Ethernet Over Transport

8/8/2019 Ethernet Over Transport

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Ethernet over TransportWhite Paper

Document No.: PMC-2050704, Issue 1 1

Ethernet over Transport

Technology White Paper

by Steve Gorshe, Principal Engineer

Issue No. 1: July, 2005

PMC-Sierra, Inc.


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Legal Information

Copyright

Copyright 2005 PMC-Sierra, Inc. All rights reserved.

The information in this document is proprietary and confidential to PMC-Sierra, Inc., and for its

customers internal use. In any event, no part of this document may be reproduced or

redistributed in any form without the express written consent of PMC-Sierra, Inc.

PMC-2050704 (01)

Disclaimer

None of the information contained in this document constitutes an express or implied warranty

by PMC-Sierra, Inc. as to the sufficiency, fitness or suitability for a particular purpose of any

such information or the fitness, or suitability for a particular purpose, merchantability,

performance, compatibility with other parts or systems, of any of the products of PMC-Sierra,

Inc., or any portion thereof, referred to in this document. PMC-Sierra, Inc. expressly disclaims

all representations and warranties of any kind regarding the contents or use of the information,

including, but not limited to, express and implied warranties of accuracy, completeness,

merchantability, fitness for a particular use, or non-infringement.

In no event will PMC-Sierra, Inc. be liable for any direct, indirect, special, incidental or

consequential damages, including, but not limited to, lost profits, lost business or lost data

resulting from any use of or reliance upon the information, whether or not PMC-Sierra, Inc. hasbeen advised of the possibility of such damage.

Trademarks

For a complete list of PMC-Sierras trademarks and registered trademarks, visit:

http://www.pmc-sierra.com/legal/

Patents

Relevant patent grants may exist.
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Abstract

A convergence of technology and applications has created an increased desire for Ethernet

WAN connectivity. In many ways, Ethernet is an obvious technology choice. It simplifiesenterprise network administration, and provides a ubiquitous, inexpensive infrastructure of

existing Ethernet interfaces on enterprise equipment. The development of VCAT and GFPallows efficient transport of Ethernet frames through SONET/SDH networks. In addition,

Ethernet bridge and router technology requires less provisioning and administration than

technologies such as ATM. As some carriers begin a migration to using packet switching

technology such as MPLS in their core networks rather than traditional circuit switching,

Ethernet again looks like an excellent fit as an access technology.

This white paper describes how standards are developing to provide Ethernet WAN

connectivity and primarily focuses on the set of new standards for Ethernet transport over public

networks developed by ITU-T Study Group 15 (SG15). It discusses the Ethernet services that

are being considered over public WANs; transport network models that can be used to supportEthernet services; the Ethernet-based user network interfaces (UNIs) and network-to-network

interfaces (NNIs) required for transport network equipment to carry Ethernet services;

Operations and Maintenance (OAM) capabilities; and protection and restoration technologies

that can be used to guarantee carrier-grade service reliability for Ethernet WAN services.

About PMC-Sierra

PMC-Sierra is a leading provider of high-speed broadband communications and storage

semiconductors and MIPS-Poweredprocessors for Enterprise, Access, Metro Optical

Transport, Storage Area Networking and Wireless network equipment. The company offers

worldwide technical and sales support, including a network of offices throughout NorthAmerica, Europe and Asia. The company is publicly traded on the NASDAQ Stock Market

under the PMCS symbol and is included in the S&P 500 Index.

About the Author

Steve Gorshe, Ph.D. is a Principal Engineer in the Product Research Group and oversees ICs for

SONET, optical transmission and access systems.

Currently, Steve is a senior member of the IEEE and co-editor for the IEEE Communications

magazines Broadband Access Series. He is the chief editor for the ATIS OPTXS Committee

(formerly T1X1), which is responsible for SONET and optical network interface standards. Heis a recent recipient of the Committee T1 Alvin Lai Outstanding Achievement Award for his

standards work and has been a technical editor for T1.105, T1.105.01, T1.105.02, and T1.105.07

within the SONET standard series as well as the ITU-T G.7041, G.8011.1, G.7043, and G.8040

recommendations. He has 26 patents issued or pending and several published papers.


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Table of Contents

Legal Information...........................................................................................................................2

Copyright................................................................................................................................. 2Disclaimer ...............................................................................................................................2

Trademarks............................................................................................................................. 2

Patents.................................................................................................................................... 2

Abstract .........................................................................................................................................3

About PMC-Sierra................................................................................................................... 3

About the Author ..................................................................................................................... 3

Revision History ......................................................................................................................4

1 Preface .................................................................................................................................... 8

2 Why Ethernet Over the Public WAN? ..................................................................................... 9

3 Service Types and Characteristics........................................................................................ 12

3.1 Ethernet Connection (EC) Defined ............................................................................. 12

3.2 Ethernet Connection (EC) Attributes........................................................................... 15

3.2.1 Network Connectivity ..................................................................................15

3.2.2 Transfer Characteristics.............................................................................. 17

3.2.3 Separation (Customer and Service Instance)............................................. 18

3.2.4 Link Type.....................................................................................................18

3.2.5 Connectivity Monitoring...............................................................................18

3.2.6 Bandwidth Profile ........................................................................................ 18

3.2.7 UNI List ....................................................................................................... 18

3.2.8 Preservation................................................................................................ 19

3.2.9 Survivability................................................................................................. 19

3.3 Ethernet Private Line (EPL) Service ........................................................................... 19

3.4 Ethernet Virtual Private Line (EVPL) Service.............................................................. 21

3.5 Ethernet Private LAN (EPLAN) Service ...................................................................... 22

3.6 Ethernet Virtual Private LAN (EVPLAN) Service ........................................................24

4 Ethernet Client Interfaces .....................................................................................................254.1 Multiplexed Access......................................................................................................25

4.2 VLAN Mapping ............................................................................................................ 26

4.3 Bundling ...................................................................................................................... 27

4.4 Bandwidth Profile ........................................................................................................ 27

4.5 Layer 2 Control Protocol Processing ..........................................................................27


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4.6 Summary of UNI Service Attributes for Different Services.......................................... 27

5 Protection and Restoration ................................................................................................... 29

5.1 Service Protection or Restoration Provided by the Transport Network ...................... 29

5.2 Service Restoration at Layer 2.................................................................................... 30

6 Conclusion ............................................................................................................................ 31

A Related Standards Activity .................................................................................................... 32

B Definitions ............................................................................................................................. 34

C References............................................................................................................................ 35


