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Metropolitan area network based on Ethernet standards

A metropolitan area Ethernet, Ethernet MAN, carrier Ethernet or metro Ethernet network is a metropolitan area network (MAN) that is based on Ethernet standards. It is commonly used to connect subscribers to a larger service network or for internet access. Businesses can also use metropolitan area Ethernet to connect their own offices to each other. An Ethernet interface is typically more economical than a synchronous digital hierarchy (SONET/SDH) or plesiochronous digital hierarchy (PDH) interface of the same bandwidth. 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 residential networks. A typical service provider's network is a collection of switches and routers connected through optical fiber. The topology could be a ring, hub and spoke (star), or full or partial mesh. The network will also have a hierarchy: core, distribution (aggregation), 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 10 Gbit/s, 40 Gbit/s, or 100 Gbit/s speeds or even possibly 400 Gbit/s to Terabit Ethernet network in the future. Ethernet on the MAN can be used as pure Ethernet, Ethernet over SDH, Ethernet over Multiprotocol Label Switching (MPLS), or Ethernet over DWDM. Ethernet based deployments with no other underlying transport are cheaper but are harder to implement in a resilient and scalable manner, which has limited its use to small scale or experimental deployments. SDH based deployments are useful when there is an existing SDH infrastructure already in place; its main shortcoming is 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.

Familiar network domains are likely to exist regardless of the transport technology chosen to implement metropolitan area networks: Access, aggregation/distribution, and core. Access devices normally exist at a customer's premises, unit, or wireless base station. This is the network that connects customer equipment, and may include optical network terminal (ONT), a residential gateway, or office router. Aggregation occurs on a distribution network such as an ODN segment. Often passive optical network, microwave or digital subscriber line technologies are employed, but some of them using point to point Ethernet over "home run" direct fibre. This part of the network includes nodes such as Multi Tenanted Unit switches, optical line terminals in an outside plant or central office cabinet, Ethernet in the first mile equipment, or provider bridges. A MAN may include the transport technologies MPLS, PBB TE and T MPLS, each with its own resiliency and management techniques. A core network often uses IP MPLS to connect different MANs together. Much of the functionality of Ethernet MANs such as virtual private lines or virtual private networks is implemented by the use of Ethernet VLAN tags that allow differentiation of each part of the network. Logical differentiation of the physical network helps to identify the rights that the traffic has and to ease the management of hosts' access rights with respect to other users and networks.

Some service providers deployed metro Ethernet networks using fixed wireless technology. These networks commonly are engineered with a majority of the network traffic using a mesh of multi point and point to point microwave links. Carriers have more recently been referred to as metro wireless in many cases. Metro Wireless providers in many cases are able to produce shorter installation times due to less permitting and procedure necessary. Many consumers now rely on this type of technology to allow Internet access in areas where local telephone companies and cable companies do not or will no longer service due to copper theft or other business reasons. Wireless is also commonly used as a true redundant path to the Internet.

In late September 2007 Verizon Business announced metro Ethernet across Asia Pacific including Australia, Singapore, Japan and Hong Kong using Nortel equipment. In late January 2009, Windstream announced it would begin offering metro Ethernet service to small and medium business customers. In May 2011, Comcast announced its own metro Ethernet services to business customers in the United States.