Last-mile

The last mile or last kilometer is a colloquial phrase widely used in the telecommunications, cable television and internet industries to refer to the final leg of the telecommunications networks that deliver telecommunication services to retail end-users (customers). More specifically, the last mile refers to the portion of the telecommunications network chain that physically reaches the end-user's premises. Examples are the copper wire subscriber lines connecting landline telephones to the local telephone exchange; coaxial cable service drops carrying cable television signals from utility poles to subscribers' homes, and cell towers linking local cell phones to the cellular network. The word "mile" is used metaphorically; the length of the last mile link may be more or less than a mile. Because the last mile of a network to the user is conversely the first mile from the user's premises to the outside world when the user is sending data (sending an email, for example), the term first mile is also alternately used.

The last mile is typically the speed bottleneck in communication networks; its bandwidth effectively limits the bandwidth of data that can be delivered to the customer. This is because retail telecommunication networks have the topology of "trees", with relatively few high capacity "trunk" communication channels branching out to feed many final mile "leaves". The final mile links, being the most numerous and thus most expensive part of the system, as well as having to interface with a wide variety of user equipment, are the most difficult to upgrade to new technology. For example, telephone trunklines that carry phone calls between switching centers are made of modern optical fiber, but the last mile is typically twisted pair wires, a technology which has essentially remained unchanged for over a century since the original laying of copper phone cables.

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