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List of Figures

Figure 1 Illustration of Ethernet Service Areas (ITU-T Rec. G.8011)........................................ 13

Figure 2 Illustration of Private and Virtual Private Connections................................................14Figure 3 Network Connectivity Examples..................................................................................16

Figure 4 Network Portion of the Multipoint-to-Multipoint Topology (ITU-T Rec.G.8011) .................................................................................................................... 17

Figure 5 EPL Service Illustration ............................................................................................... 19

Figure 6 EPLAN Illustrations .....................................................................................................22

Figure 7 Service Multiplexing Example ..................................................................................... 26

List of Tables

Table 1 Summary of the Types of Ethernet Services................................................................ 14

Table 2 Ethernet Connection Service Attributes (Derived from ITU-T Rec.G.8011) .................................................................................................................... 15

Table 3 EPL Connection Characteristics (Derived from ITU-T Rec. G.8011.1)........................ 20

Table 4 EVPL Connection Characteristics ................................................................................ 21

Table 5 EPLAN Expected Connection Characteristics ............................................................. 23

Table 6 EVPLAN Expected Connection Characteristics........................................................... 24

Table 7 UNI Service Attributes Common to All Services .......................................................... 25Table 8 Service-dependent UNI Service Attributes................................................................... 25

Table 9 Summary of UNI Service Attributes for EPL and EVPL Services ................................ 28

Table 10 Summary of Related Standards Activities.................................................................. 32


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1 Preface

Due to a convergence of business requirements for higher data connectivity rates and flexible

services, and the availability of new data transport technology, Ethernet has become thetechnology of choice for WAN connectivity both from the perspective of the enterprise and

from the perspective of the carrier (network operator).

This white paper examines the popularity of Ethernet over Transport and what factors

enterprises and carriers need to consider. Included in the discussion is an overview of Ethernet

services that are being considered for delivery over public WANs as well as the attributes and

characteristics that must be defined in order to provide these services. This discussion is based

on the Ethernet transport work done for the ITU-T Study Group 15 (SG15) and its series of new

standards. (See Appendix A.)

This paper also examines the Ethernet-based user network interfaces (UNIs) and network-to-

network interfaces (NNIs) that are required for transport network equipment carrying Ethernetservices as well as Operations, Administration and Maintenance (OAM) capabilities. (Some

OAM capability is already available in Ethernet services deployed over SONET/SDH (server

networks), but additional capabilities are required at the Ethernet Client layer.) The paper

concludes with a summary of some of the protection and restoration technologies that can be

used to guarantee carrier-grade service reliability for Ethernet WAN services.


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2 Why Ethernet Over the Public WAN?

On the enterprise side of the public WAN, Ethernet is the dominant technology. There are many

reasons why there is growing interest in Ethernet WAN connection services:

At the enterprise, where it is the dominant technology, network administrators are already

familiar and comfortable with Ethernet.

A number of applications, including voice and video, are already being encapsulated into

Ethernet and run over enterprise network LANs.

More and more companies have a number of remote offices that need to exchange data with

the headquarters office or with each other. There can be significant advantages to placing

data on common servers that can be accessed by all sites.

The increased importance of the Internet for business applications has led to an increasing

desire for incrementally higher WAN interface rates.

It is desirable to have a single Internet firewall at one site that is accessed on the enterprise

network by all sites.

Most enterprise WAN data access today uses Frame Relay connections at rates of fractional

DS1, full-rate DS1, fractional DS3, and full-rate DS3. In some cases, the data services use ATM

instead of Frame Relay either for the customer connection or as a method of transporting the

data through the core network. Frame Relay-based services suffer from a lack of scalability in

terms of both high-speed connections and ubiquitous multipoint networks. ATM suffers from

being somewhat provisioning-intensive in large networks and bandwidth inefficient.

At the other end of the spectrum, some customers use WDM or dark fiber for their WAN or

MAN connections with native Gigabit Ethernet, 10 Gbit Ethernet, or Fibre Channel. However,

WDM equipment is expensive and not ubiquitously deployed, and dark fiber is not universally

available, which limits the applications for these approaches. Another drawback of WDM and

dark fiber applications is that unless they use the new G.709 Optical Transport Network

standard [1], there is no embedded overhead for carriers to monitor the quality of the connection

or provide protection switching in order to guarantee their service level agreements (SLAs).

Some larger customers use high-speed SONET OC-N / SDH STM-N connections, which

typically terminate the Ethernet frames and re-encapsulate the data into PPP, and use Packet

over SONET/SDH (PoS) for transmission through a SONET/SDH pipe. On the carrier (network

operator) side, the situation is somewhat complicated. In the wake of the telecom bubble burstin 2000, carriers face two clear drivers. First, they must deploy any new services on their

existing SONET/SDH networks. Throughout the 1990s, carriers invested heavily in building

SONET/SDH-based fiber optic networks, including developing the Operations, Administration,Maintenance and Provisioning (OAM&P) systems to run them. The enormous capital

investment required to build an overlay network for data transport, be it native Ethernet orDWDM-based, makes overlay networks unrealistic. Fortunately, SONET/SDH has proven

flexible enough to handle the challenge.


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Recent developments that extend the useful life of SONET/SDH include:

Virtual concatenation (VCAT) [2][3] to create more flexible data channel sizes.

Link Capacity Adjustment Scheme (LCAS) [4] to increase the flexibility and functionality

of VCAT.

Generic Framing Procedure (GFP) [5][6] to encapsulate data frames for robust and

bandwidth-deterministic transport.

Resilient Packet Ring (RPR) technology that provides a very flexible technology for data

access onto SONET/SDH access and metro rings.

A second driver for carriers is the desire to generate new, revenue-bearing services. With data

traffic continuing to grow faster than voice, offering WAN connectivity with higher bandwidth

and enhanced service capabilities appears to be a natural direction for new services. Equipment

and device manufacturers, who are also interested in building new products, have also seen

WAN connectivity as a natural direction.

Ethernet is in many ways an obvious technology choice for WAN connectivity. The job of

enterprise network administration is simplified if all their sites can be treated as part of the same

Ethernet network. In addition, Ethernet interfaces are relatively inexpensive and are ubiquitous

on enterprise equipment. The development of VCAT and GFP allows efficient transport of

Ethernet frames through SONET/SDH networks. In addition, Ethernet bridge and router

technology requires less provisioning and administration than technologies such as ATM. As

some carriers begin a migration to using packet switching technology such as MPLS in their

core networks rather than traditional circuit switching, Ethernet again looks like an excellent fit

as an access technology.

