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All about Physical Link: Introduction to Metro Ethernet

Today I am going to talk about Metro Ethernet. There are lot of people who wants to understand what actually metro ethernet services are and why we are taking these kinds of services. We will come up with your queries one by one and will also describe in this article why service providers are providing metro ethernet services to the customers.

Background about Metro Ethernets
Metro Ethernet services are now offered by a wide range of service providers. Some providers have extended Ethernet services beyond the metropolitan area and across the wide area. Thousands of subscribers already use Ethernet services and their numbers are growing rapidly. These subscribers have been attracted by the benefits of Ethernet services.

Ethernet services are provided over a standard, widely available and well-understood Ethernet interface. Virtually all networking equipment and hosts connect to the network using Ethernet so using an Ethernet service to interconnect such devices simplifies network operations, administration, management and provisioning.

Fig 1.1- Metro Ethernet Deployment Scenarios


What is the purpose of the Metro Ethernet ?
Service providers use Metro Ethernet to provide Layer 2 Ethernet connections between customer sites in metro area networks. Driven by its relative simplicity, high bandwidth, and low-cost switches, Ethernet has become the transport technology of choice in metro area networks. 

There are numerous applications that require pure Layer 2 connectivity in the metro area network (MAN) for providing simple point-to-point, point-to-multipoint, or multipoint-to-multipoint services with a relatively low number of customer sites. 

What is the purpose of the use in MPLS connectivity ?
However, Ethernet limitations become apparent in large MANs with thousands of access nodes. In this case, service providers are more likely to offer Layer 3 Virtual Private Network (L3 VPN) services based on multiprotocol label switch (MPLS) transport. 

When interconnecting hundreds or thousands of customer sites, this approach gives more flexibility, better scale, and ease of OAM. One example is the number of LTE mobile backhaul networks that are based on end-to-end Layer 3 connectivity provided in the MAN by means of Layer 3 VPN services. 

This solution comes at higher cost per port in comparison to Layer 2 services that are based on Ethernet switches, but it saves on operational expenses (OPEX) because of the ease of network operations. 


Fig 1.2- MPLS Scenario on Metro Ethernet


What kind of MPLS connectivity we can do with the use of Metro Ethernet ?

MPLS services, such as Ethernet pseudowire, L2 VPNs, VPLS, H-VPLS, or EVPN, can be used to enable any type of Layer 2 Ethernet virtual connections (EVCs). The differentiators of this solution are higher network service flexibility and higher scaling of the MAN where Metro 

Ethernet services may span multiple network segments and be seamlessly terminated at any point of the network or cloud. 

Typical carrier portfolios now include mixed Layer 2 and Layer 3 services in the MAN. The modern MAN has not only media to provide Layer 2 connectivity, but also as a cloud of available network resources where both Layer 2 and Layer 3 services complement each other. 

In this context, Layer 2 E-Line can be used to backhaul traffic from the customer site to the Layer 3 service attached point, which may be located at the carrier network for an application, either as a physical or virtual service node. 

Other features of Metro Ethernet ?
Ethernet services allow subscribers to network their business in ways that are either more complex or impossible with alternative services. For example, a single Ethernet service interface can connect multiple enterprise locations for their Intranet VPNs, connect business partners or suppliers via Extranet VPNs and provide a high speed Internet connection to an Internet Service Provider. 

With managed Ethernet services, subscribers are also able to add or change bandwidth in minutes instead of days or weeks when using other access network services. 

What are the standard using in the Metro Ethernet Services ?
Well let's talk about UNI, NNI and EVC standards used in the Metro Ethernet services

User-Network Interface (UNI): Service Provider uses UNI interface and now the question is what is this UNI interface is actually. The UNI is a physical Ethernet port on the service provider side of the network along with predefined set of parameters to provide data, control and management traffic exchange with the end-customer CPE device. 

The customer CPE device can be a Layer 2 Ethernet switch, Layer 3 routing node, NodeB or eNodeB (LTE), Evolved Packet Core (EPC) router, mobile packet core (MPC), etc. Configuration of the UNI may include settings associated with the Ethernet services infrastructure and the transport network infrastructure. 

External Network-to-Network Interface (E-NNI): So you guys are able to understand the UNI interfaces as of now, Lets talk about the NNI interfaces which service providers are also using as a standard connectivity. 

Fig 1.3- ENNI Setup

The full definition of the E-NNI is given by MEF 4. In general, E-NNI is represented by the physical Ethernet port on the service provider access node that is used to interconnect two Ethernet MANs of two different service providers.

We are also using E-NNI as a reference point for the interconnection of Layer 2 MAN service with Layer 3 service nodes—the provider edge router (PE), a broadband network gateway (BNG), vertical handover (VHO), etc in the provider network. 

Ethernet Virtual Connection (EVC):After UNI and NNI, now lets have a quick note on EVC. So EVC is the architecture construct that supports the association of UNI reference points for the purpose of delivering an Ethernet flow between subscriber sites across the MAN. 

There can be one or more subscriber flows mapped to a particular EVC; that is, there may be more subscriber flows identified by the flow classification rules at the ingress point to a network than EVCs. The mapping of Ethernet flows to EVCs is service specific and specified in the MEF Ethernet Service Model specification 

Fig 1.4- EVC Setup 


Metro Ethernet Services can support a range of applications more easily, efficiently and cost-effectively than other network services. Using standard Ethernet interfaces, subscribers can set up secure, private Ethernet Virtual Connections across a Metropolitan Area, or even a Wide Area, to connect their sites together and connect to business partners, suppliers and the Internet. 

Using point-to-point E-Line Services and multipoint E-LAN Services, subscribers can connect to one site or many. With service options such as Service Multiplexing, subscribers can use a single UNI to support multiple connections. 

Additionally, with many Ethernet services, subscribers can buy just the bandwidth they need today, knowing that they can quickly and easily add bandwidth and set up new connections.


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