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Last mile (telecommunications)
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==Existing delivery system problems== [[File:The last mile hierarchy.svg|thumb|upright=1.7|Schematic representation of the [[tree (graph theory)|tree]] topology of retail distribution networks. The "last mile" links are represented by the fine lines at the bottom. ]] The increasing worldwide demand for rapid, low-[[Network latency|latency]] and high-volume communication of [[information]] to homes and businesses has made economical information distribution and delivery increasingly important. As demand has escalated, particularly fueled by the widespread adoption of the [[Internet]], the need for economical high-speed access by end-users located at millions of locations has ballooned as well. As requirements have changed, the existing systems and networks that were initially pressed into service for this purpose have proven to be inadequate. To date, although a number of approaches have been tried, no single clear solution to the 'last mile problem' has emerged. As expressed by [[Shannon–Hartley theorem|Shannon's equation]] for [[channel capacity|channel information capacity]], the omnipresence of [[noise]] in information systems sets a minimum [[signal-to-noise ratio]] (shortened as S/N) requirement in a channel, even when adequate [[Bandwidth (signal processing)|spectral bandwidth]] is available. Since the integral of the rate of information transfer with respect to time is information quantity, this requirement leads to a corresponding minimum [[Eb/N0|energy per bit]]. The problem of sending any given amount of information across a channel can therefore be viewed in terms of sending sufficient Information-Carrying Energy (ICE).{{citation needed|date=June 2018}} For this reason the concept of an ICE 'pipe' or 'conduit' is relevant and useful for examining existing systems. The distribution of information to a great number of widely separated end-users can be compared to the distribution of many other resources. Some familiar analogies are: *Blood distribution to a large number of [[cell (biology)|cell]]s over a system of [[veins]], [[arteries]] and [[capillaries]] *Water distribution by a [[drip irrigation]] system to individual [[plants]], including [[river]]s, [[aqueduct (watercourse)|aqueducts]], [[water mains]], etc. *Nourishment to a plant's leaves through [[root]]s, [[trunk (botany)|trunk]] and [[branches]]. All of these have in common conduits that carry a relatively small amount of a resource a short distance to a very large number of physically separated endpoints. Also common are conduits supporting more voluminous flow, which combine and carry many individual portions over much greater distances. The shorter, lower-volume conduits, which individually serve only one or a small fraction of the endpoints, may have far greater combined length than the larger capacity ones. These common attributes are shown to the right. ===Costs and efficiency=== The high-capacity conduits in these systems tend to also have in common the ability to efficiently transfer the resource over a long distance. Only a small fraction of the resource being transferred is wasted, lost, or misdirected. The same cannot necessarily be said of lower-capacity conduits. One reason has to do with the [[Economies of scale|efficiency of scale]]. Conduits that are located closer to the endpoint, or end-user, do not individually have as many users supporting them. Even though they are smaller, each has the overhead of an "installation" obtaining and maintaining a suitable path over which the resource can flow. The funding and resources supporting these smaller conduits tend to come from the immediate locale. This can have the advantage of a "small-government model". That is, the management and resources for these conduits is provided by local entities and therefore can be optimized to achieve the best solutions in the immediate environment and also to make best use of local resources. However, the lower operating efficiencies and relatively greater installation expenses, compared with the transfer capacities, can cause these smaller conduits, as a whole, to be the most expensive and difficult part of the complete distribution system. These characteristics have been displayed in the birth, growth, and funding of the Internet. The earliest inter-computer communication tended to be accomplished with direct wireline connections between individual computers. These grew into clusters of small [[local area network]]s (LAN). The [[TCP/IP]] suite of [[Internet protocol suite|protocols]] was born out of the need to connect several of these LANs together, particularly as related to common projects among the [[United States Department of Defense]], industry and some academic institutions. [[ARPANET]] came into being to further these interests. In addition to providing a way for multiple computers and users to share a common inter-LAN connection, the TCP/IP protocols provided a standardized way for dissimilar computers and operating systems to exchange information over this inter-network. The funding and support for the connections among LANs could be spread over one or even several LANs. As each new LAN, or subnet, was added, the new subnet's constituents enjoyed access to the greater network. At the same time the new subnet enabled access to any network or networks with which it was already networked. Thus the growth became a mutually inclusive or "win-win" event. ====Economies of scale==== In general, economy of scale makes an increase in capacity of a conduit less expensive as the capacity is increased. There is an overhead associated with the creation of any conduit. This overhead is not repeated as capacity is increased within the potential of the technology being utilized. As the Internet has grown in size, by some estimates doubling in the number of users every eighteen months, economy of scale has resulted in increasingly large information conduits providing the longest distance and highest capacity backbone connections. In recent years, the capacity of [[fiber-optic communication]], aided by a supporting industry, has resulted in an expansion of raw capacity, so much so that in the United States a large amount of installed fiber infrastructure is not being used because it is currently excess capacity "[[dark fiber]]". This excess backbone capacity exists in spite of the trend of increasing per-user data rates and overall quantity of data. Initially, only the inter-LAN connections were high speed. End-users used existing telephone lines and modems, which were capable of data rates of only a few hundred [[Bit rate|bit/s]]. Now almost all end users enjoy access at 100 or more times those early rates.
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