The IEEE, ITU-T Study Group 15 and 13, Metro Ethernet Forum (MEF), and Internet

Engineering Task Force are working on developing Ethernet transport standards. (Refer toAppendix A.) This level of standards activity is a good indication of how many companies and

organizations are interested in Ethernet WAN.

OAM is critical once Ethernet is extended beyond the customer premise, especially when

multiple transport service providers carry the traffic. In fact, although it is being actively

addressed by multiple standards bodies, including the ITU-T SG13, IEEE, and the MEF,

Ethernet currently lacks some of the OAM capabilities that will be required to monitor and

guarantee service level agreements (SLAs). In a multiple carrier environment, for example,

OAM is crucial for determining the locations of problems and degradations when they occur.

From a transport network provider standpoint, this OAM requirement is an area where

SONET/SDH really shines. The OAM capabilities inherent in the SONET/SDH backbone allow

full monitoring and protection of the transmission facilities and transport path through theSONET/SDH network.


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Note that the relatively low cost of Ethernet enterprise equipment has created a customer

expectation that Ethernet WAN interfaces should be less expensive than DS1/DS3 Frame Relay

interfaces. For the carriers, even if the Ethernet connectivity is provided through their

SONET/SDH backbone network, they still have to develop new OAM&P procedures and tools

to provide the service. Therefore, even though customers and carriers agree that Ethernet (overSONET/SDH for the carriers) is the most attractive technology for high-speed WAN

connectivity, there is an inherent conflict between carriers needing to invest in equipment and

management system upgrades and customers demanding and expecting to pay less for Ethernet-

based services.


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3 Service Types and Characteristics

The description of Ethernet transport services varies depending on ones vantage point. This

white paper approaches Ethernet transport from the perspective of a transport network orservice provider, rather than from a customer view of Ethernet transport services, and follows

the approach of the ITU-T G.8011 recommendation [9] in its discussion of the service types andcharacteristics of Ethernet. (The G.8011.x series covers specific services within the framework

of G.8011.)

One can say that the goal of the network provider is to make Ethernet service look like an

extension of the customers Ethernet LAN. In order to provide this transparency, the network

provider must take into account a number of items that are not necessarily directly visible to the

customer. These items are presented in this section in terms of Ethernet connection attributes

and their associated parameters.

3.1 Ethernet Connection (EC) Defined

An Ethernet Virtual Connection (EVC), otherwise known as an Ethernet Connection (EC),

provides a connection between two or more customer UNIs such that the Ethernet frames

(service frames) associated with the EVC can only be transferred between its associated UNIs

and not to any others. Note that to be consistent with ITU-T G.8011, this white paper uses the

more generic term, EC, rather than EVC.

Figure 1 illustrates an EC with its different reference points from the standpoint of both the

Ethernet MAC layer network (ETH) and Ethernet physical layer network (ETY). Figure 1 also

illustrates the three different Ethernet service areas in a multi-carrier Ethernet connection:

Access (UNI-C to UNI-N)

End-to-end/customer-to-customer (UNI-C to UNI-C)

Edge-to-edge/intra-carrier (UNI-N to UNI-N)


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Figure 1 Illustration of Ethernet Service Areas (ITU-T Rec. G.8011)

Operator FD Operator FD

TransportTransportTransport

OperatorOperatorOperatorBBBsss

NetworkNetworkNetwork

TransportTransportTransport

OperatorOperatorOperatorAAAsss

NetworkNetworkNetwork

UNIAttributes Ethernet ConnectionAttributes

demarc

Customer Customer

UNI-N UNI-NUNI-C UNI-C

FD

ETHETH

demarc

Access AccessUNI-N to UNI-N

UNI-C to UNI-C

NNIAttributes

NNI

FD

ETYETY

Operator FD Operator FD

Notes

1. FD = Flow Domain

2. Diagram reprinted with permission from ITU-T Recommendation G.8011.

From a customers perspective, the EC connectivity can be one of two types:

Line connectivity (point-to-point)

LAN connectivity (point-to-multipoint or multipoint-to-multipoint)

From a transport network viewpoint, these line and LAN connections can either be provided:

Through dedicated transport channels, including router bandwidth (private service)

Through a shared medium (virtual private service)

The difference between a private line connection and a virtual private line connection is

illustrated in Figure 2. The service type variations are summarized in Table 1.


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Figure 2 Illustration of Private and Virtual Private Connections

SONET/SDH/PDH/OTN

Carrier Network

Customer AEquipment

Ethernet

PHY

CarrierEquipment

CarrierEquipment

Customer AEquipment

Ethernet

PHY

Customer BEquipment

Customer BEquipment

SONET/SDH/PDH/OTH

Carrier Network

Customer AEquipment

EthernetPHY

CarrierEquipment

CarrierEquipment

Customer AEquipment

EthernetPHY

Customer BEquipment

Customer BEquipment

a) EPL for two customers, each with their own TDM channel

b) EVPL for two customers where they share a TDM channel for increased

efficiency

Table 1 Summary of the Types of Ethernet Services

Connectivity Resource Sharing Service Type

Dedicated EPL (Ethernet Private Line)Point-to-point

Shared EVPL (Ethernet Virtual Private Line)

Dedicated EPLAN (Ethernet Private LAN)Multipoint

Shared EVPLAN (Ethernet Virtual Private LAN)

Note

1. The Metro Ethernet Forum(MEF) refers to EPL and EVPL as E-Line services, and EPLAN andEVPLAN as E-LAN services.


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3.2 Ethernet Connection (EC) Attributes

Various EC service attributes must be taken into account in a transport or service provider

network. Table 2 lists these attributes.

Table 2 Ethernet Connection Service Attributes (Derived from ITU-T Rec. G.8011)

EC Service Attribute Service Attribute Parameters and Values

Network connectivity Point-to-point, point-to-multipoint, multipoint-to-multipoint

Address (deliver conditionally or unconditionally)

Drop Precedence (drop randomly, drop conditionally, or not applicable)

Transfer characteristics

Class of Service

CustomerSeparation

Service instance

Spatial or logical

Link type Dedicated or shared

Connectivity monitoring Sub-layer monitoring: On demand, proactive, none

Inherent monitoring: Proactive

Bandwidth profile Specified

UNI list An arbitrary text string to uniquely identify the UNIs associated with the EC.

