Hi Kathleen and Matthew,
Thank you for your review and comments. I have updated the draft according to
most of your comments. I don't think it is right to talk about VCCV or
complicated OAM mechanism in current draft. Probably there could be a new draft
talking about this in the future. As for details about configuration parameters
via OMCI, ITU-T is the right and better place to define and reference. ITU-T
G.988 has all the details.
To all,
Besides, I made another two modification.
a) Modify all GPON to G-PON, according latest ITU-T G.987
b) Add XG-PON support. From MPLS PW or IETF point of view, XG-PON is exactly
the same as G-PON, even though they have XGEM. In current draft, all "G-PON"
related terminology could be simply add a "X" prefix and apply to XG-PON system
directly. So, we would not need another draft for XG-PON.
Cheers,
Hongyu
-----Original Message-----
From: [email protected] [mailto:[email protected]]
Sent: Monday, June 27, 2011 9:09 PM
To: [email protected]; [email protected]; [email protected]
Cc: Lihongyu(Hongyu); Robin Zheng(Ruobin); [email protected]
Subject: GEN-ART review for draft-li-pwe3-ms-pw-pon-03
I am the assigned Gen-ART reviewer for this draft. For background on
Gen-ART, please see the FAQ at
< http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>.
Please wait for direction from your document shepherd
or AD before posting a new version of the draft.
Document: draft-li-pwe3-ms-pw-pon-03
Reviewer: Kathleen Moriarty
Review Date: June 27, 2011
IETF LC End Date:
IESG Telechat date: June 28, 2011
Summary: This document is ready with nits.
Major issues:
Minor issues:
Nits/editorial comments:
The acronym PW is used in the abstract and is not defined until the
introduction. Please fix.
Paragraph 7 of the introduction, last sentence:
Change from "Besides coding and
maintenance of these new protocols, a much powerful CPU and more
memory are also necessary for them to run smoothly."
To: "Besides coding and
maintenance of these new protocols, a much more powerful CPU and more
memory are also necessary for them to run smoothly."
If you do not want to repeat the word more, consider the word additional to
replace the second instance of more.
Last paragraph of Section 4:
Consider changing from: "OMCI supports the configuration of a number of PW
types including
TDM, ATM, and Ethernet, and the protocol can also be used to allow
the ONU to notify the OLT of the status of the AC."
To: "OMCI supports the configuration of a number of PW types including
TDM, ATM, and Ethernet. The protocol can also be used to allow
the ONU to notify the OLT of the status of the AC."
pwe3 Working Group H. Li
Internet-Draft R. Zheng
Intended status: Informational Huawei Technologies
Expires: January 7, 2012 A. Farrel
Old Dog Consulting
July 6, 2011
Multisegment Pseudowires in Passive Optical Networks
draft-li-pwe3-ms-pw-pon-04
Abstract
This document describes the application of MPLS multi-segment
pseudowires (MS-PWs) in a dual-technology environment comprising a
Passive Optical Network (PON) and an MPLS Packet Switched Network
(PSN).
PON technology may be used in mobile backhaul networks to support the
end segments closest to the aggregation devices. In these cases,
there may be a very large number of Pseudowire (PW) Terminating
Provider Edge nodes (T-PEs). The MPLS control plane could be used to
provision these end segments, but support for the necessary protocols
would complicate the management of the T-PEs and would significantly
increase their expense. Alternatively, static, or management plane,
configuration could be used to configure the end segments, but the
very large number of such segments in a PON places a very heavy
burden on the network manager.
This document describes how to set up the end segment of an end-to-
end MPLS PW over a Gigabit-capable Passive Optical Network (G-PON) or
10 Gigabit-capable Passive Optical Network (XG-PON) using the G-PON
and XG-PON management protocol, Optical Network Termination
Management and Control Interface (OMCI). This simplifies and speeds
up PW provisioning compared with manual configuration.
