Subject: Re-send of Extending PPP with virtual concatenation

From: "Nevin R. Jones" <[email-masked]>
Date: Mon, 03 Jul 2000 14:14:57 -0400

All:

Attached is an upload of the above internet draft. Any comments are
welcome.

Regards,

-Nevin Jones

PPP Extensions Working Group                                 N. Jones,
INTERNET DRAFT                                 Lucent Microelectronics
Category: Informational                                     C. Murton,
Expires: December 2000                                 Nortel Networks
                                                             June 2000
							    R. Broberg,
					       	   Lucent Technologies
					       Optical Networking Group

                       Extending PPP over SONET/SDH,
       with virtual concatenation, high order and low order payloads
                   <draft-ietf-pppext-posvcholo-02.txt>

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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   Distribution of this draft is unlimited.

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Abstract

   The RFC 1661 Point-to-Point Protocol (PPP) [1] provides a standard
   method for transporting multi-protocol datagrams over point-to-point
   links. The RFC 1662 PPP in HDLC-like Framing [2] and RFC 2615 PPP
   over SONET/SDH (POS) [3] documents describe the use of PPP over
   Synchronous Optical Network (SONET) and Synchronous Digital
   Hierarchy (SDH) circuits.

   This document proposes an extension to the mapping of PPP into
   SONET/SDH defined in RFC 2615 PPP over SONET/SDH (POS) [3], to
   include use of SONET/SDH SPE/VC virtual concatenation and use of
   both high order and low order payloads. The objective of this
   document is to provide the status of this proposal in the
   telecommunications standards definition process. The current
   situation is that work in ANSI, ETSI & ITU-T has resulted in a
   global standard for virtual concatenation.

   This document is the product of the Point-to-Point Protocol
   Extensions Working Group of the Internet Engineering Task Force
   (IETF). Comments should be submitted to the [email-masked]
   mailing list.

Table of Contents

   1.    Introduction................................................3

   2.    Rate Comparisons............................................4

   3.    Current Technologies........................................6

   4.    Virtual Concatenation Description...........................7

   5.    Emerging Benefits...........................................8

   6.    Standards Status............................................9

   7.    Security Considerations....................................10

   8.    References.................................................10

   9.    Acknowledgments............................................11

   10.   Author's Addresses.........................................11

   11.   Copyright Notice...........................................11

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1. Introduction

   A broad consensus has emerged among major market researchers
   indicating, that while voice traffic will continue to grow at a
   moderate clip, data will come to dominate most networks by the years
   2002-2005. Moreover, recent network studies [4][5] have shown that
   this data traffic is overwhelmingly dominated by relatively short IP
   datagrams transported across network sessions that are in the tens
   of seconds duration range.

   In the face of the above trends, it is becoming increasingly more
   obvious that, although the existing SONET/SDH transport structures
   are sufficiently optimized to support traditional TDM voice type
   applications, they are bandwidth inefficient when confronted with
   the inherently bursty, statistical characteristics of data
   applications.

   In addition, new applications requiring transport in SONET/SDH
   concatenated payload envelopes run the risk of being unsupported.
   This is a result of the non-standardization and, consequently, non-
   availability of particular rates (e.g. SONET STS-2c, STS-4c, STS-24c
   or SDH VC-2-2c) or the unavailability in practice of particular
   concatenation rates even if they were standardized (e.g., STS-12c in
   SONET or VC-4-4c in SDH).

   Furthermore, even if the concatenated rates were defined in
   standards and supported by the network operator, the practical
   availability of such payload coverage is often dependent upon the
   non-fragmentation (i.e., the availability of contiguous time slots)
   of bandwidth in the SONET/SDH network.

   The SONET/SDH standards have been updated to include the mechanism
   for SONET/SDH payload virtual concatenation. This scheme can provide
   right sized link channelisation for ring and other SONET/SDH network
   topologies.

   The ITU-T has developed a standard for SDH High Order and Low Order
   payload Virtual Concatenation. This global standards development has
   been aligned with ANSI T1X1 (SONET) and ETSI.

   Further standards work on the subject of Variable Bandwidth
   Allocation (VBA) will make the dynamic re-sizing and hitless re-
   configuration of virtually concatenated paths possible.

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   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 payload               C-3
      STS-3c frame                STM-1 frame, AU-4
      STS-3c-SPE                  VC-4
      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 [6], ANSI T1.105 [7], ANSI T1.105.02 [8] and
   ITU-T G.707 [9].

2. Rate Comparisons

   The original tributary bit rates chosen for SONET/SDH were intended
   for voice services. These rates have a coarse granularity, require
   duplicate network resources for protection and are not a good match
   to LAN bandwidths.

   Currently supported WAN bandwidth links for PPP:

        ANSI                   ETSI
     -----------------------------------------------------
       DS1 (1.5Mbit/s)        E1 (2Mbit/s)
       DS3 (45Mbit/s)         E3 (34Mbit/s)
       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)

   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 :

         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

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         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.

   At present CONTIGUOUS concatenation caters for 4 or 16 VC-4s.

