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In telecommunications, point-to-multipoint communication is communication which is accomplished via a distinct type of one-to-many connection, providing multiple paths from a single location to multiple locations.〔 〕 ''Point-to-multipoint'' is often abbreviated as P2MP, PTMP, or PMP. Point-to-multipoint telecommunications is most typically (2003) used in wireless Internet and IP telephony via gigahertz radio frequencies. P2MP systems have been designed both as single and bi-directional systems. A central antenna or antenna array broadcasts to several receiving antennas and the system uses a form of time-division multiplexing to allow for the back-channel traffic. == Modern point-to-multipoint links == In contemporary usage, the term point-to-multipoint wireless communications relates to fixed wireless data communications for Internet or voice over IP via radio or microwave frequencies in the gigahertz range. Point to Multipoint is the most popular approach for wireless communications that have a large number of nodes, end destinations or end users. Point to Multipoint generally assumes there is a central Base Station to which remote Subscriber Units or Customer Premises Equipment, CPE (a term that was originally used in the wired telephone industry) are connected over the wireless medium. Connections between the Base Station and Subscriber Units can be either Line of Sight or for lower-frequency radio systems Non-Line-of-Sight where link budgets permit. Generally, lower frequencies can offer non-Line-of Sight connections. Various software planning tools can be used to determine feasibility of potential connections using topographic data as well as link budget simulation. Often the point to multipoint links are installed to reduce the cost of infrastructure and increase the number of CPE's and connectivity.〔 Point to Multipoint wireless networks employing directional antennas are affected by the hidden node problem (also called hidden terminal) in case they employ a CSMA/CA medium access control protocol. The negative impact of the hidden node problem can be mitigated using a TDMA based protocol or a polling protocol rather than the CSMA/CA protocol.〔(【引用サイトリンク】url=http://www.fluidmesh.com/point-to-multipoint-wireless/ )〕 The telecommunications signal in an Point to Multipoint system is typically bi-directional, either time division multiple access (TDMA) or channelized. Systems using Frequency Division Duplexing (FDD) offer full duplex connections between base station and remote sites, and Time Division Duplex (TDD) systems offer half duplex connections. Point to Multipoint systems can be implemented in Licensed, Semi-licensed or Unlicensed frequency bands depending on the specific application. Point-to-point and point-to-multipoint links are very popular in the wireless industry and when paired with other high-capacity wireless links or technologies such as Free Space Optics (FSO) can be referred to as backhaul. The Base Station may have a single Omnidirectional antenna or multiple Sector Antennas which is often used to increase both range and capacity. 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「Point-to-multipoint communication」の詳細全文を読む スポンサード リンク
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