This document also shows how a MS-PW may be constructed from an end
segment supported over a PON, and switched to one or more segments
supported over an MPLS PSN.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Li, et al. Expires January 7, 2012 [Page 1]
Internet-Draft MS-PW-PON July 2011
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 7, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology for G-PON/XG-PON . . . . . . . . . . . . . . . . . 6
3. Multi-Segment Pseudowire over PON Network Reference Model . . 7
4. Label Provisioning for Pseudowires over PON . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
The use of PWs in Packet Switched Networks (PSNs) is defined in
[RFC3985]. This architecture is extended in [RFC5659] for multi-
segment pseudowires (MS-PWs) satisfying the requirements in
[RFC5254]. More detail on MS-PWs is provided in [RFC6073].
A MS-PW is a useful technology for certain applications where there
is an aggregation of paths toward a common point in the network, e.g.
mobile backhaul; the segments can be aggregated within tunnels
between PW switching points thus improving scalability and reducing
the number of control plane adjacencies where a control plane is
used.
Segments of a MS-PW in a PSN can be setup using manual provisioning
(static PWs) or using a dynamic control plane such as the Label
Distribution Protocol (LDP)[RFC5036] [RFC4447].
In many scenarios in access and metro networks, Passive Optical
Network (PON) provides longer distance, higher bandwidth with better
economy than other technologies like point-to-point Ethernet or
Digital Subscriber Line (DSL). Mobile backhaul with PON is already
being deployed.
Figure A depicts the physical infrastructure of an Optical
Distribution Network (ODN).
| |
|<--Optical Distribution Network-->|
| |
| branch main |
+-----+ fibers fiber
Base ------| | | |
Stations ------| ONU |\ | |
------| | \ V |
+-----+ \ |
\ +----------+ |
+-----+ \| | | +-----+
Base ------| | | Optical | V | |
Stations ------| ONU |---------| Splitter |-------------| OLT |
------| | /| | | |
+-----+ / +----------+ +-----+
/
+-----+ /
Base ------| |/
Stations ------| ONU |
------| |
+-----+
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Figure A: Typical PON System Architecture
In a PON, the Optical Network Unit (ONU) and Optical Line Termination
(OLT) are adjacent nodes connected by an Optical Distribution Network
(ODN), which consists of optical fibers and optical splitters in a
tree topology. The link between each ONU and OLT is simulated as a
point-to-point link, and there is no path redundancy between them.
The OLT resides in the central office, while ONUs reside in customer
premises. ONUs are deployed in huge numbers and so they are cost
sensitive. More information about ODNs can be found in [G.984.1].
In a mobile backhaul network, many 2G and 3G base stations still use
legacy interfaces like TDM and ATM. Therefore, these native services
must be carried across the PON before they can be carried over the
PSN using PWs. This document describes how MS-PWs can be constructed
with end segments that operate over the PON and are switched to
further segments operated over the PSN. In this case, the base
stations are connected by access circuits (ACs) to the ONUs which act
as Terminating Provider Edge nodes (T-PEs). The OLT is a Switching
Provider Edge (S-PE). This model is shown in Figure B.
Routing protocols and dynamic label distribution protocols like LDP
would significantly increase the ONUs' cost and complexity as they
place requirements on both hardware and software. Besides coding and
maintenance of these new protocols, a much more powerful CPU and more
memory are also necessary for them to run smoothly.
As there is no redundant path between each ONU and the OLT, routing
and path selection are not necessary in the PON. Therefore, static
provision of PWs labels between ONUs and the OLT is simple, and is
preferred because it can greatly reduce the cost of an ONU that acts
as a T-PE. However, use of a Network Management System (NMS) to
provision PWs in a PON would require the network manager to configure
each ONU, and to configure the OLT once for each PW. Since there may
be very many ONUs (and hence very many PWs) in a PON, this requires a
large amount of operational effort. Additionally, there is an issue
that the configuration of each PW at the OLT and ONU might be
inconsistent since these nodes are configured separately. .
[G.988] defines the G-PON/XG-PON management protocol called the ONT
Management and Control Interface (OMCI). OMCI is an implementation
requirement for all G-PON/XG-PON systems. If OMCI is used to
configure PWs on an ONU, no upgrade to an ONU's hardware is required
and the extension to the OMCI implementation is negligible. This
provides a way of reducing the cost and complexity of provisioning
PWs in a G-PON/XG-PON.
