RS-485: Imported from Wikipedia (overwrite)

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Imported from Wikipedia (overwrite)

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{{Short description|Communication connection between two nodes or endpoints}}
{{Refimprove|date=December 2006}}
In [[telecommunications]], a '''point-to-point''' connection is a communications connection between two [[communication endpoint]]s or [[Node (networking)|nodes]]. An example is a [[telephone call]], in which one telephone is connected with one other, and what is said by one caller can only be heard by the other. This is contrasted with a ''[[point-to-multipoint]]'' or ''[[Broadcasting (networking)|broadcast]]'' connection, in which many nodes can receive information transmitted by one node. Other examples of point-to-point communications links are [[leased line]]s and [[microwave radio relay]].

The term is also used in [[computer networking]] and [[computer architecture]] to refer to a wire or other connection that links only two computers or circuits, as opposed to other [[network topologies]] such as [[computer bus|buses]] or [[crossbar switch]]es which can connect many communications devices.

''Point-to-point'' is sometimes abbreviated as ''P2P''. This usage of ''P2P'' is distinct from ''P2P'' meaning ''[[peer-to-peer]]'' in the context of [[file sharing]] networks or other data-sharing protocols between peers.

==Basic data link==
A traditional point-to-point data link is a communications medium with exactly two endpoints and no data or [[Packet (information technology)|packet]] formatting. The host computers at either end take full responsibility for formatting the data transmitted between them. The connection between the computer and the communications medium was generally implemented through an [[RS-232]] or similar interface. Computers in close proximity may be connected by wires directly between their interface cards.

When connected at a distance, each endpoint would be fitted with a [[modem]] to convert analog telecommunications signals into a digital data stream. When the connection uses a telecommunications provider, the connection is called a [[dedicated line|dedicated]], [[leased line|leased]], or [[private line]]. The [[ARPANET]] used leased lines to provide point-to-point data links between its [[packet-switching]] nodes, which were called [[Interface Message Processor]]s.

==Modern links==
[[File:CableFree_MMW_Link_installed_in_UAE.jpg|thumb|right|A 1 Gbit/s point-to-point [[millimeter-wave]] link installed in the [[UAE]]]]
[[File:Locale_RS6_RADWIN-point-to-point-wireless-Huntington-Beach.jpg|thumb|A point-to-point wireless unit with a built-in antenna at [[Huntington Beach, California]]]]

With the exception of [[passive optical network]]s, modern [[Ethernet]] is exclusively point-to-point on the [[physical layer]] – any cable only connects two devices. The term point-to-point telecommunications can also mean a [[wireless networking|wireless]] data link between two fixed points. The wireless communication is typically bi-directional and either ''[[time-division multiple access]]'' (TDMA) or [[Channelization (telecommunications)|channelized]]. This can be a [[microwave relay]] link consisting of a transmitter which transmits a narrow beam of microwaves with a [[parabolic antenna|parabolic dish]] antenna to a second parabolic dish at the receiver. It also includes technologies such as [[laser]]s which transmit data modulated on a light beam. These technologies require an unobstructed [[line-of-sight propagation|line of sight]] between the two points and thus are limited by the visual horizon to distances of about {{convert|40|mi|km|abbr=}}.{{efn|The [[Telecommunications Industry Association]]'s engineering committees develop U.S. standards for point-to-point communications and related cellular tower structures.<ref>{{cite web|url=http://www.tiaonline.org/standards/committees/committee.cfm?comm=tr-14|title=TR-14 {{!}} Structural Standards for Communication and Small Wind Turbine Support Structures|work=Telecommunications Industry Association|access-date=2011-11-20|archive-url=https://web.archive.org/web/20140107033301/http://www.tiaonline.org/standards/committees/committee.cfm?comm=tr-14|archive-date=2014-01-07|url-status=dead}}</ref> Online tools help users find if they have such line of sight.<ref>{{cite web |title= PtP Estimator Overview |publisher= AlphiMAX |url= http://www.alphimax.com/ptp |access-date= August 29, 2011 }}</ref>}}

==Networking==
In a [[local network]], [[repeater hub]]s or [[network switch|switches]] provide basic connectivity. A hub provides a point-to-multipoint (or simply multipoint) circuit in which all connected client nodes share the network bandwidth. A switch on the other hand provides a series of point-to-point circuits, via microsegmentation, which allows each client node to have a dedicated circuit and the added advantage of having [[full-duplex]] connections.

From the [[OSI model]]'s layer perspective, both switches and repeater hubs provide point-to-point connections on the [[physical layer]]. However, on the [[data link layer]], a repeater hub provides point-to-multipoint connectivity – each [[frame (networking)|frame]] is forwarded to all nodes – while a switch provides virtual point-to-point connections – each [[unicast]] frame is only forwarded to the destination node.

Within many [[Circuit switching|switched telecommunications systems]], it is possible to establish a permanent circuit. One example might be a telephone in the lobby of a public building, which is programmed to ring only the number of a telephone dispatcher. "Nailing down" a switched connection saves the cost of running a physical circuit between the two points. The resources in such a connection can be released when no longer needed, for example, a television circuit from a parade route back to the studio.

==See also==
*[[IP shuffling]]
*[[Point-to-multipoint communication]]

==Notes==
{{notelist}}

==References==
{{Reflist}}
{{Telecommunications}}

[[Category:Network topology]]
[[Category:Telecommunication services]]

Point-to-point (telecommunications) - Revision history

RS-485: Imported from Wikipedia (overwrite)