PPP Extensions Working Group N. Jones,
INTERNET DRAFT Lucent Microelectronics
Category: Informational C. Murton,
Expires: June 2000 Nortel Networks
December 1999
Extending PPP over SONET/SDH,
with virtual concatenation, high order and low order payloads
<draft-ietf-pppext-posvcholo-01.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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".
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind.
Distribution of this draft is unlimited.
Jones Expires June 2000 1
Internet Draft POS with VC, HO & LO December 1999
Abstract
The RFC 1661 Point-to-Point Protocol (PPP) [1] provides a standard
method for transporting multi-protocol datagrams over point-to-point
links. The RFC 1662 PPP in HDLC-like Framing [2] and RFC 2615 PPP
over SONET/SDH (POS) [3] documents describe the use of PPP over
Synchronous Optical Network (SONET) and Synchronous Digital
Hierarchy (SDH) circuits.
This document proposes an extension to the mapping of PPP into
SONET/SDH defined in RFC 2615 PPP over SONET/SDH (POS) [3], to
include use of SONET/SDH SPE/VC virtual concatenation and use of
both high order and low order payloads. The objective of this
document is to provide the status of this proposal in the
telecommunications standards definition process.
This document is the product of the Point-to-Point Protocol
Extensions Working Group of the Internet Engineering Task Force
(IETF). Comments should be submitted to the ietf-ppp@merit.edu
mailing list.
Table of Contents
1. Introduction................................................3
2. Rate Comparisons............................................4
3. Current Technologies........................................6
4. Virtual Concatenation Description...........................7
5. Emerging Benefits...........................................8
6. Standards Status............................................9
7. Security Considerations.....................................9
8. References..................................................9
9. Acknowledgments............................................10
10. Author's Addresses.........................................11
11. Copyright Notice...........................................11
Jones Expires June 2000 2
Internet Draft POS with VC, HO & LO December 1999
1. Introduction
A broad consensus has emerged among major market researchers
indicating, that while voice traffic will continue to grow at a
moderate clip, data will come to dominate most networks by the years
2002-2005. Moreover, recent network studies [4][5] have shown that
this data traffic is overwhelmingly dominated by relatively short IP
datagrams transported across network sessions that are in the tens
of seconds duration range.
In the face of the above trends, it is becoming increasingly more
obvious that, although the existing SONET/SDH transport structures
are sufficiently optimized to support traditional TDM voice type
applications, they are bandwidth inefficient when confronted with
the inherently bursty, statistical characteristics of data
applications.
In addition, new applications requiring transport in SONET/SDH
concatenated payload envelopes run the risk of being unsupported.
This is a result of the non-standardization and, consequently, non-
availability of particular rates (e.g. SONET STS-2c, STS-4c, STS-24c
or SDH VC-2-2c) or the unavailability in practice of particular
concatenation rates even if they were standardized (e.g., STS-12c in
SONET or VC-4-4c in SDH).
Furthermore, even if the concatenated rates were defined in
standards and supported by the network operator, the practical
availability of such payload coverage is often dependent upon the
non-fragmentation (i.e., the availability of contiguous time slots)
of bandwidth in the SONET/SDH network.
Work is in progress to modify SONET/SDH standards. This will allow
support for payload virtual concatenation that can provide the
necessary link channelisation for ring and other network topologies.
It will also make the dynamic re-sizing and hitless re-configuration
of paths possible.
The ITU-T is in the process of developing a standard for SDH High
Order and Low Order payload Virtual Concatenation. This global
standards development has been widely supported within ANSI T1X1
(SONET) and ETSI.
Jones Expires June 2000 3
Internet Draft POS with VC, HO & LO December 1999
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 payload C-3
STS-3c frame STM-1 frame, AU-4
STS-3c-SPE VC-4
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 [6], ANSI T1.105 [7], ANSI T1.105.02 [8] and
ITU-T G.707 [9].
2. Rate Comparisons
The original tributary bit rates chosen for SONET/SDH were intended
for voice services. These rates have a coarse granularity, require
duplicate network resources for protection and are not a good match
to LAN bandwidths.
