What Is Metro Ethernet

Published Date: 02 Nov 2017

Chapter 1

Introduction

A Networking and telecommunication technologies in today’s world is for communication, data transfer, sending information, download/upload data and much more. It’s been used in many sectors such as business, education, medical, and government. This research focus on two specific networking and telecommunication technology, that can transfer or backup data faster than normal networking; the Metro Ethernet (Metro E) and Leased Line which is currently being used by Total Sdn Bhd. These networking technologies use a point to point connection and offered high speed data transfer from one location to another.

The bandwidth speeds offered by Metro E services are available in a range of 10Mbps to 10Gbps. However, Leased Line on the other hand only offered bandwidth speeds from 64Kbps up to 2Gbps. Metro E and Leased Line do have their advantages and disadvantages. Metro E able to carry high bandwidth, cost effective and many more, while Leased Line offered a limited bandwidth and upgradeable with additional cost.

Leased Lines are typically used by business to connect geographically distant offices and unlike a normal dial-up connections, a Leased Line is always active. Normally, the fee for the connection is chargeable as one fixed monthly rate. The main factors affecting the monthly fee are the distance between end to end points and the speed of the circuit itself. Due to the fact that the connection does not carry anybody else communications, thus the carrier can assure the level of quality. A Leased Line is a premium internet connectivity product which is delivered via fiber connection which normally is dedicated and provides symmetrical speeds, uncontended and full-duplex. It is also known as an Ethernet Leased line, private circuit or data circuit and DIA line.

Metro E network is a metropolitan area network (MAN) that is based on Ethernet standards. It is normally used to connect subscribers to a larger service network or the Internet. Metro E is also used by businesses to connect their own offices with each other. An Ethernet interface is much less expensive compared with a Synchronous Digital Hierarchy (SDH) interface of the same bandwidth. Ethernet also supports high bandwidths with fine quality, a feature that is not available with traditional SDH connections. Another advantage of an Ethernet based access network is that it can be easily connected to the customer network. A typical service provider’s network is a build-up from a collection of routers and switches connected through optical fiber. The topology type could be a ring, hub and star or full/partial mesh.

1.1 Problem Statement

Currently, company Total Sdn. Bhd. is using a leased line to transmit, exchange and backup data to their office branches and their disaster recovery site (DR). Due to overwhelming volume of data transmitted every day because of the expansion of business, the current leased line need to upgrade or can become as a backup line. As a company’s infrastructure engineer, management has requested to provide a solutions and full documentation as a proposal to the management. Metro E is one technology that is capable of becoming an alternative to the leased line. This documentation will include a full research on Metro E including aspects of security, stability, capabilities and the implementation.

Management has willing to invest in this technology without hesitation regardless the cost of upgraded because it impacted the business and company profit. The cause of these issues as follows:

Massive amount of data transmitted every day (new branches open)

Increasing numbers of users

Repetitive issue on slowness and connection stability

Expansion of data center (increasing of servers)

Impacted of the issues:

Low productivity due to unstable and slow connection

Bias of the daily work flow

Bad company reputation

Increasing cost of operation

1.2 Problem Explanations

With the new branches established, the massive and overwhelming data transmitted every day between branches and Headquarters and also to DR site in order to backup daily data. All the issues are related each other, the massive data transmitted every day because of increasing of users and expansion of data center (increasing of servers) and these causing the slowness of the network and impacted all users, customers and daily business.

1.3 Limitations of Research

There are limitations in this research but this research still able to do it. The limitations of this research as follows:

All the information in this research has to be change and modified according to the real event.

This research and problem about company Total Sdn Bhd (not actual name) only and maybe others company not facing these kinds of issues.

Employees and board of director has prohibited revealing the private and confidentiality of data, network structure, company operation, financial and company infrastructure because it’s against the company policy.

Time limit, this research was conducted in short time of period because business wanted to be done as fast as possible.

Access to information and resources.

Task overloaded.

