Connection-oriented communication is a network communication mode in

telecommunication Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that ...

s and computer networking, where a

communication session In computer science and networking in particular, a session is a time-delimited two-way link, a practical (relatively high) layer in the tcp/ip protocol enabling interactive expression and information exchange between two or more communication d ...

or a semi-permanent connection is established before any useful data can be transferred. The established connection ensures that data is delivered in the correct order to the upper communication layer. The alternative to connection-oriented transmission is

connectionless communication Connectionless communication, often referred to as CL-mode communication,Information Processing Systems - Open Systems Interconnection, "Transport Service Definition - Addendum 1: Connectionless-mode Transmission", International Organization for ...

, for example the

datagram A datagram is a basic transfer unit associated with a packet-switched network. Datagrams are typically structured in header and payload sections. Datagrams provide a connectionless communication service across a packet-switched network. The deliv ...

mode communication used by

Internet Protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. ...

(IP) and

User Datagram Protocol In computer networking, the User Datagram Protocol (UDP) is one of the core communication protocols of the Internet protocol suite used to send messages (transported as datagrams in packets) to other hosts on an Internet Protocol (IP) netwo ...

, where data may be delivered out of order, since different

network packet In telecommunications and computer networking, a network packet is a formatted unit of data carried by a packet-switched network. A packet consists of control information and user data; the latter is also known as the ''payload''. Control inform ...

s are routed independently and may be delivered over different paths. Connection-oriented communication may be implemented with a

circuit switched Circuit switching is a method of implementing a telecommunications network in which two network nodes establish a dedicated communications channel ( circuit) through the network before the nodes may communicate. The circuit guarantees the full ...

connection, or a packet-mode virtual circuit connection. In the latter case, it may use either a transport layer virtual circuit protocol such as the TCP protocol, allowing data to be delivered in order. Although the lower-layer switching is connectionless, or it may be a

data link layer The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer p ...

network layer In the seven-layer OSI model of computer networking, the network layer is layer 3. The network layer is responsible for packet forwarding including routing through intermediate routers. Functions The network layer provides the means of tran ...

switching mode, where all data packets belonging to the same traffic stream are delivered over the same path, and traffic flows are identified by some ''connection identifier'' reducing the overhead of routing decisions on a packet-by-packet basis for the network. Connection-oriented protocol services are often, but not always, '' reliable'' network services that provide acknowledgment after successful delivery and

automatic repeat request Automatic repeat request (ARQ), also known as automatic repeat query, is an error-control method for data transmission that uses acknowledgements (messages sent by the receiver indicating that it has correctly received a packet) and timeouts ...

functions in case of missing or corrupted data.

Asynchronous Transfer Mode Asynchronous Transfer Mode (ATM) is a telecommunications standard defined by American National Standards Institute (ANSI) and ITU-T (formerly CCITT) for digital transmission of multiple types of traffic. ATM was developed to meet the needs of ...

, Frame Relay and MPLS are examples of a connection-oriented, unreliable protocol.

SMTP The Simple Mail Transfer Protocol (SMTP) is an Internet standard communication protocol for electronic mail transmission. Mail servers and other message transfer agents use SMTP to send and receive mail messages. User-level email clients ty ...

is an example of a connection-oriented protocol in which if a message is not delivered, an error report is sent to the sender which makes SMTP a reliable protocol. Because they can keep track of a conversation, connection-oriented protocols are sometimes described as stateful.

Circuit switching

Circuit switched Circuit switching is a method of implementing a telecommunications network in which two network nodes establish a dedicated communications channel ( circuit) through the network before the nodes may communicate. The circuit guarantees the full ...

communication, for example the

public switched telephone network The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local telep ...

ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Work ...

SONET/SDH Synchronous optical networking (SONET) and synchronous digital hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting dio ...

and optical mesh networks, are intrinsically connection-oriented communications systems. Circuit-mode communication provides guarantees that constant bandwidth will be available and

bit stream A bitstream (or bit stream), also known as binary sequence, is a sequence of bits. A bytestream is a sequence of bytes. Typically, each byte is an 8-bit quantity, and so the term octet stream is sometimes used interchangeably. An octet ma ...

or byte stream data will arrive in order with constant delay. The switches are reconfigured during a circuit establishment phase.

Virtual circuit switching

Packet switched communication may also be connection-oriented, which is called virtual circuit mode communication. Due to the packet switching, the communication may suffer from variable bit rate and delay, due to varying traffic load and packet queue lengths. Connection-oriented communication are not necessarily reliable protocols.

Transport layer

Connection-oriented

transport layer In computer networking, the transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet protocol suite and the OSI model. The protocols of this layer provide end-to-e ...

protocols provide connection-oriented communications over connectionless communications systems. A connection-oriented transport layer protocol, such as TCP, may be based on a connectionless network layer protocol (such as IP), but still achieves in-order delivery of a byte-stream, by means of segment sequence numbering on the sender side, packet buffering and data packet reordering on the receiver side.

Datalink and network layer

In a connection-oriented packet-switched data-link or network-layer protocol, all data is sent over the same path during a communication session. Rather than using complete routing information for each packet (source and destination addresses) as in connectionless datagram switching such as conventional IP routers, a connection-oriented protocol identifies traffic flows only by a channel or data stream number, often denoted virtual circuit identifier (VCI). Routing information may be provided to the network nodes during the connection establishment phase, where the VCI is defined in tables in each node. Thus, the actual packet switching and data transfer can be taken care of by fast hardware, as opposed to slower software-based routing. Typically, this connection identifier is a small integer (for example, 10 bits for Frame Relay and 24 bits for ATM). This makes network switches substantially faster. ATM and Frame Relay, for example, are both examples of connection-oriented, unreliable data link layer protocols. Reliable connectionless protocols exist as well, for example AX.25 network layer protocol when it passes data in I-frames, but this combination is rare, and reliable-connectionless is uncommon in modern networks. Some connection-oriented protocols have been designed or altered to accommodate both connection-oriented and connectionless data.

Examples

Examples of connection-oriented packet-mode communication, i.e. virtual circuit mode communication: *

* Connection-oriented Ethernet * Datagram Congestion Control Protocol * Frame Relay *

General Packet Radio Service General Packet Radio Service (GPRS) is a packet oriented mobile data standard on the 2G and 3G cellular communication network's global system for mobile communications (GSM). GPRS was established by European Telecommunications Standards Ins ...

* IPX/SPX * Multiprotocol Label Switching *

Stream Control Transmission Protocol The Stream Control Transmission Protocol (SCTP) is a computer networking communications protocol in the transport layer of the Internet protocol suite. Originally intended for Signaling System 7 (SS7) message transport in telecommunication, the p ...

Transmission Control Protocol The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonl ...

Transparent Inter-process Communication Transparent Inter Process Communication (TIPC) is an Inter-process communication (IPC) service in Linux designed for cluster-wide operation. It is sometimes presented as ''Cluster Domain Sockets'', in contrast to the well-known ''Unix Domain Socke ...

X.25 X.25 is an ITU-T standard protocol suite for packet-switched data communication in wide area networks (WAN). It was originally defined by the International Telegraph and Telephone Consultative Committee (CCITT, now ITU-T) in a series of drafts a ...

References

{{DEFAULTSORT:Connection-oriented Computer networking Internet architecture Internet protocols Network protocols