Currently supported WAN bandwidth links for PPP:
ANSI ETSI
-----------------------------------------------------
DS1 (1.5Mbit/s) E1 (2Mbit/s)
DS3 (45Mbit/s) E3 (34Mbit/s)
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)
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 :
SONET
VT-1.5 (1-84) 1.6Mbit/s-134Mbit/s
STS-1 (1-64) 49Mbit/s-3.1Gbit/s
STS-3c (1-64) 150Mbit/s-10Gbit/s
Jones Expires June 2000 4
Internet Draft POS with VC, HO & LO December 1999
SDH
VC-12 (1-63) 2.2Mbit/s-137Mbit/s
VC-3 (1-64) 49Mbit/s-3.1Gbit/s
VC-4 (1-64) 150Mbit/s-10Gbit/s
Higher levels of virtual concatenation are possible, but not
necessarily useful.
At present CONTIGUOUS concatenation caters for 4 or 16 VC-4s.
Bit rates for Transparent LAN Services (TLS) are typically 10Mbit/s
and 100Mbit/s. Bit rates of 1Gbit/s are also becoming more and more
popular. Also other services (e.g. ATM cells stream) may vary from a
few Mbit/s to several tens of Mbit/s. However there are no direct
mappings for the transport of such bit rates over SONET/SDH.
In order to transport the services mentioned above via a SONET/SDH
transport network there is no match in the bandwidth granularity.
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.
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 and STS-48c SPE = 2,396.160 Mbit/s.
Table 1. SONET Virtual Concatenation
Bit rate Without With
-------------------------------------------------------------
10Mbit/s STS-1 (20%) VT-1.5-7v (89%)
25Mbit/s STS-1 (50%) VT-1.5-16v(98%)
100Mbit/s STS-3c (67%) STS-1-2v (100%) or VT-1.5-63v (99%)
200Mbit/s STS-12c(33%) STS-1-4v (100%) or STS-3c-2v (66%)
1Gbit/s STS-48c(42%) STS-3c-7v (95%)
Similarly, Table 2, contains SDH transport signals with the
following effective payload capacity: VC-11 = 1.600 Mbit/s, VC-12 =
2.176 Mbit/s, VC-2 = 6.784 Mbit/s, VC-3 = 48.960 Mbit/s, VC-4 =
149.760 Mbit/s and VC-4-4c = 599.040 Mbit/s.
Jones Expires June 2000 5
Internet Draft POS with VC, HO & LO December 1999
Table 2. SDH Virtual Concatenation
Bit rate Without With
-------------------------------------------------------------
10Mbit/s VC-3 (20%) VC-12-5v (92%)
25Mbit/s VC-3 (50%) VC-12-12v (96%)
100Mbit/s VC-4 (67%) VC-3-2v (100%) or VC-12-46v (100%)
200Mbit/s VC-4-4c(33%) VC-3-4v (100%) or VC-4-2v (66%)
1Gbit/s VC-4-16c(42%) VC-4-7v (95%)
The only currently supported SONET/SDH SPE/VCs in RFC 2615 [4] 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.
3. Current Technologies
Two existing standard technologies for making use of multiple
physical paths to build a single logical link are Multi-link PPP
(ML-PPP RFC 1990 [10]) and Inverse Multiplexing for ATM (IMA af-phy-
0086.001 [11]). These approaches use frame/cell level load balancing
and typically use multiple T1/E1 paths to build a link.
Virtual concatenation uses SONET/SDH SPE/VC directly and therefore
does not have the inefficiency of mapping into asynchronous (T1/T3)
or plesiochronous (E1/E3) payload first. In addition since virtual
concatenation is a byte level inverse multiplexing technique, it has
the characteristics of right sized bandwidth, improved granularity,
cost, low delay, low jitter, re-use of protection bandwidth and high
efficiency payload mapping. This makes it a suitable physical layer
for a single PPP link. Note that virtual concatenation can also be
of benefit for ATM for much the same reasons.
SONET/SDH virtual concatenation operates at the physical layer below
PPP. The main objective of virtual concatenation is to provide a
logical mesh of multiple right sized channels over a SONET/SDH
network. It is therefore independent of any higher layer schemes for
providing equal cost multi-path routing or load balancing.
Jones Expires June 2000 6
Internet Draft POS with VC, HO & LO December 1999
4. Virtual Concatenation Description
This section describes Concatenation of Virtual Containers and in
particular describes Virtual Concatenation.
