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Network Working Group W A Simpson
Internet Draft Daydreamer
expires in six months September 1993
PPP over SONET/SDH
draft-ietf-pppext-sonet-01.txt
Status of this Memo
This document is the product of the Point-to-Point Protocol Working
Group of the Internet Engineering Task Force (IETF). Comments should
be submitted to the ietf-ppp@ucdavis.edu mailing list.
Distribution of this memo is unlimited.
This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas,
and its Working Groups. Note that other groups may also distribute
working documents as Internet Drafts.
Internet Drafts are draft documents valid for a maximum of six
months. Internet Drafts may be updated, replaced, or obsoleted by
other documents at any time. It is not appropriate to use Internet
Drafts as reference material or to cite them other than as a
``working draft'' or ``work in progress.''
Please check the 1id-abstracts.txt listing contained in the
internet-drafts Shadow Directories on nic.ddn.mil, nnsc.nsf.net,
nic.nordu.net, ftp.nisc.sri.com, or munnari.oz.au to learn the
current status of any Internet Draft.
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DRAFT PPP over SONET/SDH September 1993
Abstract
The Point-to-Point Protocol (PPP) [1] provides a standard method for
transporting multi-protocol datagrams over point-to-point links.
This document describes the use of PPP over Synchronous Optical
Network (SONET) and Synchronous Digital Heirarchy (SDH) circuits.
Applicability
This specification is intended for those implementations which desire
to use the PPP encapsulation over high speed private point-to-point
links, such as intra-campus single-mode fiber which may already be
installed and unused. Because the PPP encapsulation has relatively
low overhead, it is anticipated that significantly higher throughput
can be attained compared to other SONET/SDH payload mappings, at a
significantly lower cost for line termination equipment.
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1. Introduction
PPP was designed as a standard method of communicating over point-
to-point links. Initial deployment has been over short local lines,
leased lines, and plain-old-telephone-service (POTS) using modems.
As new packet services and higher speed lines are introduced, PPP is
easily deployed in these environments as well.
This specification is primarily concerned with the use of the PPP
encapsulation over SONET/SDH links. Since SONET/SDH is by definition
a point-to-point circuit, PPP is well suited to use over these links.
The Synchronous Optical Network (SONET) [3] is an octet-synchronous
multiplex scheme that defines a family of standard rates and formats.
Despite the name, it is not limited to optical links. Electrical
specifications have been defined for single-mode fiber, multi-mode
fiber, and CATV 75 ohm coaxial cable. The transmission rates are
integral multiples of 51.840 Mbps, which may be used to carry T3/E3
bit-synchronous signals. The allowed multiples are currently
specified as
STS-1 51.840 STS-18 933.120
STS-3 155.520 STS-24 1,244.160
STS-9 466.560 STS-36 1,866.240
STS-12 622.080 STS-48 2,488.320
The CCITT Synchronous Digital Heirarchy (SDH) defines a subset of
SONET transmission rates beginning at 155.520 Mbps [5].
SONET SDH equivalent
STS-3c STM-1
STS-12c STM-4
STS-48c STM-16
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2. Physical Layer Requirements
PPP treats SONET/SDH transport as octet oriented synchronous links.
SONET/SDH links are full-duplex by definition.
Interface Format
PPP presents an octet interface to the physical layer. There is
no provision for sub-octets to be supplied or accepted.
The octet stream is mapped into the SONET/SDH Synchronous Payload
Envelope (SPE), with the octet boundaries aligned with the SPE
octet boundaries.
No scrambling is needed during insertion into the SPE.
The Path Signal Label (C2) is intended to indicate the contents of
the SPE. The experimental value of 207 (cf hex) is used to
indicate PPP.
The Multiframe Indicator (H4) is currently unused, and MUST be
zero.
Transmission Rate
The basic rate for PPP over SONET/SDH is that of STS-3c/STM-1 at
155.520 Mbps. The available information bandwidth is 149.760
Mbps, which is the STS-3c/STM-1 SPE with section, line and path
overhead removed. This is the same super-rate mapping that is
used for ATM and FDDI [4].
Lower signal rates MUST use the Virtual Tributary (VT) mechanism
of SONET/SDH. This maps existing signals up to T3/E3 rates
asynchronously into the SPE, or uses available clocks for bit-
synchronous and byte-synchronous mapping.
Higher signal rates SHOULD conform to the SDH STM series, rather
than the SONET STS series, as equipment becomes available. The
STM series progresses in powers of 4 (instead of 3), and employs
fewer steps, which is likely to simplify multiplexing and
integration.
Control Signals
PPP does not require the use of control signals. When available,
using such signals can allow greater functionality and
performance. Implications are discussed in [2].
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3. Framing
The framing for octet-synchronous links is described in "PPP in HDLC
Framing" [2].
The PPP frames are located by row within the SPE payload. Because
frames are variable in length, the frames are allowed to cross SPE
boundaries.
4. Configuration Details
The standard LCP sync configuration defaults apply to SONET/SDH
links.
The following Configurations Options are recommended:
Magic Number
No Address and Control Field Compression
No Protocol Field Compression
32-bit FCS
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Security Considerations
Security issues are not discussed in this memo.
References
[1] Simpson, W. A., "The Point-to-Point Protocol (PPP)", work in
progress.
[2] Simpson, W.A., "PPP in HDLC Framing", work in progress.
[3] American National Standard for Telecommunications - Digital
Hierarchy - Optical Interface Rates and Formats Specification,
ANSI T1.105-1991.
[4] American National Standard for Telecommunications - Synchronous
Optical Network (SONET) Payload Mappings, ANSI T1.105.02-1993
draft.
[5] CCITT Recommendation G.707, "Synchronous Digital Hierarchy Bit
Rates", June 1992.
Acknowledgments
PPP over SONET was first proposed by Craig Partridge (BBN). Some
information was obtained from the good folks at Bellcore.
Technical assistance and information was also provided by Victor
Demjanenko (SUNY Buffalo).
Special thanks to Morning Star Technologies for providing computing
resources and network access support for writing this specification.
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DRAFT PPP over SONET/SDH September 1993
Chair's Address
The working group can be contacted via the current chair:
Fred Baker
Advanced Computer Communications
315 Bollay Drive
Santa Barbara, California, 93111
EMail: fbaker@acc.com
Author's Address
Questions about this memo can also be directed to:
William Allen Simpson
Daydreamer
Computer Systems Consulting Services
1384 Fontaine
Madison Heights, Michigan 48071
EMail: Bill.Simpson@um.cc.umich.edu
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DRAFT PPP over SONET/SDH September 1993
Table of Contents
1. Introduction .......................................... 1
2. Physical Layer Requirements ........................... 2
3. Framing ............................................... 3
4. Configuration Details ................................. 3
SECURITY CONSIDERATIONS ...................................... 4
REFERENCES ................................................... 4
ACKNOWLEDGEMENTS ............................................. 4
CHAIR'S ADDRESS .............................................. 5
AUTHOR'S ADDRESS ............................................. 5