VLAN ID (yes or no)Preservation

Class of Service (yes or no)

Survivability None, or server-specific

3.2.1 Network Connectivity

One way in which Ethernet services can be characterized is by the type of desired customer

connectivity. The types of connectivity are:

Point-to-point

Point-to-multipoint

Multipoint-to-multipoint

Figure 3 shows examples of these different connectivity types. Figure 3 (a) shows a basic point-

to-point connection between customers through a transport network. Figure 3 (b) shows a

popular point-to-multipoint topology known as hub-and-spoke. Figure 3 (c) through (e) show

examples of various multipoint-to-multipoint topologies.

Care must be taken to avoid confusing the customer connectivity (logical topology) with the

physical topology of the underlying network providing that connectivity. For example,

Figure 3 (b) and Figure 3 (d) use the same physical topology. The difference between a hub-

and-spoke and a star network is that a star network provides arbitrary multipoint-to-multipoint

connectivity between all the customer nodes while a hub-and-spoke network connects the hub

customer node to each of the spoke customer nodes (point-to-multipoint). Any connectivity

between spoke nodes would have to be provided by a router at the customers hub node.


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A logical hub-and-spoke network could be provided over the physical topology of any of the

networks in Figure 3 (b) through (e). Figure 3 (c) through (e) illustrate common transport

network topologies. In reality, a transport network will often consist of a combination of star,

ring, and more arbitrary mesh sub-networks.

Figure 3 Network Connectivity Examples

TRANSPORT

NETWORKCE CE

a) Point-to-pointTRANSPORT

NETWORK

CE

CE

CE

CE

CE

b) Hub and spoke

TRANSPORTNETWORK

CE

CE CE

CE

CE

TRANSPORT

NETWORK

CE

CE CE

CE

CE

c) Ring

d) StarTRANSPORT

NETWORKCE

CE CE

CE

CE

e) Arbitrary

CE = Customer Edge

When discussing multipoint-to-multipoint connectivity, it is common to refer to the network

topological componentthat provides the desired forwarding of information between source and

destination UNIs as aflow domain (FD)1. In the example shown in Figure 4, if customers M and

1 A topological component describes a portion of a layer network in terms of the topological relationship

between the (flow) points.


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N are exchanging data, each is connected to a FD, with the flow domains being connected

through an Ethernet link flow (LF) over the ABC network entity.

Figure 4 Network Portion of the Multipoint-to-Multipoint Topology (ITU-T Rec. G.8011)

ETH FD

ETH FD

ETH FD

ETH LF

ETH LF

ETH LF

ABCnetwork entity

PQRnetwork entity

XYZnetwork entity

ETH UNI

ETH UNI

ETH UNI

ABC, PQR, XYZ are server layer networks (can all be the same or different).They may be CO-CS, CO-PS, CLPS

Customer M Customer N

Note

1. Diagram reprinted with permission from ITU-T Recommendation G.8011.

A point-to-point connection can be characterized as either not having a flow domain or as

having a flow domain with only twoflow points (that is, two end points of the networkconnection). The point-to-point connection is typically described as not having a flow domain

since a flow domain implies a layer network with inherent switching/routing and other layer

network capabilities. A flow domain with only two points is really the degenerate case of a

multipoint network and leaves open the potential of adding additional flow points (UNIs) to the

network.

3.2.2 Transfer Characteristics

The transfer characteristics of a network relate to what frames are to be delivered to the

destination unconditionally, delivered conditionally, or are to be dropped. In the case of

Ethernet, the three parameters that determine the disposition of a frame are:

Address

Drop Precedence (DP)

Class of Service (CoS)


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For the address, a frame either can be delivered unconditionally, regardless of its destination

address, or be delivered for only some destination addresses. The DP indicates the relative

priority of the frame if it encounters a congestion situation in which frame dropping must occur.

If dropping is based on the DP, frames are said to be dropped conditionally. Another option

would be dropping randomly (that is, drop the overflow frames from a full queue). For someservices, frames cannot be dropped and hence DP is not applicable. The CoS parameter, which

is based on the DP and indicates the frames class queuing, is not fully defined at this time.

3.2.3 Separation (Customer and Service Instance)

Separation refers to how the traffic of each customer or service instance is kept separate from

the traffic of others. In the case of customer separation, the traffic from different customers is

separated. In the case of service instance separation, the different service instances are

separated, even for the same customer. A spatial separation implies a circuit switched network

(for example, a TDM network in which each customer has its own TDM channel or facility, or a

virtual circuit such as in an ATM network). Logical separation implies that customer or service

instance traffic is separated at the packet level (that is, based on per-packet information such asaddress or tag values).

3.2.4 Link Type

A link can either be dedicated to a single customer service instance or shared among multiple

service instances. For a dedicated link, a single customer service instance has a one-to-one

mapping to a set of one or more Ethernet links and the associated server layer trail (that is, a

spatial separation from other service instances). As such, the service instance does not compete

for bandwidth/resources (transport and switch fabric bandwidth) with other service instances,

and does not allow multiplexing on the access link (see Figure 2(a)). On the other hand, a

shared link allows more than one service instance to share that link, (that is, logical separation)

which means that the service instances can compete for the link resources (see Figure 2(b)).

3.2.5 Connectivity Monitoring

Connectivity monitoring is the mechanism by which network nodes determine their ongoing

connectivity to their neighbor nodes in that layer network.

3.2.6 Bandwidth Profile

A bandwidth profile specifies that parameters that a traffic flow must meet at a UNI or NNI.

Policing of the bandwidth profile is typically done at the edge of the transport network.

3.2.7 UNI List

For the purposes of management and control, a service provider assigns an arbitrary string to

uniquely identify each UNI.


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3.2.8 Preservation

Preservation refers to whether a customers Ethernet frame VLAN ID and/or CoS are preserved

through the transport network. If the value is preserved, it will have the same value at the egress

UNI that it had at the ingress UNI of the transport network. In some circumstances, however, itmay be necessary or desirable to change these values within the transport network. For example,

the service provider may perform a translation between the VLAN ID values that a customer

uses on the customer side of the network to a different set of VLAN IDs that are used within the

service provider network. Another example is that if a frame fails to meet the specified

bandwidth profile, the ingress node may choose to let it pass into the transport network but will

set its DP value to a higher value so that it is prioritized for dropping if it encounters congestion.

3.2.9 Survivability

Survivability pertains to the ability of the network to continue to provide service under

situations in which a fault(s) exists in the network.