Concatenation is a method for the transport, over SONET/SDH
networks, of a payload of a bandwidth greater than the capacity of
the information structure currently defined in standards. For
example to transport a signal of bandwidth equivalent to four VC-4s
the frame structure would be VC-4-4c.
Concatenation is defined in ITU-T recommendation G.707 [9] as "A
procedure whereby a multiplicity of Virtual Containers is associated
one with another with the result that their combined capacity can be
used as a single container across which bit sequence integrity is
maintained". Two types of concatenation are proposed: contiguous and
virtual.
Contiguous concatenation
Contiguous concatenation uses a concatenation indicator in the
pointer associated with each concatenated frame to indicate that the
SPE/VC with which the pointers are associated are concatenated.
For example, four VC-4s contiguously concatenated in an information
structure would have a data rate of VC-4-4C. The resulting signal
has one valid path overhead (9-byte column) and three 9-byte columns
of fixed stuff. The four payloads are byte interleaved in the VC-4-
4c payload area.
For contiguously concatenated payload to pass through a network, all
intermediate nodes must support contiguous concatenation.
Virtual Concatenation
Many installed network elements in SONET/SDH networks cannot support
contiguous concatenation. The processing in these NEs is limited to
processing only individual SPE/VC. To implement contiguous
concatenation in such networks would require extensive hardware
upgrade of the equipment and would be prohibitively expensive.
Virtual Concatenation is one way of overcoming this problem. The
main aim of virtual concatenation is to provide the SONET/SDH NEs at
both ends of the signal path with the capability of
sending/receiving individual SPE/VC that are associated in a
concatenated group. In this way the cost of transporting
concatenated signal is confined to the up-grade costs at the ends of
the path. These cost are likely to be significantly lower than up-
grading a whole network to handle contiguously concatenated signals.
At the sending end it will be necessary to provide each SPE/VC with
information about its concatenated group identity and its
position/sequence within the group, and to give each its own POH for
Jones Expires June 2000 7
Internet Draft POS with VC, HO & LO December 1999
processing in the intermediate nodes in the network. At the
receiving end the equipment must be capable of identifying a SPE/VC
as belonging to a particular concatenated group and identifying its
position/sequence within that group. Because of the likelihood of
different propagation and processing delays for each of the
individual SPE/VC, it will be necessary for the receiving end
equipment to provide buffers to store the incoming data until the
latest SPE/VC arrives, when re-alignment can be performed.
One method of providing group identification is to use the J1 byte
(Path Trace). If each concatenated group used a different path trace
identifier then the receiving equipment will know that a particular
VC belongs to that group.
The information of what sequence/position a SPE/VC has within the
group must be conveyed in the POH. The receiving end will process
this information and re-assemble the SPE/VC in the correct order.
The difference in the arrival times at the receiver of given
SPEs/VCs in a virtually concatenated group is known as the
Differential Delay. It will be necessary for the receiving equipment
to measure this parameter and to detect if it has gone beyond the
range of the buffers, which have been provided to re-align the
incoming data.
Network Management of the virtually concatenated signal will not
require the network equipment to be modified since the NEs are
processing essentially standard SPE/VC.
5. Emerging Benefits
The main objective of virtual concatenation is to provide multiple
right sized channels over a SONET/SDH network.
The benefit of virtual concatenation to PPP is the ability to
provide channels in a SONET/SDH network that are more appropriate
for IP. The advantages of these channels are bandwidth granularity,
right sized capacity, efficient mapping into SONET/SDH SPE/VC,
traffic scalability and channelized high capacity SONET/SDH
interfaces.
The characteristics of virtually concatenated links, which provide
for bandwidth reduction in the event of a path failure, are a good
match for Differentiated Services. The reason for this is that the
loss of bandwidth will effect the lower priority traffic first and
should allow the higher priority traffic to continue passing over
the link.
Another benefit of virtual concatenation is the ability to add or
remove a SPE/VC from the group without taking a PPP link using the
group Out Of Service. The change in bandwidth should take place in a
few milli-seconds, depending on the physical distance between the
two ends of the link.
