Network Working Group N. Jones

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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RFC 3255 Extending PPP over SONET/SDH April 2002

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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RFC 3255 Extending PPP over SONET/SDH April 2002

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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RFC 3255 Extending PPP over SONET/SDH April 2002

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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RFC 3255 Extending PPP over SONET/SDH April 2002

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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RFC 3255 Extending PPP over SONET/SDH April 2002

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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RFC 3255 Extending PPP over SONET/SDH April 2002

8. Authors' Addresses

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

EMail: [email protected]

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

EMail: [email protected]

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RFC 3255 Extending PPP over SONET/SDH April 2002

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
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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
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English.

The limited permissions granted above are perpetual and will not be
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This document and the information contained herein is provided on an
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Acknowledgement

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

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