This document shows how the two technologies (PON and PSN) can be
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combined to provide an end-to-end multi-segment MPLS PW. The MPLS
PWs are also carried over the PON in MPLS LSP tunnels. There is an
MPLS LSP tunnel each direction between each ONU and the OLT in a one-
to-one relationship with the underlying G-PON/XG-PON channel. The
OLT and ONU perform penultimate hop popping (PHP) [RFC3031] on this
single-hop LSP so no labels are used on the wire for the MPLS LSP
tunnel. There is no change to the operation of MPLS PWs, and MPLS
packets are carried by the G-PON link layer according to ITU-T
[G.984.3amd1] or XG-PON link layer according to ITU-T [G.987.3].
2. Terminology for G-PON/XG-PON
We defined the following terms derived from [G.987]:
o Gigabit-capable Passive Optical Network (G-PON). A variant of the
Passive Optical Network (PON) access technology supporting
transmission rates in excess of 1Gbps and based on the ITU-T
G.984.x series of Recommendations [G.984].
o G-PON Encapsulation Method (GEM). A data frame transport scheme
used in G-PON systems that is connection-oriented and that
supports fragmentation of the user data frames into variable sized
transmission fragments.
o GEM Port. An abstraction of the G-PON adaptation layer
representing a logical connection associated with a specific
client packet flow between the OLT and the ONU.
o 10-gigabit-capable passive optical network (XG-PON): A PON system
supporting nominal transmission rates on the order of 10 Gbit/s in
at least one direction, and implementing the suite of protocols
specified in the ITU-T G.987.x series Recommendations.
o XG-PON encapsulation method (XGEM): A data frame transport scheme
used in XG PON systems that is connection-oriented and that
supports fragmentation of user data frames into variable sized
transmission fragments.
o XGEM port: An abstraction in the XGTC service adaptation sublayer
representing a logical connection associated with a specific
client packet flow.
o Optical Distribution network (ODN). In the PON context, a tree of
optical fibers in the access network, supplemented with power or
wavelength splitters, filters, or other passive optical devices.
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o Optical Line Termination (OLT). A device that terminates the
common (root) endpoint of an ODN, implements a PON protocol, such
as that defined by ITU-T G.984 series, and adapts PON PDUs for
uplink communications over the provider service interface. The
OLT provides management and maintenance functions for the
subtended ODN and ONUs. In this document, the OLT is a network
element with multiple PON ports and uplinks that provide switching
capability to the PSN.
o Optical Network Termination (ONT). A single subscriber device
that terminates any one of the distributed (leaf) endpoints of an
ODN, implements a PON protocol, and adapts PON PDUs to subscriber
service interfaces. An ONT is a special case of an ONU.
o Optical Network Unit (ONU). A generic term denoting a device that
terminates any one of the distributed (leaf) endpoints of an ODN,
implements a PON protocol, and adapts PON PDUs to subscriber
service interfaces. In some contexts, an ONU implies a multiple
subscriber device. In this document, an ONU is a Provider Edge
(PE) node with one or more ACs that map to the service interfaces.
The ONU acts as a T-PE.
o ONT Management and Control Interface (OMCI). The management and
control channel between OLT and ONT in PON. The OMCI protocol
runs between the OLT Controller and the ONT Controller across a
GEM connection that is established at ONT initialization. The
OMCI protocol is asymmetric: the Controller in the OLT is the
master and the one in the ONT is the slave. A single OLT
Controller using multiple instances of the protocol over separate
control channels may control multiple ONTs. The OMCI protocol is
used to manage the ONT in areas of configuration, fault
management, performance and security.
o Passive Optical Network (PON). An OLT connected using an ODN to
one or more ONUs or ONTs.
3. Multi-Segment Pseudowire over PON Network Reference Model
[RFC5659] provides several pseudowire emulation edge-to-edge (PWE3)
reference architectures for the multi-segment case. These are
general models extended from [RFC3985] to enable point-to-point
pseudowires through multiple PSN tunnels.