1.4 What is Leased Line?

Currently Total Sdn Bhd is using a Leased Line (1Mbps) to transfer daily data, data backup, video conferencing and so on. What is Leased line? Leased Line is a service contract between a provider and a customer whereby the provider agrees to deliver a symmetric telecommunications line connecting two or more locations and in exchange company pays the monthly rent. In the United Kingdom, it is sometimes known as a "data line" or "private circuit". Unlike traditional PSTN lines, it does not have a telephone number at each side of the line that is permanently connected to each other. Leased Lines can be used as telephone, data or Internet services with some are ringdown services and some connected to PBXes.

Often, businesses will use a Leased Line to connect others distant offices mainly because it guarantees the bandwidth stability for network traffic. For example, our companies Total Sdn Bhd use a leased line in order to easily transfer data backup, financial information from one branch office to another. Both long and short distances can be spanned by a leased line and customers generally pay a flat monthly rate for the service. A long time ago broadband Internet access was readily available, a company cost was charged according to the distance between the two points, more recently leased line replacement services allow a user to upgrade and improve the lines with fees that are per-end only.

Figure 1: Overview of Leased Line System

1.5 What is Metro Ethernet

Metro Ethernet (Metro E) is using the Ethernet technology in a Metropolitan Area Network (MAN) that connects businesses and subscribers to a Wide Area Network (WAN) and the Internet, or connects their branch offices to an Intranet. Ethernet is the local area network (LAN) technology that installed widely, which is designed to support a high bandwidth with fine features and functions as a family of frame based computer networking technologies for LAN. Ethernet stations are able to communicate by sending data packets and user blocks data. Every Ethernet station receives a MAC address, which is specifies both the source and the destination of each data packet. Normally, Ethernet is used in corporate and residential networks.

Ethernet based access networks are easy to implement into a customer network and cost effective and this drive its ubiquity. Typically, there are a few collections that Metro E consists of, such as layer 2 and/or layer 3 switches and/or routers that connected through optical or cable. In MAN environment Ethernet deployed as a pure Ethernet. Other types of Ethernet are Ethernet over Multiprotocol Label Switching (MPLS), Ethernet over DWDM or Ethernet over synchronous Digital Hierarchy (SDH). Pure Ethernet however is comparably inexpensive to the latter technologies.

According to IT Quotes from their website,

"Metro Ethernet Service is a private data connection securely connecting two or more locations in a metropolitan area with Ethernet data speeds. A metro Ethernet circuit is a closed network data transport service which does not traverse the public Internet and is inherently secure with no data encryption needed (IT Qoutes, 2012)"

The bandwidth speeds offered by Metro E services are available in a range of 10Mbps to 10Gbps. A Metro E private line is not a shared service connection and follows the same secure direct network path every time, therefore it provides unparalleled quality of service (QOS). Typically, Metro Ethernet circuits are used by businesses to provide secure Ethernet point to point data service and reliability. These connections will then be used for applications such as credit card processing, file sharing, data backup, Ethernet VOIP and video conferencing. A Metro E circuit can also be configured to carry voice, video, Internet and data services together over the same Ethernet connection. Metro E Private Line or Metro Optical Ethernet refers to a point to point Metro E services. When a user-network interface (UNI) is installed by the service provider with one side consists of the customer equipment and the other being the Metro E network, the connection is established.

In order to establish Layer 2 connectivity between two locations, exactly like a wired network connection between two locations, an Ethernet Virtual connection will makes the path between the interfaces possible and maintain the Ethernet MAC address and frame contents unchanged. Metro E has become the service of choice for many companies, particularly with IT groups which normally consist of several branches that have two or more separate businesses in a local area. Even big corporations, government agencies and academic institutions in Washington D.C, Baltimore and New York City also use Metro E to achieve a high-speed, secure and affordable connectivity.

