





Network Working Group                                           N. Jones
Request for Comments: 3255                                 Agere Systems
Category: Standards Track                                      C. Murton
                                                         Nortel Networks
                                                              April 2002


    Extending Point-to-Point Protocol (PPP) over Synchronous Optical
     NETwork/Synchronous Digital Hierarchy (SONET/SDH) with virtual
            concatenation, high order and low order payloads

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This document describes an extension to the mapping of Point-to-Point
   Protocol (PPP) into Synchronous Optical NETwork/Synchronous Digital
   Hierarchy (SONET/SDH) to include the use of SONET/SDH SPE/VC virtual
   concatenation and the use of both high order and low order payloads.

Table of Contents

   1.  Introduction................................................1
   2.  Rate Comparisons............................................2
   3.  Physical Layer Requirements.................................4
   4.  Standards Status............................................5
   5.  Security Considerations.....................................5
   6.  References..................................................6
   7.  Acknowledgements............................................6
   8.  Authors' Addresses..........................................7
   9.  Full Copyright Statement....................................8

1. Introduction

   Current implementations of PPP over SONET/SDH are required to select
   transport structures from the relatively limited number of
   contiguously concatenated signals that are available.




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   The only currently supported SONET/SDH SPE/VCs in RFC 2615 [3] are
   the following:

          SONET                   SDH
      ----------------------------------------
      STS-3c-SPE                  VC-4
      STS-12c-SPE                 VC-4-4c
      STS-48c-SPE                 VC-4-16c
      STS-192c-SPE                VC-4-64c

   Note that VC-4-4c and above are not widely supported in SDH networks
   at present.

   The use of virtual concatenation means that the right size SONET/SDH
   bandwidth can be selected for PPP links.

   For the convenience of the reader, the equivalent terms are listed
   below:

          SONET                   SDH
      ---------------------------------------------
      SPE                         VC
      VT (1.5/2/6)                Low order VC (VC-11/12/2)
      STS SPE                     Higher Order VC (VC-3/4/4-Nc)
      STS-1 frame                 STM-0 frame (rarely used)
      STS-1 SPE                   VC-3
      STS-1-nv                    VC-3-nv (virtual concatenation)
      STS-1 payload               C-3
      STS-3c frame                STM-1 frame, AU-4
      STS-3c SPE                  VC-4
      STS-3c-nv                   VC-4-nv (virtual concatenation)
      STS-3c payload              C-4
      STS-12c/48c/192c frame      STM-4/16/64 frame, AU-4-4c/16c/64c
      STS-12c/48c/192c-SPE        VC-4-4c/16c/64c
      STS-12c/48c/192c payload    C-4-4c/16c/64c

   This table is an extended version of the equivalent table in RFC 2615
   [3].  Additional information on the above terms can be found in
   Bellcore GR-253-CORE [4], ANSI T1.105 [5], ANSI T1.105.02 [6] and
   ITU-T G.707 [7].

2. Rate Comparisons

   Currently supported WAN bandwidth links for PPP over SONET/SDH:







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         ANSI                   ETSI
      -----------------------------------------------------
        STS-3c (150Mbit/s)     STM-1 (150Mbit/s)
        STS-12c (620Mbit/s)    STM-4 AU-4-4c (620Mbit/s)
        STS-48c (2.4Gbit/s)    STM-16 AU-4-16c (2.4Gbit/s)
        STS-192c (9.6Gbit/s)   STM-64 AU-4-64c (9.6Gbit/s)

   Note that AU-4-4c and AU-4-16c are not generally available in SDH
   networks at present.

   With virtual concatenation the following additional WAN bandwidth
   links would be available for PPP over SONET/SDH:

        SONET

      VT-1.5-nv (n=1-64)       1.6Mbit/s-102Mbit/s
      STS-1-nv  (n=1-64)       49Mbit/s-3.1Gbit/s
      STS-3c-nv (n=1-64)       150Mbit/s-10Gbit/s

        SDH

      VC-12-nv (n=1-64)        2.2Mbit/s-139Mbit/s
      VC-3-nv  (n=1-64)        49Mbit/s-3.1Gbit/s
      VC-4-nv  (n=1-64)        150Mbit/s-10Gbit/s

   Higher levels of virtual concatenation are possible, but not
   necessarily useful.  Lower levels of virtual concatenation are
   defined in the telecommunications standards for use if needed.

   Table 1 and Table 2, respectively depict the SONET/SDH transport
   structures that are currently available to carry various popular bit
   rates.  Each table contains three columns.  The first column shows
   the bit rates of the service to be transported.

   The next column contains two values:

   a) the logical signals that are currently available to provide such
   transport and, b) in parenthesis, the percent efficiency of the given
   transport signal without the use of virtual concatenation.

   Likewise, the final column also contains two values:

   a) the logical signals that are currently available to provide such
   transport and, b) in parenthesis, the percent efficiency of the given
   transport signal with the use of virtual concatenation.






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   Note, that Table 1, contains SONET transport signals with the
   following effective payload capacity: VT-1.5 SPE = 1.600 Mbit/s,
   STS-1 SPE = 49.536 Mbit/s, STS-3c SPE = 149.760 Mbit/s, STS-12c SPE =
   599.040 Mbit/s, STS-48c SPE = 2,396.160 Mbit/s, and STS-192c SPE =
   9,584.640 Mbit/s.