   Bit rates for Transparent LAN Services (TLS) are typically 10Mbit/s
   and 100Mbit/s. Bit rates of 1Gbit/s are also becoming more and more
   popular. Also other services (e.g. ATM cells stream) may vary from a
   few Mbit/s to several tens of Mbit/s. However there are no direct
   mappings for the transport of such bit rates over SONET/SDH.

   In order to transport the services mentioned above via a SONET/SDH
   transport network there is no match in the bandwidth granularity.

   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.

   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 and STS-48c SPE = 2,396.160 Mbit/s.

                  Table 1. SONET Virtual Concatenation

      Bit rate     Without            With
     -------------------------------------------------------------
      10Mbit/s    STS-1 (20%)   VT-1.5-7v (89%)
      25Mbit/s    STS-1 (50%)   VT-1.5-16v(98%)
      100Mbit/s   STS-3c (67%)  STS-1-2v (100%) or VT-1.5-63v (99%)
      200Mbit/s   STS-12c(33%)  STS-1-4v (100%) or STS-3c-2v (66%)
      1Gbit/s     STS-48c(42%)  STS-3c-7v (95%)

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   Similarly, Table 2, contains SDH transport signals with the
   following effective payload capacity: VC-11 = 1.600 Mbit/s, VC-12 =
   2.176 Mbit/s, VC-2 = 6.784 Mbit/s, VC-3 = 48.960 Mbit/s, VC-4 =
   149.760 Mbit/s and VC-4-4c = 599.040 Mbit/s.

                 Table 2. SDH Virtual Concatenation

      Bit rate     Without            With
     -------------------------------------------------------------
      10Mbit/s    VC-3 (20%)    VC-12-5v (92%)
      25Mbit/s    VC-3 (50%)    VC-12-12v (96%)
      100Mbit/s   VC-4 (67%)    VC-3-2v (100%) or VC-12-46v (100%)
      200Mbit/s   VC-4-4c(33%)  VC-3-4v (100%) or VC-4-2v (66%)
      1Gbit/s     VC-4-16c(42%) VC-4-7v (95%)

   The only currently supported SONET/SDH SPE/VCs in RFC 2615 [4] 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.

3. Current Technologies

   Two existing standard technologies for making use of multiple
   physical paths to build a single logical link are Multi-link PPP
   (ML-PPP RFC 1990 [10]) and Inverse Multiplexing for ATM (IMA af-phy-
   0086.001 [11]). These approaches use frame/cell level load balancing
   and typically use multiple T1/E1 paths to build a link.

   Virtual concatenation uses SONET/SDH SPE/VC directly and therefore
   does not have the inefficiency of mapping into asynchronous (T1/T3)
   or plesiochronous (E1/E3) payload first. In addition since virtual
   concatenation is a byte level inverse multiplexing technique, it has
   the characteristics of right sized bandwidth, improved granularity,
   cost, low delay, low jitter, re-use of protection bandwidth and high
   efficiency payload mapping. This makes it a suitable physical layer
   for a single PPP link. Note that virtual concatenation can also be
   of benefit for ATM for much the same reasons.

   SONET/SDH virtual concatenation operates at the physical layer below
   PPP. The main objective of virtual concatenation is to provide a

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   logical mesh of multiple right sized channels over a SONET/SDH
   network. It is therefore independent of any higher layer schemes for
   providing equal cost multi-path routing or load balancing.

4. Virtual Concatenation Description

   This section describes Concatenation of Virtual Containers and in
   particular describes Virtual Concatenation.

   Concatenation is a method for the transport, over SONET/SDH
   networks, of a payload of a bandwidth greater than the capacity of
   the information structure currently defined in standards. For
   example to transport a signal of bandwidth equivalent to four VC-4s
   the frame structure would be VC-4-4c.

   Concatenation is defined in ITU-T recommendation G.707 [9] as "A
   procedure whereby a multiplicity of Virtual Containers is associated
   one with another with the result that their combined capacity can be
   used as a single container across which bit sequence integrity is
   maintained". Two types of concatenation are proposed: contiguous and
   virtual.

   Contiguous concatenation

   Contiguous concatenation uses a concatenation indicator in the
   pointer associated with each concatenated frame to indicate that the
   SPE/VC with which the pointers are associated are concatenated.

   For example, four VC-4s contiguously concatenated in an information
   structure would have a data rate of VC-4-4C. The resulting signal
   has one valid path overhead (9-byte column) and three 9-byte columns
   of fixed stuff. The four payloads are byte interleaved in the VC-4-
   4c payload area.

   For contiguously concatenated payload to pass through a network, all
   intermediate nodes must support contiguous concatenation.

   Virtual Concatenation

   Many installed network elements in SONET/SDH networks cannot support
   contiguous concatenation. The processing in these NEs is limited to
   processing only individual SPE/VC. To implement contiguous
   concatenation in such networks would require extensive hardware
   upgrade of the equipment and would be prohibitively expensive.

