Metro Ethernet

runicode 2008. 3. 8. 05:06
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A Metro Ethernet is a computer network based on the Ethernet standard and which covers a metropolitan area. It is commonly used as a metropolitan access network to connect subscribers and businesses to a Wide Area Network, such as the Internet. Large businesses can also use Metro Ethernet to connect branch offices to their Intranets.

Ethernet has been a well known technology for decades. An Ethernet interface is much less expensive than a SDH or PDH interface of the same bandwidth. Ethernet also supports high bandwidths with fine granularity, which is not available with traditional SDH connections. Another distinct advantage of an Ethernet-based access network is that it can be easily connected to the customer network, due to the prevalent use of Ethernet in corporate and, more recently, residential networks. Therefore, bringing Ethernet in to the Metropolitan Area Network (MAN) introduces a lot of advantages to both the service provider and the customer (corporate and residential).

Metro Ethernet systemA typical service provider Metro Ethernet network is a collection of Layer 2 or 3 switches or routers connected through optical fiber. 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/MPLS backbone, but may migrate to newer forms of Ethernet Transport in the form of 10G or 100G speeds.

Ethernet on the MAN can be used as pure Ethernet, Ethernet over SDH, Ethernet over MPLS or Ethernet over DWDM. Pure Ethernet-based deployments are cheap but less reliable and scalable, and thus are usually limited to small scale or experimental deployments. SDH-based deployments are useful when there is an existing SDH infrastructure already in place, its main shortcoming being the loss of flexibility in bandwidth management due to the rigid hierarchy imposed by the SDH network. MPLS based deployments are costly but highly reliable and scalable, and are typically used by large service providers.