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Tunneling Multiplexed Compressed RTP (TCRTP)
RFC 4170

Document type: RFC - Best Current Practice (November 2005; No errata)
Also Known As BCP 110
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

IETF State: (None)
Consensus: Unknown
Document shepherd: No shepherd assigned

IESG State: RFC 4170 (Best Current Practice)
Responsible AD: Allison Mankin
Send notices to: <csp@csperkins.org>, <magnus.westerlund@ericsson.com>

Network Working Group                                        B. Thompson
Request for Comments: 4170                                      T. Koren
BCP: 110                                                         D. Wing
Category: Best Current Practice                            Cisco Systems
                                                           November 2005

             Tunneling Multiplexed Compressed RTP (TCRTP)

Status of This Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document describes a method to improve the bandwidth utilization
   of RTP streams over network paths that carry multiple Real-time
   Transport Protocol (RTP) streams in parallel between two endpoints,
   as in voice trunking.  The method combines standard protocols that
   provide compression, multiplexing, and tunneling over a network path
   for the purpose of reducing the bandwidth used when multiple RTP
   streams are carried over that path.

Thompson, et al.         Best Current Practice                  [Page 1]
RFC 4170          Tunneling Multiplexed Compressed RTP     November 2005

Table of Contents

   1. Introduction ....................................................3
      1.1. Is Bandwidth Costly? .......................................3
      1.2. Overview of Protocols ......................................3
      1.3. Document Focus .............................................4
      1.4. Choice of Enhanced CRTP ....................................4
      1.5. Reducing TCRTP Overhead ....................................4
   2. Protocol Operation and Recommended Extensions ...................4
      2.1. Models .....................................................5
      2.2. Header Compression: ECRTP ..................................5
           2.2.1. Synchronizing ECRTP States ..........................5
           2.2.2. Out-of-Order Packets ................................6
      2.3. Multiplexing: PPP Multiplexing .............................6
           2.3.1. PPP Multiplex Transmitter Modifications for
                  Tunneling ...........................................7
           2.3.2. Tunneling Inefficiencies ............................8
      2.4. Tunneling: L2TP ............................................8
           2.4.1. Tunneling and DiffServ ..............................9
      2.5. Encapsulation Formats ......................................9
   3. Bandwidth Efficiency ...........................................10
      3.1. Multiplexing Gains ........................................10
      3.2. Packet Loss Rate ..........................................10
      3.3. Bandwidth Calculation for Voice and Video Applications ....10
           3.3.1. Voice Bandwidth Calculation Example ................12
           3.3.2. Voice Bandwidth Comparison Table ...................13
           3.3.3. Video Bandwidth Calculation Example ................13
           3.3.4. TCRTP over ATM .....................................14
           3.3.5. TCRTP over Non-ATM Networks ........................14
   4. Example Implementation of TCRTP ................................15
      4.1. Suggested PPP and L2TP Negotiation for TCRTP ..............17
      4.2. PPP Negotiation TCRTP .....................................17
           4.2.1. LCP Negotiation ....................................17
           4.2.2. IPCP Negotiation ...................................18
      4.3. L2TP Negotiation ..........................................19
           4.3.1. Tunnel Establishment ...............................19
           4.3.2. Session Establishment ..............................19
           4.3.3. Tunnel Tear Down ...................................20
   5. Security Considerations ........................................20
   6. Acknowledgements ...............................................21
   7. References .....................................................21
      7.1. Normative References ......................................21
      7.2. Informative References ....................................22

Thompson, et al.         Best Current Practice                  [Page 2]
RFC 4170          Tunneling Multiplexed Compressed RTP     November 2005

1.  Introduction

   This document describes a way to combine existing protocols for
   compression, multiplexing, and tunneling to save bandwidth for some
   RTP applications.

1.1.  Is Bandwidth Costly?

   On certain links, such as customer access links, the cost of

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