   Virtual Concatenation is one way of overcoming this problem. The
   main aim of virtual concatenation is to provide the SONET/SDH NEs at
   both ends of the signal path with the capability of
   sending/receiving individual SPE/VC that are associated in a
   concatenated group. In this way the cost of transporting
   concatenated signal is confined to the up-grade costs at the ends of
   the path. These cost are likely to be significantly lower than up-
   grading a whole network to handle contiguously concatenated signals.

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   At the sending end it will be necessary to provide each SPE/VC with
   information about its concatenated group identity and its
   position/sequence within the group, and to give each its own POH for
   processing in the intermediate nodes in the network. At the
   receiving end the equipment must be capable of identifying a SPE/VC
   as belonging to a particular concatenated group and identifying its
   position/sequence within that group. Because of the likelihood of
   different propagation and processing delays for each of the
   individual SPE/VC, it will be necessary for the receiving end
   equipment to provide buffers to store the incoming data until the
   latest SPE/VC arrives, when re-alignment can be performed.

   One method of providing group identification is to use the J1 byte
   (Path Trace). If each concatenated group used a different path trace
   identifier then the receiving equipment will know that a particular
   VC belongs to that group.

   The information of what sequence/position a SPE/VC has within the
   group must be conveyed in the POH. The receiving end will process
   this information and re-assemble the SPE/VC in the correct order.

   The difference in the arrival times at the receiver of given
   SPEs/VCs in a virtually concatenated group is known as the
   Differential Delay. It will be necessary for the receiving equipment
   to measure this parameter and to detect if it has gone beyond the
   range of the buffers, which have been provided to re-align the
   incoming data.

   Network Management of the virtually concatenated signal will not
   require the network equipment to be modified since the NEs are
   processing essentially standard SPE/VC.

5. Emerging Benefits

   The main objective of virtual concatenation is to provide multiple
   right sized channels over a SONET/SDH network.

   The benefit of virtual concatenation to PPP is the ability to
   provide channels in a SONET/SDH network that are more appropriate
   for IP. The advantages of these channels are bandwidth granularity,
   right sized capacity, efficient mapping into SONET/SDH SPE/VC,
   traffic scalability and channelized high capacity SONET/SDH
   interfaces.

   The characteristics of virtually concatenated links, which provide
   for bandwidth reduction in the event of a path failure, are a good
   match for Differentiated Services. The reason for this is that the
   loss of bandwidth will effect the lower priority traffic first and
   should allow the higher priority traffic to continue passing over
   the link.

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   Another benefit of virtual concatenation is the ability to add or
   remove a SPE/VC from the group without taking a PPP link using the
   group Out Of Service. The change in bandwidth should take place in a
   few milli-seconds, depending on the physical distance between the
   two ends of the link.

   Virtual concatenation could make better use of SONET/SDH path
   protection bandwidth. Consider a single path protected 45Mbit/s or
   34Mbit/s circuit. The SONET/SDH bandwidth needed to support this
   would involve using two STS-1/VC-3s. When virtual concatenation is
   applied to this situation, a link of 100Mbit/s can be provided. In
   the event of a path failure this would be reduced to 50Mbit/s.

6. Standards Status

   ITU-T (SG13/SG15), ANSI T1X1 and ETSI TM1/WP3 have developed global
   standards for SONET/SDH High Order and Low Order payload Virtual
   Concatenation. These changes will appear in the following standards:

        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.

   The completion of a standard for SONET/SDH SPE/VC virtual
   concatenation means it has become appropriate to consider the use of
   this standard for PPP. This could take the form of a backward
   compatible update to RFC 2615 [3].

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7. Security Considerations

   This document is for information only. Any protocol related
   documents that arise from it would contain security consideration.

8. References

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

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

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

   [4]   K. Thompson, G. Miller, and R. Wilder, "Wide Area Internet
   Traffic Patterns and Characteristics" IEEE Network, Nov 1997.
   http://www.vbns.net/presentations/papers/MCItraffic.ps

   [5]   K Claffy, Greg Miller, and Kevin Thompson, "The nature of the
   beast: Recent traffic measurements from an Internet backbone",
   INET'98 Conference, April 1998.
   http://www.caida.org/Papers/Inet98/index.html

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

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

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

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

   [10]   Sklower, K. et al., "The PPP Multilink Protocol (MP)" RFC
   1990, August 1996

   [11]   Inverse Multiplexing for ATM (IMA) Specification version 1.1
   af-phy-0086.001, March 1999

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9. Acknowledgments

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

10. Author's Addresses

   Nevin Jones
   Lucent Technologies Microelectronics Group
   600 Mountain Avenue 
   Murray Hill, New Jersey 07974 USA
   Email: [email-masked]

   Chris Murton
   Nortel Networks Harlow Laboratories
   London Road, Harlow,
   Essex, CM17 9NA UK
   Email: [email-masked]

   Robert Broberg
   Lucent Technologies Optical Networking Group
   600 Mountain Avenue 
   Murray Hill, New Jersey 07974 USA
   Email: [email-masked]

11. Copyright Notice

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