A lot of service providers nowadays offering Metro E services. Some of them have extended Ethernet services beyond the metropolitan area and across the wide area. Ethernet services, in the other hand have been subscribed by thousands customers and their numbers are growing rapidly around the world. Telekom Malaysia or better known as TMNet is the main service provider in Malaysia. These subscribers have been attracted by the benefits of Ethernet services including:

Ease of use

Cost effectiveness

Flexibility

Figure 2: Overview of Metro E System

1.6 Conclusion

With the current leased line, company Total Sdn Bhd is facing the impact of overwhelming the data transmit every day, slowness, increased cost of operation and daily work flow and bad company reputation because of the increasing of users, servers and expansion of data center. Metro E is one of the solutions available in nowadays technology that can offer better performance, stability, security, capabilities and cost effectiveness. In the next chapter we will see more research details about Metro and the implementation. With this upgrade and research, it changing the whole daily work flow of company Total Sdn Bhd, users experience, quality of service and customers satisfaction.

Chapter 2

Why Use Metro Ethernet?

Nowadays, 98% of data traffic are in enterprise LANs and end on an Ethernet port. With 30 years of great history in Enterprise LANs, it has become the most dominant standard protocol in the networking industry. From cost and technical perspective, Metro E has become an obvious choice if enterprises are looking at achieving a stable connectivity beyond their LANs. A corporate network that are connected or interconnected within a MAN, tends to create a bottleneck issue. The bandwidth has increased over 300 fold in the backbone and 100 fold in access, but only a 16 fold in the Metro E. Thus, this has produced a significant Metro E bottleneck. Due to that, the enterprise customers are started to push service provider to connect their sites via Metro networks, but the leased line could not provide a flexible bandwidth to cope with the demand to compete with Optical Ethernet.

Deploying Gigabit Ethernet based platforms in the MAN areas is a compelling and commercially proven approach to break the metro bandwidth bottleneck for the following reasons:

Cost effectiveness

Infrastructure equipment cost for Ethernet are significantly less than leased line or frame relay (FR) or ATM costs. This is due to the economies of scale arising from the existing installed base of Ethernet that ensures lower material and development cost and also the relative technical simplicity of Ethernet. Provisioning costs or mainly operational and planning related costs are also significantly less than TDM (SONET/SDH, T1/E1, and T3/E3) with comparatively effortless adoption and higher available data rates as an added bonus.

Rapid Provisioning on Demand

From a service provider perspective, service velocity is a key competitive differentiator. The present lacks of customer centric flexibility as well as the coarseness of bandwidth granularity of TDM and ATM legacy systems are seen to be major impediments to providing promising revenue generating services. On the other hand Ethernet access services offer a wide range of speeds from 10Mbps to 10Gbps which can provide on demand and quickly.

Packet Based

Ethernet is an asynchronous frame-based technology that has particular flexibility advantages over its more rigid cell-based or synchronous competitor. With suitable rate limiting functions to manage available resources and with sufficiently large trunk capacity, Ethernet can provide rapid bandwidth on demand.

2.1 Metro Ethernet Architecture

This explaination and research provides the generic architectural framework for Metro-E Network (MEN). The architecture framework describes the high level constructs used to model the various architectural components of MEN’s Ethernet services, transports services and application services layer networks. Architecture model is based on the principle of layer network decomposition. Each layer network is constructed from a particular set of networking technologies for example Ethernet, SONET/SDH and MPLS. The model reuses the native Ethernet frame structure and the architectural constructs created to describe connection and connection-less oriented transport networks in ITU-T recommendations G.805 and G.809.

The architecture framework describe the internal and external architectural components of a MEN in terms of Ethernet services, transport services and application services layer networks components and the generic architectural components associated with layer networks that is used by Metro E. It is also used to describe the interactions among MEN architectural components across well defined interfaces and their associated reference points. The architecture framework is not intended to require or exclude any specific networking technology from being used on any given implementation of MEN, but instead it provides the common guidelines for the specification and decomposition of the MEN Ethernet transport and services capabilities.

