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In telecommunications and computer networks, a virtual circuit (VC), synonymous to virtual connection and virtual channel, is a connection oriented communication service that is delivered by means of packet mode communication. After a connection or virtual circuit is established between two nodes or application processes, a bit stream or byte stream may be delivered between the nodes. A virtual circuit protocol hides the division into segments, packets or frames from higher level protocols. Image File history File links Merge-arrows. ... A connection-oriented networking protocol is one which identifies traffic flows by some connection identifier rather than by explicitly listing source and destination addresses. ... Telecommunication involves the transmission of signals over a distance for the purpose of communication. ... A computer network is a system for communication among two or more computers. ... In telecommunications, a virtual channel is a channel designation which differs from the actual radio channel or frequency which the signal travels. ... A connection-oriented networking protocol is one which identifies traffic flows by some connection identifier rather than by explicitly listing source and destination addresses. ... Wikipedia does not yet have an article with this exact name. ... A bitstream or bit stream is a time series of bits. ... A byte stream is an abstraction used in computer science to describe a particular kind of communication channel between two entities. ...

Virtual circuit communication resembles circuit switching, since both are connection oriented, meaning that in both cases data is delivered in correct order, and signalling overhead is required during a connection establishment phase. However, circuit switching provides constant bit rate and latency, while these may vary in a virtual circuit service due to reasons such as: In telecommunications, a circuit switching network is one that establishes a dedicated circuit (or channel) between nodes and terminals before the users may communicate. ...

• varying packet queue lengths in the network nodes,
• varying bit rate generated by the application,
• varying load from other users sharing the same network resources by means of statistical multiplexing, etc.

Many virtual circuit protocols, but not all, provide reliable communication service, by means of data retransmissions due to error detection and automatic repeat request (ARQ). Statistical multiplexing is similar to time-division multiplexing (TDM), except that, rather than arbitrarily assigning a time slot to each signal, each signal is assigned a slot according to priority and need. ... In computer networking, a reliable protocol is one that ensures data arrival via some internal method, as opposed to an unreliable protocol, which does not guarantee that all the data will arrive intact (or indeed, at all). ... In computer science and information theory, error correction consists of using methods to detect and/or correct errors in the transmission or storage of data by the use of some amount of redundant data and (in the case of transmission) the selective retransmission of incorrect segments of the data. ... Automatic Repeat-reQuest (ARQ) is an error control method for data transmission which makes use of acknowledgments and timeouts to achieve reliable data transmission. ...

Layer 4 virtual circuits

Connection oriented transport layer datalink protocols such as TCP^[1][2] may rely on a connectionless packet switching network layer protocol such as IP, where different packets may be routed over different paths, and thus be delivered out of order. However, a virtual circuit^[2][3][4] is possible since TCP includes segment numbering and reordering on the receiver side to prevent out-of-order delivery. In computing and telecommunications, the transport layer is the second highest layer in the four and five layer TCP/IP reference models, where it responds to service requests from the application layer and issues service requests to the Internet layer. ... The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. ... The Internet Protocol (IP) is a data-oriented protocol used for communicating data across a packet-switched internetwork. ...

Layer 2/3 virtual circuits

Network layer and datalink layer virtual circuit protocols are based on connection oriented packet switching, meaning that data is always delivered along the same network path, i.e. through the same nodes. Advantages with this over connectionless packet switching are: The network layer is third layer out of seven in OSI model and it is the third layer out of five in TCP/IP model. ... The data link layer is layer two of the seven-layer OSI model as well as of the five-layer TCP/IP reference model. ... In computer networking and telecommunications, packet switching is a communications paradigm in which packets (messages or fragments of messages) are individually routed between nodes, with no previously established communication path. ...

• Bandwidth reservation during the connection establishment phase is supported, making guaranteed Quality of Service (QoS) possible. For example, a constant bit rate QoS class may be provided, resulting in emulation of circuit switching.
• Less overhead is required, since the packets are not routed individually and complete addressing information is not provided in the header of each data packet. Only a small virtual channel identifier (VCI) is required in each packet. Routing information is only transferred to the network nodes during the connection establishment phase.
• The network nodes are faster and have higher capacity in theory, since they are switches that only perform routing during the connection establishment phase, while connectionless network nodes are routers that perform routing for each packet individually. Switching only involves looking up the virtual channel identifier in a table rather than analyzing a complete address. Switches can easily be implemented in ASIC hardware, while routing is more complex and require software implementation. However, due to the large market of IP routers, and because advanced IP routers support layer 3 switching, modern IP routers may today be faster than switches for connection oriented protocols.

In the fields of packet-switched networks and computer networking, the traffic engineering term Quality of Service, abbreviated QoS, refers to resource reservation control mechanisms. ... Constant bit rate (CBR) is a term used in telecommunications, relating to the quality of service. ... In telecommunications, a circuit switching network is one that establishes a dedicated circuit (or channel) between nodes and terminals before the users may communicate. ... A Virtual Channel Identifier (VCI) is a unique identifier which indicates a particular virtual circuit on a network. ... This article does not cite any references or sources. ... Cisco Systems Gigabit Switch Router. ...

