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Intelecommunications, apoint-to-point connection is a communications connection between twocommunication endpoints ornodes. An example is atelephone 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 apoint-to-multipoint orbroadcast connection, in which many nodes can receive information transmitted by one node. Other examples of point-to-point communications links areleased lines andmicrowave radio relay.
The term is also used incomputer networking andcomputer architecture to refer to a wire or other connection that links only two computers or circuits, as opposed to othernetwork topologies such asbuses orcrossbar switches which can connect many communications devices.
Point-to-point is sometimes abbreviated asP2P. This usage ofP2P is distinct fromP2P meaningpeer-to-peer in the context offile sharing networks or other data-sharing protocols between peers.
A traditional point-to-point data link is a communications medium with exactly two endpoints and no data orpacket 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 anRS-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 amodem to convert analog telecommunications signals into a digital data stream. When the connection uses a telecommunications provider, the connection is called adedicated,leased, orprivate line. TheARPANET used leased lines to provide point-to-point data links between itspacket-switching nodes, which were calledInterface Message Processors.
With the exception ofpassive optical networks, modernEthernet is exclusively point-to-point on thephysical layer – any cable only connects two devices. The term point-to-point telecommunications can also mean awireless data link between two fixed points. The wireless communication is typically bi-directional and eithertime-division multiple access (TDMA) orchannelized. This can be amicrowave relay link consisting of a transmitter which transmits a narrow beam of microwaves with aparabolic dish antenna to a second parabolic dish at the receiver. It also includes technologies such aslasers which transmit data modulated on a light beam. These technologies require an unobstructedline of sight between the two points and thus are limited by the visual horizon to distances of about 40 miles (64 km).[a]
In alocal network,repeater hubs orswitches 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 havingfull-duplex connections.
From theOSI model's layer perspective, both switches and repeater hubs provide point-to-point connections on thephysical layer. However, on thedata link layer, a repeater hub provides point-to-multipoint connectivity – eachframe is forwarded to all nodes – while a switch provides virtual point-to-point connections – eachunicast frame is only forwarded to the destination node.
Within manyswitched 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.