2.1.1 Terminology

Terms

Definition

APP

Application Services Layer

ATM

Asynchronous Transfer Mod

CE

Customer Edge

CI

Characteristic Information

ESD

Ethernet Services Definition

ESM

Ethernet Services Model

ETH

Ethernet Services Layer

EVC

Ethernet Virtual Connection

FE

Functional Element

GbE

Gigabit Ethernet

IEEE

Institute of Electrical and Electronics Engineers

IWF

Interworking Function

ITU

International Telecommunication Union

L1

Layer One

L2

Layer Two

L2+

Layer(s) above L2

LAN

Local Area Network

MAC

Media Access Control

MEN

Metro Ethernet Network

MPLS

Multi Protocol Label Switching

NE

Network Element

NI-

Network Interworking (e.g., NI-NNI)

NNI

Network-to-Network Interface

NT

Network Termination

OTN

Optical Transport Network

PDH

Plesiochronous Digital Hierarchy

PE

Provider Edge

RPR

Resilient Packet Ring

SDH

Synchronous Digital Hierarchy

SI-

Service Interworking (e.g., SI-NNI)

SNI

Service Node Interface

SONET

Synchronous Optical Network

TE

Transport Equipment

TRAN

Transport Services Layer

UNI

User to Network Interface

VLAN

Virtual LAN

WAN

Wide Area Network

2.1.2 MEN Layer Network Model

The MEN layer network model specified in this architecture framework defines the MEN in terms of three layer network components:

Ethernet Services Layer - supporting basic Layer 2 (L2) Ethernet data communication services

Transport Services Layer – can be a set of one or more

Application Services Layer – optional layer that support applications carried on the basic L2 Ethernet services.

The layer network model is based on client-server relationship. In addition, each of these layer networks may be further decomposed into their data, control and management plane components, this layer network view of a MEN is shown in Figure 3 below.

Figure 3: MEN Layer Network Model

2.1.3 Ethernet Service Layer (ETH)

The Ethernet Service Layer also referred to as the ETH Layer. It is responsible for the Ethernet MAC oriented connectivity services and the delivery of Ethernet service frames presented across well defined internal and external interfaces and associated reference points and also responsible for all service-aware aspects associated with Ethernet MAC flows including operations, administration, maintenance and provisioning capabilities required to support such Ethernet connectivity services.

2.1.4 Transport Service Layer (TRAN Layer)

The Transport Layer also known as TRAN Layer supports connectivity among ETH layer functional elements in a service independent manner. It uses many layer network technologies and approaches to support the transport requirement for the Ethernet services layer. IEEE 802.3 PHY, IEEE 802.1 bridged networks, SONET/SDH High Order/Low Order path networks, ATM VC, OTN, PDH and MPLS LSP are among the example of transport layer networks. Those transport layers are supported by their respective server layers for example SDH STM-N Multiplex Section, ATM VP and Fiber. Probably this model applied recursively downwards into the transport layer network stack until the physical transmission medium (wireless, fiber, coax, copper) is reached.

2.1.5 Application Service Layer (APP Layer)

The Application Service Layer or the APP Layer support applications that are carried on the basic Ethernet services across the MEN. Various application services may be supported over the basic Ethernet services supported by the Ethernet service layer. The example of APP layer is the use of ETH layer as a TRAN layer for other layer networks such IP, MPLS, PDH. This layer also include add on functions to complement ETH layer services and each may support one or more application services layers. The model may be applied recursively upwards into the application layer network stack.

2.1.6 Metro Ethernet Reference Model

There are two major functional components that involved in MEN (refer Figure 4) which is the basic network reference model of a MEN.

The subscriber/customer edge equipment

The public MEN transport infrastructure

Figure 4: Basic Network Reference Model

Point T is referred to the UNI reference point and become the boundaries between the public MEN and a private customer network. Point S is referred to the conceptual points that become the boundaries between the private customer network equipment. Point S and Point T will coincide if no private network infrastructure exists between subscriber terminal equipment and public Metro Network Equipment. End user terminal will generating Ethernet frame flow. The frame flow (Ethernet) might be a non-contiguous. For example, consecutive Ethernet frames may belong to a different flows and share of common treatment unidirectional stream frames for transfer across the MEN. In details, Ethernet flow end to end show the flow between Ethernet frames and communicating terminal and terminates the Ethernet frames.