Examples of protocols that provide virtual circuits

Examples of transport layer protocols that provide a virtual circuit:

• Transmission Control Protocol (TCP), where a reliable virtual circuit is established on top of the underlying unreliable and connectionless IP protocol. The virtual circuit is identified by the source and destination network socket address pair, i.e. the sender and receiver IP address and port number. Guaranteed QoS is not provided.
• SCTP.

Examples of network layer and datalink layer virtual circuit protocols, where data always is delivered over the same path: The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite. ... An Internet socket (or commonly, a socket or network socket), is a communication end-point unique to a machine communicating on an Internet Protocol-based network, such as the Internet. ... In the field of computer networking, the IETF Signaling Transport (SIGTRAN) working group defined the Stream Control Transmission Protocol (SCTP) as a transport layer protocol in 2002. ...

• X.25, where the VC is identified by a virtual channel identifier (VCI). X.25 provides reliable node-to-node communication and guaranteed QoS.
• Frame relay, where the VC is identified by a VCI. Frame relay is unreliable, but may provide guaranteed QoS.
• Asynchronous Transfer Mode (ATM), where the circuit is identified by a virtual path identifier (VPI) and virtual channel identifier (VCI) pair. ATM is unreliable, but may provide guaranteed QoS.
• General Packet Radio Service (GPRS)
• Multiprotocol label switching (MPLS), which can be used for IP over virtual circuits. Each circuit is identified by a label. MPLS is unreliable, but provides eight different QoS classes.

X.25 is an ITU-T standard protocol suite for wide area networks using leased lines, the phone or ISDN system as the networking hardware. ... A Virtual Channel Identifier (VCI) is a unique identifier which indicates a particular virtual circuit on a network. ... In the context of computer networking, frame relay consists of an efficient data transmission technique used to send digital information quickly and cheaply in a relay of frames to one or many destinations from one or many end-points. ... Asynchronous Transfer Mode (ATM) is a cell relay, packet switching network and data link layer protocol which encodes data traffic into small (53 bytes; 48 bytes of data and 5 bytes of header information) fixed-sized cells. ... Virtual Path Identifier refers to an 8-bit (user to network packets) or 12-bit (network-network packets) field within the header of an Asynchronous Transfer Mode packet. ... A Virtual Channel Identifier (VCI) is a unique identifier which indicates a particular virtual circuit on a network. ... General Packet Radio Service (GPRS) is a Mobile Data Service available to users of Global System for Mobile Communications (GSM) and IS-136 mobile phones. ... In computer networking and telecommunications, Multi Protocol Label Switching (MPLS) is a data-carrying mechanism that belongs to the family of packet-switched networks. ...

Permanent and switched virtual circuits in ATM, frame relay, and X.25

Switched virtual circuits (SVCs) are generally set up on a per-call basis and are disconnected when the call is terminated; however, a permanent virtual circuit (PVC) can be established as an option to provide a dedicated circuit link between two facilities. PVC configuration is usually preconfigured by the service provider. Unlike SVCs, PVC are usually very seldom broken/disconnected. Look up call in Wiktionary, the free dictionary. ... A leased line is a (usually) symmetric telecommunications line connecting two locations together. ... This article is about a telecommunication term. ...

A switched virtual circuit (SVC) is a virtual circuit that is dynamically established on demand and is torn down when transmission is complete, for example after a phone call or a file download. SVCs are used in situations where data transmission is sporadic and/or not always between the same DTE endpoints. DTE may refer to: data terminal equipment, a term in computer science DTE Energy, a power company based in Detroit, MI Dithioerythritol, a chemical compound with two reducing SH-groups Down to Earth, a common abbreviation used on social networking websites, i. ...

A permanent virtual circuit (PVC) is a virtual circuit established for repeated/continuous use between the same data terminal equipments (DTE). In a PVC, the long-term association is identical to the data transfer phase of a virtual call. Permanent virtual circuits eliminate the need for repeated call set-up and clearing. For other uses, see Data (disambiguation). ... In the context of telecommunications, a terminal is a device which is capable of communicating over a line. ... DTE may refer to: data terminal equipment, a term in computer science DTE Energy, a power company based in Detroit, MI Dithioerythritol, a chemical compound with two reducing SH-groups Down to Earth, a common abbreviation used on social networking websites, i. ... Did you mean? decal Population transfer Manhattan Transfer List of Latin words with English derivatives Transfer (movie) Electron transfer Fare transfer A technique in propaganda This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... This article is about a portion of a periodic process. ... Clearing, in telecommunications means: A sequence of events used to disconnect a call and return to the ready state. ...

Frame relay is typically used to provide PVCs. ATM provides both switched virtual connections and permanent virtual connections, as they are called in ATM terminology. X.25 provides both SVCs and PVCs, although not all X.25 service providers or DTE implementations support PVCs as their use was much less common than SVCs. In the context of computer networking, frame relay consists of an efficient data transmission technique used to send digital information quickly and cheaply in a relay of frames to one or many destinations from one or many end-points. ... Asynchronous Transfer Mode (ATM) is a cell relay, packet switching network and data link layer protocol which encodes data traffic into small (53 bytes; 48 bytes of data and 5 bytes of header information) fixed-sized cells. ... X.25 is an ITU-T standard protocol suite for wide area networks using leased lines, the phone or ISDN system as the networking hardware. ...

References

See also

• DLCI