         Table 1. SONET Virtual Concatenation

       Bit rate     Without            With
      --------------------------------------------

       10Mbit/s    STS-1 (20%)   VT-1.5-7v (89%)
       100Mbit/s   STS-3c (67%)  STS-1-2v (100%)
       200Mbit/s   STS-12c(33%)  STS-1-4v (100%)
       1Gbit/s     STS-48c(42%)  STS-3c-7v (95%)

   Similarly, Table 2, contains SDH transport signals with the following
   effective payload capacity: VC-12 = 2.176 Mbit/s, VC-3 = 48.960
   Mbit/s, VC-4 = 149.760 Mbit/s, VC-4-4c = 599.040 Mbit/s, VC-4-16c =
   2,396.160 Mbit/s, and VC-4-64c = 9,584.640 Mbit/s.

         Table 2. SDH Virtual Concatenation

       Bit rate     Without            With
      -------------------------------------------

       10Mbit/s    VC-3 (20%)    VC-12-5v (92%)
       100Mbit/s   VC-4 (67%)    VC-3-2v (100%)
       200Mbit/s   VC-4-4c(33%)  VC-3-4v (100%)
       1Gbit/s     VC-4-16c(42%) VC-4-7v (95%)

3. Physical Layer Requirements

   There are two minor modifications to the physical layer requirements
   as defined in RFC 2615 when virtually concatenated SPEs/VCs are used
   to provide transport for PPP over SONET/SDH.

   First, the path signal label (C2 byte) value for SONET/SDH STS-1/VC-3
   and above SPE/VCs is required to be the same for all constituent
   channels.  This is in contrast to the use of a single C2 byte for PPP
   transport over contiguously concatenated SONET/SDH SPE/VCs.  The
   values used for the C2 bytes should be in accordance with RFC 2615.
   For SONET VT-1.5/2/6 and SDH VC-11/12/2 the path signal label (V5
   byte bits 5-7) is required to be the same for all constituent
   channels per ITU-T G.707 [7] and ANSI T1.105.02 [6].






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   Second, for SONET/SDH STS-1/VC-3 and above SPE/VCs the multi-frame
   indicator (H4) byte will be unused for transport links utilizing
   contiguously concatenated SONET/SDH SPE/VCs.  When the concatenation
   scheme is virtual as opposed to contiguous, the H4 byte must be
   populated as per ITU-T G.707 or T1.105.02.  Similarly, for virtual
   concatenation based on SONET VT-1.5/2/6 and SDH VC-11/12/2 channels
   bit 2 of the path overhead K4 byte will be set to the value indicated
   per ITU-T G.707 [7] and ANSI T1.105.02 [6].

4. Standards Status

   ITU-T (SG13/SG15), ANSI T1X1 and ETSI TM1/WP3 have developed a global
   standard for SONET/SDH High Order and Low Order payload Virtual
   Concatenation.  This standard is defined in the following documents:

      ITU-T G.803 Architecture of transport networks based on the
      synchronous digital hierarchy (SDH)

      ITU-T G.707 Network Node Interface for the Synchronous Digital
      Hierarchy (SDH)

      ITU-T G.783 Characteristics of Synchronous Digital Hierarchy (SDH)
      Equipment Functional Blocks

      ANSI T1.105 Synchronous Optical Network (SONET) - Basic
      Description including Multiplex Structure, Rates and Formats

      ANSI T1.105.02 Synchronous Optical Network (SONET) - Payload
      Mappings

      ETSI EN 300 417-9-1 Transmission and Multiplexing (TM) Generic
      requirements of transport functionality of equipment Part 9:
      Synchronous Digital Hierarchy (SDH) concatenated path layer
      functions.  Subpart 1: Requirements

   Work in ITU-T, ANSI T1X1 and ETSI TM1/WP3 has ensured global
   standards alignment.

   With the completion of a standard for SONET/SDH SPE/VC virtual
   concatenation it is appropriate to document the use of this standard
   for PPP transport over SONET/SDH, which is the intent of this
   document.

5. Security Considerations

   The security discussion in RFC 2615 also applies to this document.
   No new security features have been explicitly introduced or removed
   compared to RFC 2615.



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6. References

   [1]   Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, RFC
         1661, July 1994.

   [2]   Simpson, W., "PPP in HDLC-like Framing", STD 51, RFC 1662, July
         1994.

   [3]   Malis, A. and W. Simpson, "PPP over SONET/SDH RFC 2615, June
         1999.

   [4]   Bellcore Publication GR-253-Core "Synchronous Optical Network
         (SONET) Transport Systems: Common Generic Criteria" January
         1999

   [5]   American National Standards Institute, "Synchronous Optical
         Network (SONET) - Basic Description including Multiplex
         Structure, Rates and Formats" ANSI T1.105-1995

   [6]   American National Standards Institute, "Synchronous Optical
         Network (SONET) - Payload Mappings" ANSI T1.105.02-1998

   [7]   ITU-T Recommendation G.707 "Network Node Interface for the
         Synchronous Digital Hierarchy" 1996

7. Acknowledgements

   We would like to acknowledge Huub van Helvoort, Maarten Vissers
   (Lucent Technologies), Paul Langner (Lucent Microelectronics), Trevor
   Wilson (Nortel Networks), Mark Carson (Nortel Networks) and James
   McKee (Nortel Networks) for their contribution to the development of
   virtual concatenation of SONET/SDH payloads.



















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8. Authors' Addresses

   Nevin Jones
   Agere Systems
   Broadband IC Systems Architecture
   Rm. 7E-321
   600 Mountain Avenue
   Murray Hill, NJ 07974

   EMail: nrjones@agere.com


   Chris Murton
   Nortel Networks Harlow Laboratories
   London Road, Harlow,
   Essex, CM17 9NA UK

   EMail: murton@nortelnetworks.com

































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9.  Full Copyright Statement

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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