Structure-Aware Time Division Multiplexed (TDM) Circuit Emulation Service over Packet Switched Network (CESoPSN)
RFC 5086

Network Working Group                                 A. Vainshtein, Ed.
Request for Comments: 5086                                     I. Sasson
Category: Informational                                  Axerra Networks
                                                                 E. Metz
                                                                     KPN
                                                                T. Frost
                                                   Zarlink Semiconductor
                                                                 P. Pate
                                                       Overture Networks
                                                           December 2007

   Structure-Aware Time Division Multiplexed (TDM) Circuit Emulation
            Service over Packet Switched Network (CESoPSN)

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Abstract

   This document describes a method for encapsulating structured (NxDS0)
   Time Division Multiplexed (TDM) signals as pseudowires over packet-
   switching networks (PSNs).  In this regard, it complements similar
   work for structure-agnostic emulation of TDM bit-streams (see RFC
   4553).

Vainshtein, et al.           Informational                      [Page 1]
RFC 5086         TDM Circuit Emulation Service over PSN    December 2007

 Table of Contents

   1. Introduction ....................................................3
   2. Terminology and Reference Models ................................3
      2.1. Terminology ................................................3
      2.2. Reference Models ...........................................4
      2.3. Requirements and Design Constraint .........................4
   3. Emulated Services ...............................................5
   4. CESoPSN Encapsulation Layer .....................................6
      4.1. CESoPSN Packet Format ......................................6
      4.2. PSN and Multiplexing Layer Headers .........................8
      4.3. CESoPSN Control Word .......................................9
      4.4. Usage of the RTP Header ...................................11
   5. CESoPSN Payload Layer ..........................................12
      5.1. Common Payload Format Considerations ......................12
      5.2. Basic NxDS0 Services ......................................13
      5.3. Extending Basic NxDS0 Services with CE Application
           Signaling .................................................15
      5.4. Trunk-Specific NxDS0 Services with CAS ....................18
   6. CESoPSN Operation ..............................................20
      6.1. Common Considerations .....................................20
      6.2. IWF Operation .............................................20
           6.2.1. PSN-Bound Direction ................................20
           6.2.2. CE-Bound Direction .................................20
      6.3. CESoPSN Defects ...........................................23
      6.4. CESoPSN PW Performance Monitoring .........................24
   7. QoS Issues .....................................................25
   8. Congestion Control .............................................25
   9. Security Considerations ........................................27
   10. IANA Considerations ...........................................27
   11. Applicability Statement .......................................27
   12. Acknowledgements ..............................................29
   13. Normative References ..........................................30
   14. Informative References ........................................31
   Appendix A. A Common CE Application State Signaling Mechanism .....33
   Appendix B. Reference PE Architecture for Emulation of NxDS0
       Services ......................................................34
   Appendix C. Old Mode of CESoPSN Encapsulation Over L2TPV3 .........36

Vainshtein, et al.           Informational                      [Page 2]
RFC 5086         TDM Circuit Emulation Service over PSN    December 2007

1.  Introduction

   This document describes a method for encapsulating structured (NxDS0)
   Time Division Multiplexed (TDM) signals as pseudowires over packet-
   switching networks (PSN).  In this regard, it complements similar
   work for structure-agnostic emulation of TDM bit-streams [RFC4553].

   Emulation of NxDS0 circuits provides for saving PSN bandwidth, and
   supports DS0-level grooming and distributed cross-connect
   applications.  It also enhances resilience of CE devices to effects
   of loss of packets in the PSN.

   The CESoPSN solution presented in this document fits the Pseudowire