What is a Metro Ethernet Service?

Metro Ethernet is a computer network based on the Ethernet standard and which covers a metropolitan area. It is commonly used as a metropolitan and first mile access network to connect subscribers and businesses to a Wide Area Network (WAN), such as the internet. As an Ethernet first mile access technology, large businesses can use a MetroEthernet service to connect branch offices to their intranets or to run real-time business applications.

Ethernet has been a well known technology for decades but more recently it has become a highly demanded for first mile access. An Ethernet interface is much less expensive than a SONET/SDH or PDH interface of the same bandwidth. Metro Ethernet also supports high bandwidths with fine granularity, which is not available with traditional SDH connections.

Another distinct advantage of a Metro Ethernet-based access network is that it can be easily connected to a customer network. This is due to the prevalent use of Ethernet in corporate networks. Therefore, bringing MetroEthernet in to the Metropolitan Area Network (MAN) as well as using it as Ethernet first mile access introduces a number of advantages to both the service provider and the corporate.

A typical service provider Metro Ethernet network is a collection of Layer 2 and/or 3 switches and/or routers connected through optical fiber. The topology could be a ring, hub-and-spoke (star), or full or partial mesh. The Metro Ethernet network will also have a hierarchy: core, distribution aggregation and access. The core in most cases is an existing IP backbone, but may migrate to newer forms of Ethernet Transport in the form of 10Gb or 100Gb speeds.

Metro Ethernet service technology is fast growing in popularity with HKBN building the largest Metro Ethernet IP network in the world in June 2002, covering 1.2 million homes. In September 2007 Verizon Business announced that it is to implement a MetroEthernet service across Asia-Pacific including Australia, Singapore, Japan and Hong Kong using Nortel equipment.

The Technology of Metro Ethernet Service

For the typical service provider, a Metro Ethernet network is a collection of Layer 2 or 3 switches or routers connected through optical fibre. The topology could be a ring, hub-and-spoke (star), full mesh or partial mesh. The network will also have a hierarchy; core, distribution and access. The core in most cases is an existing IP backbone, but may migrate to newer forms of Ethernet Transport in the form of 10Gbps or 100Gbps speeds.

Pure Ethernet MAN's

A pure Ethernet MAN uses only layer 2 switches for all its internal structure. This allows for a very simple and cheap design and also for a relatively simple initial configuration. The original Ethernet technology wasn't well suited for service provider applications; as a shared-media network, it was impossible to keep traffic isolated, which made implementation of private circuits impossible.

Ethernet MANs became feasible in the late 90's due to the development of new techniques to allow transparent tunnelling of traffic through the use of Virtual LANs as "point to point" or "multipoint to multipoint" circuits. Combined with new features such as VLAN Stacking (also known as VLAN Tunnelling), and VLAN Translation, it became possible to isolate the customer's traffic from each other and from the core network internal signalling traffic.