3.3 Ethernet Private Line (EPL) Service

EPL, as illustrated in Figure 5 and Figure 2, consists of point-to-point Ethernet connections

using reserved, dedicated bandwidth. With EPL, the transport network effectively looks like a

piece of wire from the Ethernet client perspective. From the transport network provider

standpoint, however, the transport network (server layer) provides the performance monitoring

and protection capabilities required for guaranteeing the service level agreement (SLA) with thecustomer.

Figure 5 EPL Service Illustration

SONET/SDH/PDH/OTH(or ATM/MPLS CIR)

Carrier NetworkCustomerEquipment

EthernetPHY

CarrierEquipment

CarrierEquipment

CustomerEquipment

EthernetPHY

The primary advantages of EPL are the simplicity of setting up a dedicated circuit, and the

security for the traffic that is inherent when it is isolated in its own TDM channel2. Sharing

bandwidth can lead to greater bandwidth efficiency in the transport network due to statistical

multiplexing gains, however it is more difficult to administer since it requires additional effort(for example, traffic engineering and monitoring) in order to guarantee the customer SLA.

2 It is also possible to provide EPL and EPLAN using constant rate ATM or MPLS virtual circuits instead

of TDM circuits.


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EPL service is described in ITU-T G.8011.1 [10]. The EPL connection characteristics are

summarized in Table 3.

Table 3 EPL Connection Characteristics (Derived from ITU-T Rec. G.8011.1)


Network connectivity Point-to-point

Address - deliver unconditionally

Drop Precedence - not applicable


Class of Service

CustomerSeparation

Service instance

Spatial or logical (always connection oriented)

Link type Dedicated

Connectivity monitoring None, on-demand, or proactive

Bandwidth profile Committed information rate (CIR) and committee burst size (CBS)


VLAN ID is preservedPreservation

Class of Service is preserved


ITU-T G.8011.1 defines two types of EPL services:

Type 1 EPL, where the characteristic information (CI) transferred between the UNIs is the

Ethernet MAC frames. The Ethernet preamble, start of frame delimiters, and inter-frame

characters are discarded, and the Ethernet MAC frames are then encapsulated (for example,

into GFP-F) and mapped into the transport channel.

Type 2 EPL, which is only defined for 1 Gbit/s Ethernet, treats the 8B/10B line code

information as the CI to be transferred between the UNIs. The data and control code

information from the Ethernet signals 8B/10B line code characters are translated into a

more bandwidth-efficient 64B/65B block code, and multiple 64B/65B codes are then

mapped into a GFP frame (GFP-T).

The primary advantages of Type 2 EPL are the preservation of control codes (primitive

sequences of special line code characters) and lower mapping latency. While is possible to

also define Type 2 EPL for 4B/5B encoded 100 Mbit/s Ethernet, there has been no formal

request for this service so far.


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3.4 Ethernet Virtual Private Line (EVPL) Service

EVPL is also a line service; however, the line can be derived from a flow domain. It allows the

sharing of network resources among multiple customers or service instances in order to achieve

efficient use of those resources. EVPL is illustrated in Figure 2(b).

In addition to increasing the efficient use of transport network resources, another potential

advantage of EVPL is the reduction of the number of UNIs required at the customer edge. This

is illustrated in Figure 7 in Section 4.1. For the customer edge node on the left to connect to four

other nodes would require four different UNIs and their associated ports. Service multiplexing

is the packet multiplexing of multiple ECs onto a single UNI.

EVPL is specified in the ITU-T Recommendation G.8011.2. The EVPL connection

characteristics are summarized in Table 4. For virtual connections, the separation is typically

logical (that is, at the packet level). Due to the sharing of network resources, it is possible that

frames will be dropped because of congestion. In addition, as discussed above, a service

provider may wish to perform VLAN ID translation at the boundaries of the transport network.

Table 4 EVPL Connection Characteristics


Network connectivity Point-to-point


Drop Precedence (drop randomly or drop conditionally, depending on theExcess Information Rate (EIR) and Committed Information Rate (CIR)parameters)


Class of Service

CustomerSeparation

Service instance

Logical or spatial

Link type Shared or dedicated

Connectivity monitoring Sub-layer monitoring: On demand and/or proactiveInherent monitoring: Proactive

Bandwidth profile Specified Based on CIR and Committed Burst Size (CBS) (and in somecases also on EIR and Excess Burst Size (EBS))






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3.5 Ethernet Private LAN (EPLAN) Service

An EPLAN provides LAN-type connectivity between multiple customer sites through dedicated

channels. Figure 6 illustrates some of the different basic transport network topologies that can

support this service. From the customer viewpoint, these topologies are equivalent (that is, thecarrier network architecture is transparent to the customer).

Figure 6 EPLAN Illustrations

Carrier Network

CustomerEquipment

CustomerEquipment

CustomerEquipment

EthernetPHY

EthernetPHY

Ethernet

PHY

a) Mesh-type connectivity

CarrierNetwork

CustomerEquipment

CustomerEquipment

CustomerEquipment

EthernetPHY

EthernetPHY

b) Traffic hauled to a centralized switch point(s)

Carrier Network

CustomerEquipment

CustomerEquipment

CustomerEquipment

EthernetPHY

EthernetPHY

c) Edge node serves as a bridge or router


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In Options 1 and 3, the carrier does the switching at the edge of the network. Option 3 does the

switching at one end of the network rather than at each end. In Option 2, the traffic is brought to

a centralized switch (or a number of centralized switch points) in a star connection. Since the

switching is performed at Layer 2 in these examples, an MSPP can be used to implement

Options 1 and 3.

Open issues to be resolved for an EPLAN standard include:

How do the customer and carrier specify the bandwidth requirements? For example, if the

traffic was evenly distributed among the different customer nodes, the bandwidth between

nodes could be specified based on CIR. The more realistic scenario, however, is that

multiple customer nodes will want to simultaneously communicate with a single node (for

example, remote sites communicating with a headquarters office). A safe policy would be to

reserve enough bandwidth for each node to simultaneously receive data at full rate fromeach other node; however, this would too inefficient to be practical.

Closely related to the above issue, how much buffering must the carrier provide to handle

congestion, and what will the discard policy be?

Is protection handled at Layer 1 (for example, SONET APS) or Layer 2?

Although EPLAN is still under study, its expected connection characteristics are summarized in

Table 5.

