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Analysis: Carrier Ethernet: Page 5 of 11

Carrier Ethernet is generally sold in one of two configurations: E-Line is a point-to-point Ethernet link, while E-LAN provides a multipoint mesh. In both cases, connections are logically terminated using a UNI (Universal Network Interface). Multiple UNIs can be attached to one physical termination point, allowing a single WAN link to support multiple Carrier Ethernet services simultaneously.

E-Line is ideal in situations were high speed, low latency and data privacy are high priorities, making it a best bet for data-center-to-data-center connections and disaster recovery. E-Line is similar to frame relay in that each E-Line connection forms a Ethernet Virtual Circuit over the shared Ethernet network.

E-LAN is where the power of Carrier Ethernet really takes off. Unlike conventional WAN technologies like TDM, frame relay or Sonet, E-LAN Carrier Ethernet turns the WAN into a mesh. An E-LAN can simply switch packets where needed, or 802.1Q tags can direct frames to specific locations, just as on the LAN. The carrier is responsible for delivering frames to their respective destinations.

An interesting side benefit of E-LAN is that you can flatten your network topology and do away with edge routers altogether, opting to switch traffic from place to place. If your WAN topology already includes edge routers--and whose doesn't--you can continue to use them, but doing so defeats one of the design benefits of Carrier Ethernet. However, flattening does require that the carrier intelligently handle broadcast traffic, lest it overwhelm your network.

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