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The last mile or last kilometer is a widely accepted phrase used in the telecommunications, cable television and internet industries to refer to the final leg of the telecommunications networks delivery components and mechanisms to retail end-users (customers). More specifically, the last mile is the common colloquialism referring to that portion of the telecommunications network chain that physically reaches the end-user's premises. Examples are the copper wire subscriber lines connecting 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 - not literally: 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 (for example, sending an email), 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, as the most numerous and thus most expensive part of the system, 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, typically twisted pair, telephone wiring that provides service to customer premises, essentially has remained unchanged for over a century, since the original laying of copper phone cables. To resolve, or at least mitigate, the problems involved with attempting to provide enhanced services over the last mile, some firms have been mixing networks for decades. One example is fixed wireless access, where a wireless network is used instead of wires to connect a stationary terminal to the wireline network. Various solutions are being developed which are seen as an alternative to the last mile of standard incumbent local exchange carriers. These include WiMAX and broadband over power lines applications. ==Business last mile== Connectivity from the local telephone exchanges to the customer premises is also called the last mile. In many countries this is often an ISDN30 connection delivered through either a copper or fibre cable. This ISDN30 can carry 30 simultaneous telephone calls and many direct dial telephone numbers. When leaving the telephone exchange, the ISDN30 cable can be buried in the ground, usually in ducting, at very little depth. This makes any business telephone lines vulnerable to being dug up during streetworks, liable to flooding during heavy storms, and effectively subject to general wear and tear due to all manner of natural hazards. Loss, therefore, of the 'last mile' link, means the non-delivery of calls, and other data, to the business affected. Any business with ISDN30 type connectivity must anticipate such failure in its business continuity planning. There are many options, as documented in customer proprietary network information: *"Dual parenting" is where the telephone carrier provides the same numbers from two different telephone exchanges. If the cable is damaged from one telephone exchange to the customer premises most of the calls can be delivered from the surviving route to the customer. *"Diverse routing" is where the carrier can provide more than one route to supply ISDN30 connectivity from the exchange, or exchanges, (as in dual parenting), but they may share underground ducting and cabinets. *"Separacy" is where the carrier can provide more than one route to bring ISDN30 connectivity from the exchange, or exchanges, (as in dual parenting), but they may not share underground ducting and cabinets, and therefore should be absolutely separate from the telephone exchange to the customer premises. *"Exchange-based solutions" is where a specialist company working in association with the carriers offers as an enhancement the ability to divert ISDN30 connectivity upon failure to any other number or group of numbers. Carrier diversions are usually limited to all of the ISDN30 direct dial telephone numbers being delivered to one single number. *"Non-exchange-based diversion services" is where a specialist company working in association with the carrier offers an enhancement to the ability to divert ISDN30 connectivity in case of failure to any other number or group of numbers. Carrier diversions are usually limited to all of the ISDN30 direct dial telephone numbers being delivered to one single number. In the UK Teamphone offers this service in association with British Telecom. By not being in the exchanges, the Teamphone version offers an 'all or nothing' diversion service if required, but does not offer voice recording of calls. *"Ported number services" is where customers numbers can be ported to a specialist company which points the numbers to the ISDN30 direct dial telephone numbers during business as usual, and delivers them to alternative numbers during a business continuity need. These are generally carrier-independent and there are a number of companies offering such solutions in the UK and AirNorth Communications in the United States. *"Hosted numbers" is where the carriers or specialist companies can host the customer's numbers within their own or the carrier's networks and deliver calls over an IP network to the customer's sites. When a diversion service is required, the calls can be routed to alternative numbers. *"Inbound numbers", or "08 type services", is where the carriers or specialist companies can offer 08/05/03 prefixed numbers to the ISDN30 direct dial telephone numbers and can point them to alternative numbers in the event of a diversion requirement. Both carriers and specialist companies offer this type of service in the UK. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「last mile」の詳細全文を読む スポンサード リンク
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