Table 5 EPLAN Expected Connection Characteristics


Network connectivity Multipoint-to-multipoint (and probably point-to-multipoint)

Address - deliver unconditionally

Drop Precedence (for further study)


Class of Service

CustomerSeparation

Service instance

Spatial or logical (always connection oriented)

Link type Dedicated


Bandwidth profile Committed information rate (CIR) and committed burst size (CBS)


VLAN ID is preservedPreservation

Class of Service is preserved



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3.6 Ethernet Virtual Private LAN (EVPLAN) Service

EVPLAN is a combination of EVPL and EPLAN. The transport channel bandwidth is shared

among different customers, as are the routers in the carrier network. Ultimately, the sharing of

bandwidth in the transmission channels and switch fabrics gives EVPLAN the potential for verycost-effective carrier network resource utilization. Clearly, however, EVPLAN is the most

complicated network architecture to administer.

The open issues regarding EVPLAN transport architectures include all of those already

discussed for EVPL and EPLAN; although, the magnitude of some of these issues is greatly

increased for EVPLAN, which in turn restricts some of the potential solution space. For

example, the tagging mechanism to differentiate the data from different customers, and the

different data flows within each customer data stream, must have an adequately large address

space. (For example, the 4K-address space of VLAN tags makes them impractical for large

EVPLANs. Also, their applicability to only Ethernet frames further lessens their appeal for a

generic data network.)

Although EPLAN is still under study, its expected connection characteristics are summarized in

Table 11-7.

Table 6 EVPLAN Expected Connection Characteristics


Network connectivity Multipoint-to-multipoint (and probably point-to-multipoint)


Drop Precedence (drop randomly, drop conditionally, or not applicable)


Class of Service

CustomerSeparationService instance

Logical

Link type Shared


Bandwidth profile Specified

UNI list An arbitrary text string to uniquely identify the UNIs associated with the EC





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4 Ethernet Client Interfaces

The client interface (that is, the UNI) for Ethernet services will typically be an Ethernet physical

interface. In the past, the UNI for WAN data connections was typically based on telecom signals(for example, DS1, DS3, fractional-DS1, etc.), which required either special customer

equipment (for example, a T1 multiplexer) or special WAN port cards on customer routers.

Being able to use an Ethernet interface is advantageous for enterprise customers. Ethernet

interfaces are typically less expensive than telecom WAN interfaces, especially for higher bit

rates, and are supported by relatively inexpensive Ethernet LAN routers. Using an Ethernet

interface also allows enterprise network administrators to keep their OAM in the Ethernet

domain and allows carriers to handle the telecom signal domain.

The Ethernet UNI service attributes that are common for all services are shown in Table 7 and

the attributes that are service dependent are shown in Table 8.

Table 7 UNI Service Attributes Common to All Services

Layer UNI Service Attribute Service Attribute Parameters and Values

MAC service IEEE 802.3 frame format

UNI ID Arbitrary text string to identify each UNI instance

ETH

UNI EC ID Arbitrary text string to identify each EC instance

PHY speed 10 Mbit/s, 100 Mbit/s, 1 Gbit/s, or 10 Gbit/sETY

PHY medium IEEE 802.3 Physical interface

Table 8 Service-dependent UNI Service Attributes


Multiplexed access Yes, no

VLAN mapping Specify

Bundling Yes, no, all-to-one

Bandwidth profile For further study for most services

ETH

Layer 2 controlprotocol processing

Block, process, or pass per protocol on ingressGenerate, or none per protocol on egress

ETY PHY mode Full duplex, half duplex, or auto-negotiation

The UNI service attributes common to all services are reasonably self-explanatory so are not

discussed in this paper. The service-dependent attributes are explained as follows.

4.1 Multiplexed Access

This aspect of the UNI relates to whether a customer edge node has an individual UNI

associated with each of the far-end UNIs to which it is connected, or whether a UNI is shared

for the connections to multiple other customer UNIs. These cases are illustrated in Figure 7.


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Figure 7 Service Multiplexing Example

TRANSPORT

NETWORK

CE

CE

CE

CE

CE

4 x UNI

TRANSPORT

NETWORK

CE

CE

CE

CE

CE

UNI

a) Multiple point-to-point EPL

(one EVC per UNI)

b) Service multiplexed UNI(e.g., for multiple EVPL)

4.2 VLAN Mapping

Ethernet (per IEEE 802.1Q) allows the insertion of tags into Ethernet MAC frames in order to

create virtual LANs (VLANs). When a customer desires to preserve this VLAN segregation of

traffic through the WAN, the carrier may simply preserve the entire MAC frame, including the

VLAN tag.

It is possible that both the customer and service provider desire to use VLAN technology. If the

service provider also wishes to use VLAN technology, then it must either must insert a second(stacked) VLAN tag into the MAC frame, or perform a translation of the customer VLAN tag

at the ingress in order to conform to the service providers VLAN tag assignments, and then

restore the customer VLAN value at the egress.


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4.3 Bundling

Bundling refers to whether multiple customer VLAN IDs can be mapped into a single EC at a

UNI. The case where all VLAN IDs are mapped to a single EC is called all-to-one bundling. It

should be noted that all-to-one bundling and multiplexed access are mutually exclusive.Multiplexed access refers to the multiplexing of multiple ECs into a UNI. Mapping all VLAN

IDs into a single EC means that there is a single EC at that UNI rather than multiple ECs.

4.4 Bandwidth Profile

The bandwidth profile refers to the characteristics of the traffic that a customer presents to the

network at the UNI. The parameters include such things as guaranteed committed information

rate (CIR), peak information rate (PIR), burst sizes, and what is done with excessive traffic.

4.5 Layer 2 Control Protocol Processing

Layer 2 Control Protocols are used by enterprise network bridges for a variety of functions.

Depending on the protocol application and the WAN service, these protocols can either be

passed transparently through the WAN, processed (with the network provider equipment acting

as a peer to the customer equipment), or discarded at the UNI.

4.6 Summary of UNI Service Attributes for Different Services

The UNI service attributes are currently only defined for EPL service (ITU-T G.8011.1). These

attributes are summarized in Table 9. EVPL and EVPLAN (especially EVPLAN) will typically

make use of bundling and multiplexed access and have more complex bandwidth profiles.


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Table 9 Summary of UNI Service Attributes for EPL and EVPL Services


EPL

Multiplexed access NoVLAN mapping No

Bundling All-to-one

Bandwidth profile CIR, Committed Burst Size (CBS)

ETH

Layer 2 control protocolprocessing

All are passed except PAUSE frames, which are discarded.(The network equipment providing the UNI-N may generatePAUSE frames.)

