TCP Candidates with Interactive Connectivity Establishment (ICE)
RFC 6544

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Internet Engineering Task Force (IETF)                      J. Rosenberg
Request for Comments: 6544                                   jdrosen.net
Category: Standards Track                                     A. Keranen
ISSN: 2070-1721                                                 Ericsson
                                                          B. B. Lowekamp
                                                                   Skype
                                                             A. B. Roach
                                                                 Tekelec
                                                              March 2012

    TCP Candidates with Interactive Connectivity Establishment (ICE)

Abstract

   Interactive Connectivity Establishment (ICE) defines a mechanism for
   NAT traversal for multimedia communication protocols based on the
   offer/answer model of session negotiation.  ICE works by providing a
   set of candidate transport addresses for each media stream, which are
   then validated with peer-to-peer connectivity checks based on Session
   Traversal Utilities for NAT (STUN).  ICE provides a general framework
   for describing candidates but only defines UDP-based media streams.
   This specification extends ICE to TCP-based media, including the
   ability to offer a mix of TCP and UDP-based candidates for a single
   stream.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6544.

Rosenberg, et al.            Standards Track                    [Page 1]
RFC 6544                         ICE TCP                      March 2012

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Rosenberg, et al.            Standards Track                    [Page 2]
RFC 6544                         ICE TCP                      March 2012

Table of Contents

   1. Introduction ....................................................4
   2. Terminology .....................................................5
   3. Overview of Operation ...........................................5
   4. Sending the Initial Offer .......................................7
      4.1. Gathering Candidates .......................................7
      4.2. Prioritization .............................................8
      4.3. Choosing Default Candidates ...............................10
      4.4. Lite Implementation Requirements ..........................10
      4.5. Encoding the SDP ..........................................11
   5. Candidate Collection Techniques ................................12
      5.1. Host Candidates ...........................................12
      5.2. Server Reflexive Candidates ...............................13
      5.3. NAT-Assisted Candidates ...................................13
      5.4. UDP-Tunneled Candidates ...................................14
      5.5. Relayed Candidates ........................................15
   6. Receiving the Initial Offer and Answer .........................15
      6.1. Considerations with Two Lite Agents .......................16
      6.2. Forming the Check Lists ...................................16