A G-PON/XGPON consists of an OLT, an ODN and multiple ONUs. The ODN
is actually a fiber tree that provides physical connections between
the OLT and the ONUs. G-PON/XG-PON has its own physical layer and
link layer. A GEM/XGEM Port is a logical point-to-point connection
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between the OLT and each ONU over GPON Transmission Convergence (GTC)
layer/XG-PON transmission convergence (XGTC) layer. There can be
more than one GEM/XGEM port between the OLT and an individual ONU.
Each GEM/XGEM port can be assigned different QoS and bandwidth.
Figure B shows how the MS-PW architecture is applied to a network
comprising a PON and a PSN. The Terminating PE1 (TPE1) is an ONU and
the Switching PE1 (SPE1) is an OLT. One or more PWs runs between the
ONU and the remote end system (TPE2) to provide service emulation
between CEs (CE1 and CE2).
In each of the PON and PSN, the PW segments are carried in PSN
tunnels. In the PSN, the tunnel is established and operated as
normal for PWs (see [RFC3985]). In the PON, the tunnel used is a
single-hop MPLS LSP tunnel so that the OLT and ONU are label edge
routers. The OLT and ONU make use of PHP on the MPLS LSP tunnel and,
since this is a single hop LSP (there are no MPLS-capable nodes
between the OLT and ONU) this means that there is no MPLS
encapsulation for the MPLS LSP tunnel on the wire (that is, no label
or shim header is used). This results in the on-wire encapsulations
shown in Figure C.
Native |<------Multi-Segment Pseudowire------>| Native
Service | GEM/XGEM | Service
(AC) | |<--Port-->| | (AC)
| | | | | |
| | | PSN | PSN | |
| | |<-Tunnel->| |<-Tunnel->| | |
| V V V V V V |
| +----+ +-----+ +----+ |
+----+ | |TPE1|===========|S-PE1|==========|TPE2| | +----+
| |------|..... PW.Seg't1....X....PW.Seg't3.....|-------| |
| CE1| | | | | | | | | |CE2 |
| |------|..... PW.Seg't2....X....PW.Seg't4.....|-------| |
+----+ | | |===========| |==========| | | +----+
Base ^ +----+ +-----+ +----+ ^
Station | Provider Edge 1 ^ Provider Edge 2 |
| ONU | |
| PW switching point |
| OLT |
| |
|<------------------ Emulated Service --------------->|
Figure B: MS-PW over PON Network Reference Model
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Base ----AC-- TPE1--PW over PON--SPE1--PW over PSN--TPE2--AC------
Station
---------- ----------
-------- |Packetized| |Packetized| --------
|Native | |Native | |Native | |Native |
|Service | |Service | |Service | |Service |
-------- |----------| |----------| --------
|Control | |Control |
|Word | |Word |
|----------| |----------|
|PW Label | |PW Label |
|----------| |----------|
|GEM/XGEM | |MPLS |
|----------| |Tunnel |
|GPON/XGPON| |Label |
|-Phy | | |
---------- |----------|
|Link Layer|
|----------|
|Phy |
----------
Figure C: On-Wire Data Encapsulations for MS-PWs
It should be noted that all PW segments are of the same technology,
which is packet encapsulated.
The use of the PW label enables multiple PWs to multiplexed over a
single GEM/XGEM port within the MPLS LSP tunnel. This enables the
traffic for multiple base stations to be kept separate, and allows
different services and separate ACs for a single base station to be
supported. Furthermore, the multiple ACs at an ONU can belong to
different native services.
At the same time, each ONU can support more than one GEM/XGEM port
(each supporting a single MPLS LSP tunnel) connecting it to the OLT.
This allows greater bandwidth and so more PWs. It may also be used
to provide a simple way to aggregate PWs intended to be routed across
different PSN tunnels in the core network, or even across different
core networks.
At present, Ethernet over GEM/XGEM is the dominant encapsulation in
G-PON/XG-PON. For fast deployment of MPLS over G-PON/XG-PON, putting
MPLS PWs over Ethernet over GEM/XGEM is an alternative way of
transporting MPLS PWs over G-PON/XG-PON with existing hardware.
