A Media-Based Traceroute Function for the Session Initiation Protocol (SIP)
RFC 7403

Document Type RFC - Proposed Standard (November 2014; No errata)
Last updated 2015-10-14
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Internet Engineering Task Force (IETF)                         H. Kaplan
Request for Comments: 7403                                        Oracle
Category: Standards Track                                  November 2014
ISSN: 2070-1721

                   A Media-Based Traceroute Function
               for the Session Initiation Protocol (SIP)

Abstract

   SIP already provides the ability to perform hop-by-hop traceroute for
   SIP messages using the Max-Forwards header field to determine the
   reachability path of requests to a target.  A mechanism for media-
   loopback calls has also been defined separately, which enables test
   calls to be generated that result in media being looped back to the
   originator.  This document describes a means of performing hop-by-hop
   traceroute-style test calls using the media-loopback mechanism to
   test the media path when SIP sessions go through media-relaying back-
   to-back user agents (B2BUAs).

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/rfc7403.

Kaplan                       Standards Track                    [Page 1]
RFC 7403                Media Traceroute for SIP           November 2014

Copyright Notice

   Copyright (c) 2014 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................3
   3. The SIP Traceroute Mechanism ....................................4
      3.1. Processing a Received Max-Forwards Header Field ............4
      3.2. Answering the INVITE .......................................5
   4. Security Considerations .........................................5
   5. Normative References ............................................6
   Acknowledgments ....................................................7
   Author's Address....................................................7

1.  Introduction

   In many deployments, the media for SIP-created sessions does not flow
   directly from the originating User Agent Client (UAC) to the
   answering User Agent Server (UAS).  Often, SIP B2BUAs in the SIP
   signaling path also insert themselves in the media plane path by
   manipulating Session Description Protocol (SDP), either for injecting
   media such as rich ringtones or music-on-hold or for relaying media
   in order to provide functions such as transcoding, IPv4-IPv6
   conversion, NAT traversal, Secure Realtime Transport Protocol (SRTP)
   termination, media steering, etc.

   As more SIP domains get deployed and interconnected, the odds of a
   SIP session crossing such media-plane B2BUAs increases as well as the
   number of such B2BUAs any given SIP session may go through.  In other
   words, any given SIP session may cross any number of B2BUAs both in
   the SIP signaling plane as well as the media plane.

   When a failure or degradation occurs in the media plane, it is
   difficult to determine where in the media path it occurred.  In order
   to aid managing and troubleshooting SIP-based sessions and media

Kaplan                       Standards Track                    [Page 2]
RFC 7403                Media Traceroute for SIP           November 2014

   traversing such B2BUAs, it would be useful to progressively test the
   media path as it reaches successive B2BUAs with a test controlled
   solely by the source User Agent (UA).  A mechanism to perform media-
   loopback test sessions has been defined in [RFC6849], but it cannot
   be used directly to test B2BUAs because, typically, the B2BUAs do not
   have an Address of Record (AOR) to be targeted, nor is it known a
   priori which B2BUAs will be traversed for any given session.

   For example, suppose calls from Alice to Bob have media problems.
   Alice would like to test the media path to each B2BUA in the path to
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