Jones Expires June 2000 8
Internet Draft POS with VC, HO & LO December 1999
Virtual concatenation could make better use of SONET/SDH path
protection bandwidth. Consider a single path protected 45Mbit/s or
34Mbit/s circuit. The SONET/SDH bandwidth needed to support this
would involve using two STS-1/VC-3s. When virtual concatenation is
applied to this situation, a link of 100Mbit/s can be provided. In
the event of a path failure this would be reduced to 50Mbit/s.
6. Standards Status
The ITU-T SG13 and SG15 are developing global standards for SDH High
Order and Low Order payload Virtual Concatenation. These changes
will appear in the following standards:
G.803 Architecture of transport networks based on the
synchronous digital hierarchy (SDH)
G.707 Network Node Interface for the Synchronous Digital
Hierarchy (SDH)
G.783 Characteristics of Synchronous Digital Hierarchy (SDH)
Equipment Functional Blocks
Work is proceeding in ITU-T, ANSI T1X1 and ETSI TM1/WP3 to ensure
global standards alignment.
Following the completion of a standard for SONET/SDH SPE/VC virtual
concatenation, it will then become appropriate to consider the use
of this standard for PPP.
7. Security Considerations
This document is for information only. Any protocol related
documents that arise from it would contain security consideration.
8. References
[1] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", RFC
1661, Daydreamer, July 1994.
[2] Simpson, W., Editor, "PPP in HDLC-like Framing, "RFC 1662,
Daydreamer, July 1994.
[3] Malis, A. & Simpson, W., "PPP over SONET/SDH, "RFC 2615, June
1999.
[4] K. Thompson, G. Miller, and R. Wilder, "Wide Area Internet
Traffic Patterns and Characteristics" IEEE Network, Nov 1997.
http://www.vbns.net/presentations/papers/MCItraffic.ps
Jones Expires June 2000 9
Internet Draft POS with VC, HO & LO December 1999
[5] K Claffy, Greg Miller, and Kevin Thompson, "The nature of the
beast: Recent traffic measurements from an Internet backbone",
INET'98 Conference, April 1998.
http://www.caida.org/Papers/Inet98/index.html
[6] Bellcore Publication GR-253-Core "Synchronous Optical Network
(SONET) Transport Systems: Common Generic Criteria" January 1999
[7] American National Standards Institute, "Synchronous Optical
Network (SONET) - Basic Description including Multiplex Structure,
Rates and Formats" ANSI T1.105-1995
[8] American National Standards Institute, "Synchronous Optical
Network (SONET) - Payload Mappings" ANSI T1.105.02-1998
[9] ITU-T Recommendation G.707 "Network Node Interface for the
Synchronous Digital Hierarchy" 1996
[10] Sklower, K. et al., "The PPP Multilink Protocol (MP)" RFC
1990, August 1996
[11] Inverse Multiplexing for ATM (IMA) Specification version 1.1
af-phy-0086.001, March 1999
9. Acknowledgments
Huub van Helvoort, Maarten Vissers(Lucent), Paul Langner (Lucent
Microelectronics), Trevor Wilson (Nortel), Mark Carson (Nortel) and
James McKee (Nortel) for their contribution to the development of
virtual concatenation of SONET/SDH payloads.
Jones Expires June 2000 10
Internet Draft POS with VC, HO & LO December 1999
10. Author's Addresses
Nevin Jones
Lucent Technologies Microelectronics Group
555 Union Boulevard
Allentwon, PA 18103 USA
Email: nrjones@lucent.com
Chris Murton
Nortel Networks Harlow Laboratories
London Road, Harlow,
Essex, CM17 9NA UK
Email: murton@nortelnetworks.com
11. Copyright Notice
Copyright (C) The Internet Society 1999. 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
and distributed, in whole or in part, without restriction of any
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 organisations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Jones Expires June 2000 11
Datatracker
Report a datatracker bug
draft-ietf-pppext-posvcholo-01
Internet-Draft
| Document | Document type |
This is an older version of an Internet-Draft that was ultimately published as RFC 3255.
Expired & archived
|
|
|---|---|---|---|
| Select version | |||
| Compare versions | |||
| Author | |||
| RFC stream |
|
||
| Other formats | |||
| Additional resources | Mailing list discussion |