2 April 2011]

External links[edit]