In order to deliver an Ethernet flow between subscriber sites to the MEN, the Ethernet Virtual Connection (EVC) is the architecture construct that supports of UNI reference points. A particular EVC may be mapped to one or more subscriber flows, for example may be more subscriber flows determined by the classification rules of flow at the ingress point to a network then EVC (MEN Forum, 2004).

The basic MEN reference model shown in Figure 3 above is presumes of a one to one relationship between the MEN service provider port and MEN subscriber port. It means access into the service provider equipment supporting the UNI functions indirectly, for example where Ethernet services are introduced over pre-existing access technologies via so called feeder or Access Networks may be required in deployment scenarios (PDH, SONET/SDH Fiber/Coaxial networks) or over an alternative Ethernet transport facilities.

2.1.7 User Network Interface (UNI) and UNI Network

In order to interconnect a MEN service provider and MEN subscriber the UNI is the interface used. MEN operator equipment that enables access to MEN services and subscriber access equipment also using UNI as reference point. Hence the point stated the location where the responsibility of subscriber begins and responsibility of the service provider ends. MEN component that represents all the functions that connect from MEN to MEN subscriber is a UNI-N, UNI-N is a compound architectural. In subscriber perspective UNI-N functions is to control, exchange data and management plane information with the MEN. UNI-N is entirely in the service provider and network operator domain. The functions of UNI-N include with the transport network infrastructure and Ethernet services infrastructure.

2.1.8 External Network to Network Interface (E-NNI) and Internal Network to Network Interface (I-NNI)

The E-NNI is an open interface that interconnects between two MEN service providers. Reference point for Ethernet service and network equipment that directly attached to MEN provides by the E-NNI and also for Network Element (NE) and Ethernet service between Ethernet services aware Wide Area Network (EWAN) and MEN. Transport interfaces and Network Interworking capabilities that associated with native Ethernet physical interfaces may be supported across this interface. For your information E-NNI also refers to generically to the protocol exchange that exists at the E-NNI reference point in each of the MEN that support E-NNI delineation functions. It does exist between the architectural elements.

The I-NNI is an open interface that used to connect NE from MEN service providers. Reference point for Ethernet service between these two is directly attach to NE. Transport interfaces and Network Interworking capabilities that associated with native Ethernet physical interfaces may be supported across this interface. Plus, I-NNI also refer generically to the protocol exchange that exists at the I-NNI reference point in each of the MEN that support the I-NNI delineation functions.

2.1.9 Network Interworking Network to Network Interface (NI-NNI) and Service Interworking Network to Network Interface (SI-NNI)

The extension of transport facilities used to support Ethernet services and associated EVC over an external transport networks is not directly in the end to end Ethernet service and also supported by the NI-NNI. The intention of NI-NNI is to preserve the characteristic information of a subscriber flow. Reference point that provides by NI-NNI between two MEN service provider interfaces is attached via public transport networks.

The examples of public transport networks are OTN, SDH/SONET, ATM, Frame Relay, and RPR and so on. In this research the term NI-NNI is refer to the protocol exchange that exists at NI-NNI reference point and the architectural. It does exist in each of the MEN responsible for the support of the NI-NNI delineation functions (NI-NNI IWF).

The interworking of MEF service with services provided via other service enabling technologies is support by SI-NNI interface, for examples Frame Relay, ATM and IP. Reference point for another public service network and MEN also provides by the SI-NNI. The examples of public network include ATM, Frame Relay and IP. In this research the term SI-NNI is refer to the protocol exchange that exists at the SI-NNI reference point and the architectural element. It does exist in each of the MEN responsible for the support of the SI-NNI delineation functions (SI-NNI IWF).

