PPP over SONET/SDH
Running PPP over fiber-optic SONET and SDH circuits.
Simpson, W., "PPP over SONET/SDH", RFC 1619, DOI 10.17487/RFC1619, May 1994, <https://www.rfc-editor.org/info/rfc1619>.
@misc{rfc1619,
series = {Request for Comments},
number = 1619,
howpublished = {RFC 1619},
publisher = {RFC Editor},
doi = {10.17487/RFC1619},
url = {https://www.rfc-editor.org/info/rfc1619},
author = {W. Simpson},
title = {{PPP over SONET/SDH}},
pagetotal = 5,
year = 1994,
month = may,
} RFC text
Contents
Network Working Group W. Simpson
Request for Comments: 1619 Daydreamer
Category: Standards Track May 1994
PPP over SONET/SDH
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.
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.
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@merit.edu mailing list.
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.
Table of Contents
1. Introduction .......................................... 1
2. Physical Layer Requirements ........................... 1
3. Framing ............................................... 2
4. Configuration Details ................................. 3
SECURITY CONSIDERATIONS ...................................... 3
REFERENCES ................................................... 3
ACKNOWLEDGEMENTS ............................................. 3
CHAIR'S ADDRESS .............................................. 4
AUTHOR'S ADDRESS ............................................. 4
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
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].
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 Configuration Options are recommended:
Magic Number
No Address and Control Field Compression
No Protocol Field Compression
32-bit FCS
Security Considerations
Security issues are not discussed in this memo.
References
[1] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", RFC
1548, Daydreamer, December 1993.
[2] Simpson, W., Editor, "PPP in HDLC Framing", RFC 1549,
Daydreamer, December 1993.
[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.
Chair's Address
The working group can be contacted via the current chair:
Fred Baker
Advanced Computer Communications
315 Bollay Drive
Santa Barbara, California 93117
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
bsimpson@MorningStar.com
AI ELI5
On this page
§1PPP over Fiber-Optic Lines
The Point-to-Point Protocol (PPP) is a standard for transmitting multi-protocol data over point-to-point links. Originally deployed on dial-up modems and leased phone lines, PPP works equally well over high-speed fiber circuits. SONET (Synchronous Optical Network) and SDH (Synchronous Digital Hierarchy) are fiber-based transmission standards used by telephone carriers, with transmission rates from 51.840 Mbps up to 2.488 gigabits per second.
This RFC describes how to run PPP directly over SONET and SDH circuits, allowing carriers to use PPP's simple encapsulation for private point-to-point fiber links. The lightweight overhead of PPP enables higher throughput than alternative SONET payload mappings.
PPP is a simple protocol designed for point-to-point links. SONET and SDH are fiber-optic circuits that carriers use. This RFC shows how to put one inside the other.
§2Physical Layer Mapping
PPP presents an octet-oriented synchronous interface to the physical layer. The octet stream is mapped into the SONET/SDH Synchronous Payload Envelope (SPE), with octet boundaries aligned to SPE boundaries. No scrambling is applied during insertion.
The Path Signal Label (C2 byte) is set to the experimental value 207 (hex cf) to indicate PPP content. The basic transmission rate is STS-3c/STM-1 at 155.520 Mbps, providing 149.760 Mbps of available information bandwidth. Lower rates use SONET/SDH Virtual Tributary mechanisms to map existing signals asynchronously or with byte-synchronous methods.
PPP data gets put directly into the fiber's payload space, like packing boxes into a truck. The label on the truck says it contains PPP.
§3Framing and Configuration
The framing for PPP over octet-synchronous links uses HDLC framing. PPP frames are variable in length and can cross SPE boundaries, allowing efficient use of the link. Configuration uses standard LCP (Link Control Protocol) defaults, with recommended options including Magic Number, 32-bit frame check sequence (FCS), and no address/control or protocol field compression.
PPP does not require control signals from the physical layer. When available, such signals can improve functionality and performance.
PPP breaks data into variable-length frames that can wrap around the fiber payload boundaries. The setup is simple and uses the standard PPP defaults.