2.3.c Describe WAN rate-based ethernet circuits

A metropolitan -area Ethernet, Ethernet MAN, 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 the Internet. Businesses can also use Ethernet-based MAN to connect their own offices to each other.

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 cheaper but less reliable and scalable and thus are usually limited to small scale 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.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 2160-2167).  . Kindle Edition.

http://en.wikipedia.org/wiki/Metro_Ethernet