RFC 3255

Extending Point-to-Point Protocol (PPP) over Synchronous Optical NETwork/Synchronous Digital Hierarchy (SONET/SDH) with virtual concatenation, high order and low order payloads

📅 published April 2002, from ietf

Extending PPP over SONET/SDH with Virtual Concatenation 🦋

Okay bestie, let's talk about RFC 3255 💖. It's a Standards Track document from April 2002, and it's titled Extending Point-to-Point Protocol (PPP) over Synchronous Optical NETwork/Synchronous Digital Hierarchy (SONET/SDH) with virtual concatenation, high order and low order payloads. It came out of the Network Working Group and has two authors: N. Jones (Nevin Jones) from Agere Systems and C. Murton (Chris Murton) from Nortel Networks. The title block doesn't list anything it obsoletes or updates, so it's not replacing or changing any other RFC 🌸.

Status of this Memo ✨

This document is an Internet standards track protocol for the Internet community, and it asks for discussion and suggestions for improvements 🫶. For the current standardization state and status of this protocol, check the current edition of the "Internet Official Protocol Standards" (STD 1). Distribution of this memo is unlimited 🌈.

Copyright Notice 💅

Abstract 🎀

This document is an extension to the way PPP gets mapped into SONET/SDH. It adds SONET/SDH SPE/VC virtual concatenation, and it covers using 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 💖

Okay so, right now PPP over SONET/SDH has a problem 😭. Current implementations are required to select transport structures from a pretty small list of contiguously concatenated signals. Not a lot of choice, honestly.

The only SONET/SDH SPE/VCs that RFC 2615 [3] currently supports are these:

      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

Heads up: VC-4-4c and above aren't widely supported in SDH networks right now 🙈.

This is where virtual concatenation comes in and saves the day ✨. It means you can pick the right size of SONET/SDH bandwidth for your PPP links, which is so much more flexible 👑.

For your reference, here are the equivalent terms, side by side 🍓:

      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 one in RFC 2615 [3]. If you want more detail on these terms, look at Bellcore GR-253-CORE [4], ANSI T1.105 [5], ANSI T1.105.02 [6] and ITU-T G.707 [7] 🦋.

2. Rate Comparisons 🌸

These are the WAN bandwidth links you can use for PPP over SONET/SDH right now 💅:

     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 aren't generally available in SDH networks at the moment 🙈.

With virtual concatenation, these extra WAN bandwidth links would be available for PPP over SONET/SDH. It's giving main character energy 🔥:

    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 they're not necessarily useful. Lower levels are defined in the telecom standards too, for when you need them 🌈.

Okay, now the tables. Table 1 and Table 2 show the SONET/SDH transport structures you can use for different popular bit rates ✨. Each table has three columns. The first one shows the bit rate of the service you're carrying. The next column has two values: (a) the logical signals that are currently available for that transport, and (b) in parentheses, the percent efficiency of that transport signal without virtual concatenation. The last column also has two values: (a) the logical signals available, and (b) in parentheses, the percent efficiency with virtual concatenation 💖.

Quick note on Table 1: it has SONET transport signals with these effective payload capacities: 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%)

Table 2 is the SDH version 🍓. It has SDH transport signals with these effective payload capacities: 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 🧚

Here's the tea ☕: there are two minor changes to the physical layer requirements from RFC 2615 when you use virtually concatenated SPEs/VCs to carry PPP over SONET/SDH 🦋.

First, the path signal label (C2 byte) for SONET/SDH STS-1/VC-3 and above SPE/VCs is required to be the same for all the constituent channels. That's different from PPP over contiguously concatenated SONET/SDH SPE/VCs, which uses one C2 byte. The values 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 also required to be the same for all constituent channels, per ITU-T G.707 [7] and ANSI T1.105.02 [6] 🔥.

Second, for SONET/SDH STS-1/VC-3 and above SPE/VCs, the multi-frame indicator (H4) byte is unused for transport links that use contiguously concatenated SONET/SDH SPE/VCs. When the concatenation is virtual instead of 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 gets set to the value indicated per ITU-T G.707 [7] and ANSI T1.105.02 [6] 💜.

More to come in part 2! 💖

9. Full Copyright Statement 🎀✨

okay so this part is the legal bit, and bestie, I'm not gonna pretend it's the most thrilling read 💀 but it's kinda iconic how clearly it lays out what you can and can't do with the document 🫶

Here's the vibe: you're allowed to copy this document and share it with others 🦋 You can also make derivative works that comment on it, explain it, or help people implement it, and you can publish and distribute those too, in whole or in part, with no real restrictions 🌸 The one catch is that the copyright notice and this paragraph have to stay on every copy and derivative work 🔥

Now the document itself can't be changed in any way 🙈 No deleting the copyright notice, no scrubbing out the references to the Internet Society or other Internet organizations. The exceptions are if you need it for developing Internet standards (in which case you have to follow the copyright procedures in the Internet Standards process 👑) or if you're translating it into a language other than English 🌈

The permissions above are perpetual, which means they're forever ✨ The Internet Society and its successors or assigns won't revoke them 💜

Last but not least, this whole document and everything in it is provided "AS IS" 🍓 THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT USING THE INFORMATION WILL NOT INFRINGE ANY RIGHTS, AND ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE 😭

Acknowledgement 🧚

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

That's a wrap on RFC 3255 🌈 Literally the whole thing, slay 👑🦋

📦 where this page comes from

ietf: rfc3255 2002-04
💖 girlified by claude-haiku-5-5 on 2026-10-16: a language model's rewrite of the original, under its terms