ETY PHY mode Full duplex

EVPL

Multiplexed access Yes or No

VLAN mapping Yes or No

Bundling Yes or All-to-oneBandwidth profile For further study

ETH

Layer 2 control protocolprocessing

Specified in G.8011.2

ETY PHY mode Full duplex


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5 Protection and Restoration

For WAN transport, service protection is typically provided by the underlying transport

network. However, service restoration can also be provided only at the Ethernet layer usingEthernet protocols. Both approaches are summarized briefly here.

5.1 Service Protection or Restoration Provided by the TransportNetwork

Transport networks have traditionally been engineered for ultra-high service availability in

order to ensure reliable communications for emergency voice traffic. The objective is for a fault

to be detected and the service restored through a protection switching action within 60 ms

(10 ms for the detection and 50 ms to complete the switch). A protection switch action is

defined as the routing of the traffic from the failed facility or equipment to backup facilities or

equipment that has been reserved in advance3. In most cases, the protection channels arepermanently reserved, with their bandwidth either being unused during fault-free conditions, or

carrying low-priority traffic that can be dropped if the channel is required for protection. In the

case of TDM transport systems such as SONET/SDH, the protection switch is between TDM

channels or fibers [15]. In the case of ATM, the protection switch is between virtual circuits

[16].

The Link Capacity Adjustment Scheme (LCAS) provides an alternative approach for restoring

data services. For constant bit rate services such as voice, it is necessary to have protection

bandwidth that is at least equal to the service bandwidth. In the case of packetized data,

however, it is possible in many cases to maintain the service connection at a lower data rate inthe event of a network problem. LCAS provides this capability through its control of virtually

concatenated SONET/SDH, asynchronous/PDH, or OTH channels.

Virtual concatenation is the construction of a larger channel through the combining of multiple

smaller member channels. The data is then interleaved onto the constituent member channels in

a byte-by-byte round-robin basis. The individual members can take different routes through the

transport network with the network element (NE) that terminates the virtually concatenated

channel providing the buffering to compensate for the differences in delay that result from the

different routes. 4

3 In mesh networks that are constructed with digital cross connect systems (DCS), it is possible to have

the DCSs restore the traffic by communicating among each other to determine the protection path through

the network in response to a fault. While this approach typically allows the network operator to reserve

much less overall network bandwidth for protection, it can be difficult to meet the 50 ms switch time.

4 Virtual concatenation is described in S. Gorshe, A Tutorial on SONET/SDH, PMC-Sierra white paper

PMC-2030895.


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In the event that a subset of the members fail, the LCAS provides the signaling mechanism

between the virtually concatenated channels source and sink to allow the source to place the

traffic onto only those members that have not failed. This allows for a very powerful new

paradigm for network operators since, for services that can tolerate the reduced data rate during

faulted conditions, the operator can now provide very fast service restoration without having toreserve dedicated protection channels.

5.2 Service Restoration at Layer 2

When constructing a complex Ethernet network, it is important that only a single switching path

exist between any pair of nodes. Otherwise, loops would exist that cause instability in

forwarding tables and would cause broadcast data to be unnecessarily multiplied (that is,

broadcast storms).

The Ethernet solution to this issue is the spanning tree protocol (STP). The STP sends Layer 2

control protocol messages between the Ethernet nodes in order to establish an overlaid logicaltree structure on the network. Messages are periodically sent between adjacent nodes to confirmthat no changes have occurred to the network connectivity. When a fault occurs, the node

detecting the failure (that is, the change in network connectivity) will initiate a new spanning

tree construction. The network is then unavailable for the 30 to 60 seconds that it can take for

the STP to resolve. A new rapid STP (RSTP) protocol has been developed, but it still takes

seconds to resolve.

While this is a very powerful and flexible service restoration tool, there are several issues when

it is applied to Ethernet WAN services. Of course, the larger the network in terms of number of

nodes and geographical reach, the slower the STP resolution. Another potential issue occurs if

the network operator uses Ethernet routing technology within its network. Here, conflicts

between customer and network operator STPs must be avoided. Another issue is the interactionof the 50 ms protection switching (for example, SONET/SDH) with the STP. If the Ethernet

node and the transport network node both detect the fault, it would cause unnecessary extended

network unavailability if the STP were initiated for a fault that will be quickly protected by the

SONET protection switch. It is desirable, then for the Ethernet node to wait at least 50 ms to see

if the problem clears before it initiates the STP.


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6 Conclusion

A convergence of technology and applications has increased the importance and value of wide-

area Ethernet data transport services. This white paper has introduced some of the newtechnology and standards in development that will enable carriers to provide these services.

This includes a discussion of Ethernets connection services, client interfaces, and protectionand restoration abilities.

What makes the development of Ethernet transport service attractive is its evolutionary

approach. It builds on the customers capital investment in Ethernet technology, and the

transport providers existing SONET/SDH backbone networks and OAM procedures. All of the

pieces are currently in place for offering EPL services. The tools and standards to provide the

more complicated ELAN, EVPL, and EVPLAN services are currently being developed by the

various standards bodies.

While some proprietary data transport solutions exist, carriers require standards-based solutions,which Ethernet data transport provides, for any significant deployment of new services. The use

of standards helps guarantee that the solution will be available from multiple vendors, will be

stable and supported for many years, and ideally will be less expensive due to economies of

scale. While each carrier will probably want to offer variations on the basic service types in

order to differentiate themselves from their competitors, the services discussed in this paper

provide the framework from which they can build.


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A Related Standards Activity

The information in this white paper primarily focuses on the output of the Ethernet transport

work in ITU-T Study Group 15 (SG15) and its series of new standards. SG15 is the ITU-T bodyresponsible, among other things, for standards related to public transport networks.

The current level of standards activity is a good indication of how many companies and

organizations see Ethernet WAN as the next key step both for Ethernet and for the public

transport network providers (that is, carriers). The major standards activities and their status are

summarized in Table 10.