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4. Label Provisioning for Pseudowires over PON
For a MS-PW with a segment running over a PON, where the OLT acts as
a S-PE and the ONU as a T-PE, PW provisioning can be performed
through static configuration, e.g., from an NMS. However, in this
model, each ONU has to be configured as each PW is set up. The huge
number of ONUs (and PWs) makes this method quite forbidding.
The labor of provisioning static labels at the ONUs for PWs can be
significantly reduced by using a management protocol over PON. This
approach keeps the ONU simple by not requiring the implementation of
a new dynamic control protocol.
The usual management protocol in a G-PON/XG-PON system used to manage
and control ONUs is OMCI. It is used to perform all G-PON/XG-PON
physical layer and data GTC/XGTC layer configuration on ONUs. Per
[G.984.4amd2] and [G.988], OMCI can also be used to set up PWs and
the MPLS LSP Tunnels from ONUs to OLT. When using OMCI to provision
PWs in a G-PON/XG-PON, the network manager sends configuration
information to the OLT only. The OLT will select suitable PW labels
and send all PW and MPLS LSP tunnel parameters to the ONUs through
OMCI. The AC can be identified in the OMCI signaling so that the
network manager does not need to configure the PWs at each ONU.
OMCI supports the configuration of a number of PW types including
TDM, ATM, and Ethernet. The protocol can also be used to allow the
ONU to notify the OLT of the status of the AC.
5. IANA Considerations
This document makes no request for IANA action.
6. Security Considerations
G-PON/XG-PON has its own security mechanism to guarantee each ONU is
isolated on the G-PON/XG-PON link layer. Other security issues are
unchanged from those applying as standard to PWs and MS-PWs. Please
refer to the referenced architectures and protocol specifications for
further details.
7. References
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7.1. Normative References
[G.984.1] ITU-T, "Gigabit-capable passive optical networks (GPON):
General characteristics", March 2008,
<http://www.itu.int/rec/T-REC-G.984.1-200803-I>.
[G.984.3amd1]
ITU-T, "Gigabit-capable Passive Optical Networks (G-PON):
Transmission convergence layer specification",
February 2009,
<http://www.itu.int/rec/T-REC-G.984.3-200902-I!Amd1>.
[G.987] "10-Gigabit-capable passive optical network (XG-PON)
systems: Definitions, abbreviations, and acronyms",
October 2010,
<http://www.itu.int/rec/T-REC-G.987-201010-I>.
[G.987.3] "10-Gigabit-capable passive optical networks (XG-PON):
Transmission convergence (TC) specifications",
October 2010,
<http://www.itu.int/rec/T-REC-G.987.3-201010-P>.
[G.988] ITU-T, "ONU management and control interface (OMCI)
specification", 2010.
[RFC3031] "Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.".
[RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-
Edge (PWE3) Architecture", March 2005.
[RFC4447] "Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G.
Heron, "Pseudowire Setup and Maintenance Using the Label
Distribution Protocol (LDP)", RFC 4447, April 2006.".
[RFC5036] "Andersson, L., Minei, I., and B. Thomas, "LDP
Specification", RFC 5036, October 2007.".
[RFC5254] Bitar, N., Bocci, M., and L. Martini, "Requirements for
Multi-Segment Pseudowire Emulation Edge-to-Edge (PWE3)",
October 2008.
[RFC5659] Bocci, M. and S. Bryant, "An Architecture for Multi-
Segment Pseudowire Emulation Edge-to-Edge", October 2009.
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7.2. Informative References
[G.984.4amd2]
ITU-T, "Gigabit-capable passive optical networks (G-PON):
ONT management and control interface specification",
November 2009,
<http://www.itu.int/rec/T-REC-G.984.4-200911-I!Amd2>.
[RFC6073] Martini, L., Metz, C., Nadeau, T., Bocci, M., and M.
Aissaoui , "Segmented Pseudowire", January 2011.
Authors' Addresses
Hongyu Li
Huawei Technologies
Huawei Industrial Base
Shenzhen
China
Email: [email protected]
Ruobin Zheng
Huawei Technologies
Huawei Industrial Base
Shenzhen
China
Email: [email protected]
Adrian Farrel
Old Dog Consulting
Email: [email protected]
Li, et al. Expires January 7, 2012 [Page 12]
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