2.1.10 Service Node Interface (SNI)

Service Node Interface is one of the interfaces that have ability to supports the extension of the MEF UNI capabilities across an intermediate access network not directly involved in the end to end Ethernet service. A reference point that provides by SNI between a packet aware Access Network between the network location where Ethernet Service attributes are enforced that aggregates subscriber flows at a packet level (L2) into a common transport channel (refer Figure 5). In this case reference point for UNI and SNI are equivalent to V (VB) and T (TB) in the ISDN (B-ISDN) terminology. The packet based transport function for the access portion of the connection between the MEN and subscriber are strictly provides by the Access Network. Informally, SNI reference point also referred to the Virtual UNI reference point and the SNI preserve in a transparent manner the characteristic information of a subscriber flow.

Figure 5: Reference Point for Access Arrangements into MEN via SNI

2.2 MEN Architectural Components

The approach functional modeling is used in this framework to represent various architecture components of the layer network of MEN. It is based on the architectural constructs that created to describe connection-less oriented and connection oriented transport networks in ITU-T Recommendations G.805 and G.809. In this chapter will describe the main architectural concept that has been defined by these two Recommendations as related to Metro Ethernet Forum architecture framework. There are three types of architectural components are defined:

Topological components

Transport components

Processing components.

Transport and topological components are used to represent abstract connectivity constructs while processing components are used to represent abstract system components that affect information transfer. These formal definitions of topological components, transport entities and reference points can be found in the ITU-T Recommendations G.895 and G.809 for further reading (TU-T Recommendation G.805 "Generic functional architecture of transport networks." March 2002 and ITU-T Recommendation G.809 "Functional architecture of connectionless layer networks." March 2003).

2.2.1 Topological Components

The highest level of abstraction for the description of an architectural component of a transport network is provides by the topological component. It defines exclusion and inclusion relationships between sets of like associated reference points and functions. There are four topological components of interest as below:

Subnetwork: A block or partition of a layer network used to affect the steering of specific user data within a portion of layer network. Subnetwork is reserved for connection oriented networks in the ITU-T terminology. The context of a connectionless layer network like Ethernet is used in the term Flow Domain.

Layer Network: the complete set of physical (see access group) and logical ports of the same type maybe associated for the purpose of transferring information. Information transferred is in terms of a well defined traffic unit of the particular layer network and it is termed its Characteristic Information (CI).

Link: The relationship connectivity between a "access group" or "subnetwork" and another "access group" or "subnetwork" is fixed. The context of a connectionless layer network such Ethernet are user in the term Flow Point Pool Link.

Access Group: Physical ports or a group of co-located logical with associated processing functions that are connected to the same "link" or "subnetwork". An access group represents flow domain or the logical access ports into a given sub-network.

The CI format is always defined in a technology specific manner for each network layer in their associated architecture framework. It is used to specify units of information including a specific unit format and transferred on connection within the given layer network. The Ethernet MAC layer such as the IP network layer, the SONET/SDH High Order/Low Order layers or even a fiber infrastructure are example of layer networks.

2.2.2 Transport Components

A transport entity or transport component means to affect the transfer of information between reference points. There are two types of transport entities and associated reference points are defined:

Connection: It represents an aggregation one or more connection oriented traffic units with a common routing. Referred as a flow in connectionless layer network .

Connection Point: It represents a location of transfer of topological components between connection oriented traffic units. Referred to as flow point pool/flow point in connectionless layer network.

Trail: Trail is a transport entity represents the transfer monitored and adapted characteristic information of client network between two access points. In other words it represents the association between destination and source one traffic unit basis. Referred to as a connectionless trail in connectionless layer network.

Trail Termination Point: It represent a location of extraction and insertion of monitored and adapted information characteristic to a given layer network and it opposed to the information presented by the client of the layer network. Referred to as flow termination point in connectionless layer network.

Access Point: Access point is the reference point where the input (output) of an adaptation is bound to the output (input) of a trail termination or the output of an adaptation function.

2.2.3 Processing Components (MEN Functional Elements)

The actual means provides by processing component is to the affect the transfer of information at a given reference point. In this architecture framework the concept of Functional Element is used to represent the specific set of processes or functions within the MEN services or transport network. It acts on a particular collection of input data to produce a specific collection of output data. FE also used to represent compound functions for example collection of other pre-defined functional elements.

