Ethernet technology, as the most widely deployed local area networking (LAN) technology, has expanded its territories across a Metropolitan Area Network (MAN) or Wide Area Network (WAN) by interconnect Ethernet LANs. Ethernet service is provided the Metro Ethernet Network (MEN) provider, who will interconnect Ethernet LANs by using a few technical solutions. Basically, at the customer side, a Customer Equipment (CE) is required to connect customer devices using standard 10Mbps/100Mbps/1Gbps/10Gbps Ethernet interfaces. On the network-facing side,various technologies can be considered as atransport platform for Ethernet traffic. Oncethe connectivity is up, the customer-ownedEthernet switches across a MAN or WAN can see eachother as if they were directly connected. Thecarrier's transport network architecture istotally transparent to end users. The Metro Ethernet Service includes edge-to-edge Ethernet connectivity via Layer 2switching and Layer 1 transport technologies.

Metro Ethernet services can be offered ona point-to-point basis or on a point-to-multipointbasis. Basically there are a few technical options to provide Metro Ethernet Services:

• Optical Ethernet Using VLAN - Thissolution simply putsEthernet MAC frames on top of Ethernet PHY over fibers. The VLANtag is then used to identify circuits inthe network.A CPE is typically deployedat a customers location, which provides a customer-facing 10/100 or GigEport that connects to the customers Ethernet devices. TheEthernet MAC frames are then carried overfiber through the Ethernet PHY. The traffic isswitched in the dedicatedmetro Ethernet networkto reach its destinationusing the VLAN tag as acircuit identifier. For thetraffic in the metro area,the metro Ethernet networkis sufficient to completethe job. For the trafficgoing to a different metro area, a SONETbasedsolution is required due to the limitationon the maximum distance the Ethernettraffic can traverse over the fiber.
• Optical Ethernet Using Martini MPLS L2 VPN - Thissolution uses Multi-protocol Label Switching (MPLS) labels instead ofVLAN tags as circuit identifiers toenhance the scalability.Martini encapsulationis adopted for carrying Ethernet MAC frames.The Martini MPLS L2 VPN solution uses twolabels (VC label and Tunnel label) to identifydifferent layered circuit segments in an MPLSnetwork.
• X.86 Ethernet-over-SONET (EoS) - The EoS solution maps Ethernet MACframes onto SONET channels throughHigh level Data Link Control (HDLC)-like framing.ACPE is typically deployed atcustomers location, which providesa customer-facing 10/100 or GigE port that connects to customer Ethernet based devices. The Ethernet MACframes are encapsulated in LAPS frame, which are then mapped onto SONETSynchronous Payload Envelope (SPE) andtransported over metro SONET rings. TheVLAN tag is used for circuit identification. Forthe traffic in the same metro area, the EoStraffic can be terminated and switched on an Ethernet/VLAN switch in the regional CO. TheEoS circuits are exchanged according to thepre-provisioned VLAN tags. For the trafficgoing to a different metro area, a SONETbasedsolution is required.
• Martini MPLS L2 VPN Over SONET - This solution uses MPLS as a transportvehicle across an IP-based multi-service core. A CPE is deployed at customers location, which provides acustomer-facing 10/100 or GigE port that connects with customers Ethernet based devices. The EthernetMAC frames are carried over the MPLS POSnetwork through Martini encapsulation. The traffic flows are capable of being switched inthe MPLS network to reach their destinations.In other words, the Martini MPLS L2 VPNsolution eliminates the need to bridge differenttransport technologies for MAN andWAN at the regional CO.
• VPLS (and HVPLS) - Virtual Private LAN Service (VPLS), also called as Ethernet VPN, is a new technology using MPLS as a transportvehicle to provide layer 2 Ethernet VPN services. It can provide both point-to-point services and point-to-multipoint services.

Metro Ethernet Network and Services: Technology Overview

Related Terms:MPLS, VPLS, Ethernet VPN, Layer 2 VPN, VLAN