RFC 1619

PPP over SONET/SDH

📅 published May 1994, from ietf

RFC 1619: PPP over SONET/SDH 🎀

Okay bestie, here's the deal. This is an RFC, which is basically a spec document the Internet runs on. It's from May 1994, it was written by W. Simpson of Daydreamer for the Network Working Group, and it's a Standards Track document. 🦋 It doesn't say it obsoletes or updates anything, so it's not replacing or patching any older RFCs. Totally clean. 💅

Status of this Memo ✨

Hey, so this document is a standards track protocol spec for the Internet community. It's basically an invitation to talk about it and suggest improvements. 💬 If you want to know where it stands officially, go check the current "Internet Official Protocol Standards" document (STD 1). Also, you can share this memo as much as you want, because distribution is unlimited. 🌈

Abstract 🦋

The Point-to-Point Protocol (PPP) [1] is the go-to method for sending multi-protocol datagrams over point-to-point links. 💜 This document explains how to run PPP over Synchronous Optical Network (SONET) and Synchronous Digital Heirarchy (SDH) circuits. ✨

This doc came out of the Point-to-Point Protocol Working Group of the IETF. If you have comments, send them to the ietf-ppp@merit.edu mailing list. 📬

Applicability 🌸

This spec is for implementations that want PPP encapsulation on high-speed private point-to-point links. Think intra-campus single-mode fiber that's probably already installed and just sitting there unused. 🍓

PPP encapsulation has pretty low overhead, so it's expected to reach a lot higher throughput compared to other SONET/SDH payload mappings. Bonus: the line termination equipment costs a lot less. It's giving efficiency. 🔥

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 built to be a standard way of talking over point-to-point links. It started out on short local lines, leased lines, and plain-old-telephone-service (POTS) with modems. 📞 As newer packet services and faster lines showed up, PPP fit right in there too. Iconic. 👑

This spec is mostly about using PPP encapsulation over SONET/SDH links. SONET/SDH is a point-to-point circuit by definition, so PPP is a perfect match. 🫶

SONET [3] is an octet-synchronous multiplex scheme that defines a family of standard rates and formats. Fun fact: despite the name, it isn't only for optical links. There are electrical specs for single-mode fiber, multi-mode fiber, and CATV 75 ohm coaxial cable. ⭐ The transmission rates are integral multiples of 51.840 Mbps, and those can 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) is a subset of SONET rates that starts at 155.520 Mbps [5]. 🧚 Here's how they line up:

        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. And SONET/SDH links are full-duplex by definition, so they go both ways. 💅

Interface Format 🦋

PPP shows an octet interface to the physical layer. Sub-octets aren't a thing here, nothing to supply and nothing to accept. 🙈

The octet stream gets mapped into the SONET/SDH Synchronous Payload Envelope (SPE), and the octet boundaries line up with the SPE octet boundaries. ✨

No scrambling is needed when you insert into the SPE. 🌈

The Path Signal Label (C2) is meant to show what's inside the SPE. The experimental value 207 (hex) means PPP. 🔥

The Multiframe Indicator (H4) is currently unused, and it MUST be zero. 🍓

Transmission Rate 💜

The basic rate for PPP over SONET/SDH is STS-3c/STM-1, which runs at 155.520 Mbps. The information bandwidth you actually get is 149.760 Mbps, which is the STS-3c/STM-1 SPE with section, line and path overhead taken out. This is the same super-rate mapping ATM and FDDI use [4]. Iykyk. 😭

Lower signal rates MUST use the Virtual Tributary (VT) mechanism of SONET/SDH. It 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 goes up in powers of 4 instead of 3, and it has fewer steps, which is likely to make multiplexing and integration simpler. Main character energy. 👑

Control Signals 🌸

PPP doesn't require control signals. When they're available, though, they can unlock more functionality and performance. The implications are discussed in [2]. ✨

3. Framing 🦋

The framing for octet-synchronous links is described in "PPP in HDLC Framing" [2]. 💖

PPP frames are located by row within the SPE payload. Frames are variable in length, so they're 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. 💀 Yes, you read that right. The spec itself doesn't address security at all, so take that seriously and plan around it. ⚠️

Warning, bestie: this memo does not discuss security. Don't assume it's covered just because the protocol works. 🚨

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 came from the good folks at Bellcore. 🌸

Technical assistance and information also came from Victor Demjanenko (SUNY Buffalo). 🫶

Special thanks to Morning Star Technologies for providing computing resources and network access support for writing this spec. 🎀

Chair's Address 💜

The working group can be reached through 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 go 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
📦 where this page comes from