The intention of the MEF architecture framework is to adopt the existing functional elements and also associated functional models. In addition, functional elements for Ethernet LAN are derived from IEEE 802.1Q-1998 and IEEE 802.3-2002 specifications. Functional models for connection oriented functional elements from ITU-T Recommendations G.805 and for connectionless functional elements from ITU-T Recommendations G.809. The details functional models for the functional elements in the MEN architecture will not discuss in this research document.

2.3 Layers (MEN) Relationship to the Architectural Model Components.

This topic will discuss the relationship between ETH, TRAN and APP layers, the generic topological components and operational planes. There are 3 operational planes:

Data plane

Control plane

Management plane

The Data Plane itself referred to as forwarding plane, user plane and transport plane. It required to steer the subscriber flow provides by the functional elements and also support the transport traffic units (subscriber) among MEN Network Elements.

In order to support distributed flow management functions among Network Elements participating in MEN data plane is provides by the Control Plane and also to support supervision, connection release operations and distributed set up among other flow control functions. For the Management Plane it provides the functional elements that support Fault, Configuration, Account, Performance and Security (FCAPS) including flow and connection configuration functions and also any related Operations, Administration and Maintenance (OAM) tools.

External and subscribers network that connected to MEN mostly likely to include similar layers and planes. The information exchange between the Control Planes, MEN Management and subscriber at the reference points is restricted or may be absent followed by the implementation agreements for the UNI, NNI and other external IWF.

2.4 Topological Components and MEN Network Reference Model

Metro Ethernet Network consists of logical components for example meters, policers, shapers, virtual switches and links. It also consists of physical components like network elements and ports and so on. The MEN architecture is described as the associations between points in the network and functional components or the interconnected topological. There is partition of MEN into layer networks that bound the scope of various MEN topological and functional components. In a client-server relationship access groups connect customers from client layer network to the service that supported by the server layer network. In addition any binding between input and output of processing functions or transport entities describes as reference point.

Figure 6 below shows the relationship between MEN reference model, topological components and its network layer networks. In a particular service provider network multiple Ethernet layer network domains for example (ETH Subnetwork A and ETH Subnetwork B) and to instantiate a particular MEN a different kinds of transport technologies is used (maybe) for example (TRAN Subnetwork B and TRAN Subnetwork C).

Figure 6: Sample Relationship between MEN Reference Model and Architectural Components

Take note IP, MPLS, SONET/SDH and PDH may play as a dual role with the Ethernet services layer:

Role as an application service layer

Role a transport layer providing transport services

For example, the Application Layer and Transport Layer maybe divided into partitioned in associated protocols and additional layer networks. You can see the layer network modeling principle below (Figure 7).

Figure 7: Sample Decomposition of Protocol Stacks and MEN into Layer Networks

2.5 Metro Ethernet Reference Link Model

The word "link" that mentioned in this architecture framework refer to a "topological component" that show a fixed connectivity relationship and available transport capacity between pair of subnetworks which is flow domains or an access group and subnetwork (flow domain) or a pair of access group. Links are example of classified for the MEN layer network they support and the relationship to external and internal reference point. Links probably used in many different arrangements to produce more complex link models. For example, in order to create a nested link, link at layer network N can be instantiated by one or more links at layer network n-1. These arrangements refer to as component link.

This research classifies links into three classes with respect to the MEN Layer Network:

Application Link (APP): A link one of (in) the Application Layers

Ethernet Service Link (ETH): A link in Ethernet Service Link

Transport Link (TRAN): A link one of (in) the Transport Link

Probably multiple links will exist between any of subnetwork (flow domains) and access group or a pair of access groups or a pair of subnetworks (flow domains). The moment links are established and maintained at the time scale of the server layer network for example control plane provisioned links versus EMS/NMS provisioned links). They are not just limited to being provided by client layer network connection and also can be provided by a server layer network. The MEN UNI and E-NNI reference points and the relationship between link types relationship as showed in the below Figure 8 as the high level of relationship.

Figure 8: Example of MEN Reference Link Model