Table 10 Summary of Related Standards Activities

Organization Activities Status

IEEE

802.3ae 10 Gbit Ethernet, which includes a WAN PHY interface to simplifyinterfacing to a SONET/SDH or G.709 OTN network

Approved

802.17 Resilient Packet Rings: Working on a ring-based network foraccess and metro applications

Approved

802.3ah(EFM)

Ethernet in the First Mile, where work includes OAM aspects forEthernet Links (especially access links)

Approved

802.1 ad Provider Bridge specification This is the Q-in-Q standard. In Progress

802.1ag Connectivity Fault Management, or Ethernet Service OAM In Progress

802.1ae MAC Security (MacSec), including authentication, authorizationand encryption

In progress

ITU-T SG15(With input from ANSI T1X1)

G.8011.1(Q11)

Ethernet Private line service Approved

G.8011.2(Q11)

Ethernet Virtual Private line service Approved

G.8012(Q11)

Ethernet UNI and Ethernet Transport NNI Approved

G.8010(Q12)

Ethernet Layer Network Architecture, which is largely to translatethe IEEE 802 network material into ITU-T transport networkterminology and models

Approved

G.8011(Q11)

Ethernet over Transport Ethernet Service Characteristics Approved

G.esm

(Q12)

Ethernet over Transport Ethernet Service Multiplexing, which

covers the multiplexing protocol(s) required to implement EVPLand EVPLAN

In Progress

G.8021[7](Q9)

Characteristics of Ethernet transport network equipment functionalblocks

Approved2004 (1stphase)

Y.ethps

(Q3)

Ethernet protection switching In progress

Q2 Studying Ethernet OAM aspects relating to access In progress


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Organization Activities Status

ITU-T SG13

Y.1730 Requirements for OAM functions in Ethernet-based networks andEthernet services

Approved

Y.ethoam

(Q3)

End-to-end and edge-to-edge aspects of Ethernet OAM includingPM

In progress

Metro Ethernet Forum (MEF)

The MEF is studying various aspects of Ethernet MANs, including Ethernet architecture, service model,service definition, traffic management, UNI and NNI definition and OAM. The MEF work is covering allpossible OAM flows, such as end-to-end, edge-to-edge, access, inter-provider, intra-provider, etc.

MEF1 Ethernet Services Model, Phase 1 Approved

MEF2 Requirements and Framework for Ethernet Service Protection inMetro Ethernet Networks

Approved

MEF3 Circuit Emulation Service Definitions, Framework andRequirements in Metro Ethernet Networks

Approved

MEF4 Metro Ethernet Network Architecture Framework - Part 1: GenericFramework Approved

MEF5 Traffic Management Specification: Phase I Approved

UNI Type 1 Specification of UNI, data-plane aspects In progress

UNI Type 2 Specification of UNI, control-plane aspects (ELMI) In progress

EMS-NMS MIBS for Ethernet and network management In progress

MEF Architecturepart 2

Specifies functional elements of Ethernet trail, such as adaptation,conditioning, etc.

In progress

CES PDH Implementation agreement of PDH CES over Ethernet (includesboth AAL1 and Raw method)

In progress

Internet Engineering Task Force (IETF)

PWE3 WG Working on defining an Ethernet transport over IP/MPLS usingMartini drafts (this is mainly EVPL service using UDP, L2TP orMPLS as multiplexing layer)

In progress

PPVPN WG Requirements for Virtual Private LAN Services (VPLS) In progress

L2VPN WG Working on framework and service requirements of Ethernet-basedVPN, and defining EVPLAN service using IP/MPLS

In progress

Note that each standards organization has its own areas of expertise. The majority of the

standards that will be required for the public transport network are being developed in the Q12

and Q11 groups of ITU-T SG15. This work was partitioned not only logically by topic, but also

in a manner that allowed for the earliest possible approval of useful standards/

recommendations. The initial set of standards was approved in mid-2004 (see Table 10).

ITU-T SG15 has established liaison contact with the other standards organizations and forums

where their input is required or desired. For example, the G.ethsrv work is expected to use a

considerable amount of input from the MEF regarding the definition of services.


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B Definitions

The source of these definitions is the G.809 ITU-T recommendation.

Term Definition

Access group A group of co-located "flow termination" functions that are attached to thesame "flow domain" or flow point pool link".

Characteristic Information(CI)

A signal with a specific format, which is transferred on "flows". The specificformats are defined in technology-specific standards.

Flow An aggregation of one or more traffic units with an element of commonrouting.

Flow domain A topological component used to effect forwarding of specific characteristicinformation.

Flow point A "reference point" that represents a point of transfer for traffic unitsbetween topological components.

Flow point pool A group of co-located flow points that have a common routing.Flow point pool link A "topological component" which describes a fixed relationship between a

"flow domain" or "access group" and another "flow domain" or "accessgroup".

Flow termination A "transport processing function". There are two types of flow termination, aflow termination sink and a flow termination source.

Link flow A "transport entity" that transfers information between "ports" across a flowpoint pool link.

Topological component An architectural component, used to describe the transport network in termsof the topological relationships between sets of points within the same layernetwork.


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C References

[1] ITU-T Recommendation G.709 (2001), Interfaces for the optical transport network

(OTN).

[2] ITU-T Recommendation G.707 (2003), Network node interface for the Synchronous

Digital Hierarchy (SDH).

[3] ITU-T Recommendation G.7043/Y.1343 (2004), Virtual concatenation of Plesiochronous

Digital Hierarchy (PDH) signals.

[4] ITU-T Recommendation G.7042 (2004), Link Capacity Adjustment Scheme (LCAS) for

Virtual Concatenated signals.

[5] ITU-T Recommendation G.7041/Y.1303 (2003) - The Generic Framing Procedure (GFP).

[6] ITU-T Recommendation G.8040 (2004), GFP frame mapping into Plesiochronous Digital

Hierarchy (PDH).

[7] ITU-T Recommendation G.8021/Y.1341 (2004), Characteristics of Ethernet transport

network equipment functional blocks.

[8] ITU-T Recommendation G.809 (2003), Functional architecture of connectionless layer

networks.

[9] ITU-T Recommendation G.8011/Y.1307 (2004), Ethernet Services Framework.

[10] ITU-T Recommendation G.8011.1/Y.1307.1 (2004) Ethernet Private Line Service.

[11] ITU-T Recommendation G.8011.2/Y.1307.2 (2005) Ethernet Virtual Private Line Service

[12] ITU-T Recommendation G.8012/Y.1308 (2004), Ethernet UNI and Ethernet NNI.

[13] ITU-T Recommendation G.805 (2001), Generic functional architecture of transport

networks.

[14] ITU-T Recommendation G.8010/Y.1306 (2004), Ethernet Layer Network Architecture.

[15] ITU-T Recommendation G.808.1 (2003), Generic Protection Switching Linear Trail and

Subnetwork Protection.

[16] ITU-T Recommendation I.630 (2000) ATM Protection Switching.


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Contacting PMC-Sierra

PMC-Sierra

8555 Baxter PlaceBurnaby, BC

Canada V5A 4V7

Tel: +1 (604) 415-6000

Fax: +1 (604) 415-6200

Document Information: [email protected]

Corporate Information: [email protected]

Technical Support: [email protected]

Web Site: http://www.pmc-sierra.com
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