Connection-oriented communication

<h2 id="circuit-switching">Circuit switching</h2>
<p><a href="/facts/Circuit_switched/fJ3vdmAB">Circuit switched</a> communication, for example the <a href="/facts/Public_switched_telephone_network/eVrCTDU7">public switched telephone network</a>, <a href="/facts/ISDN/zcV99rUb">ISDN</a>, <a href="/facts/SONET%2fSDH/G3LgtGS6">SONET/SDH</a> and <a href="/facts/Optical_mesh_network/eJbmso6U">optical mesh networks</a>, are intrinsically connection-oriented communication systems. Circuit-mode communication provides guarantees that constant bandwidth will be available, and <a href="/facts/Bit_stream/Pf9oGYyY">bit stream</a> or <a href="/facts/Byte_stream/Pf9oGYyY">byte stream</a> data will arrive in order with constant delay. The switches are reconfigured during a circuit establishment phase.
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<h2 id="virtual-circuit-switching">Virtual circuit switching</h2>
<p><a href="/facts/Packet_switched/olDlDP1R">Packet switched</a> communication may also be connection-oriented, which is called <a href="/facts/Virtual_circuit/8HqpnTxl">virtual circuit</a> mode communication. Due to packet switching, communication may suffer from variable bit rates and delays, due to varying traffic loads and packet queue lengths. Connection-oriented communication does not necessarily imply <a href="/facts/Reliability_(computer_networking)/v3kGvfvs">reliability</a>.
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<h3>Transport layer</h3>
<p>Connection-oriented <a href="/facts/Transport-layer_protocol/UmIGUCeK">transport-layer protocols</a> provide connection-oriented communications over connectionless communication systems. A connection-oriented transport layer protocol, such as <a href="/facts/Transmission_control_protocol/WW4sPrt9">TCP</a>, may be based on a connectionless <a href="/facts/Network-layer_protocol/L2jAtJzQ">network-layer protocol</a> 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.
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<h3>Datalink and network layer</h3>
<p>In a connection-oriented packet-switched <a href="/facts/Data_link_layer/K9yPufbt">data-link</a> or <a href="/facts/Network-layer_protocol/L2jAtJzQ">network-layer protocol</a>, 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 <a href="/facts/Virtual_circuit_identifier/SzA8ewFL">virtual circuit identifier</a> (VCI). Routing information may be provided to the network nodes during the connection establishment phase, where the VCI is defined in tables within 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.
</p><p>ATM and Frame Relay, for example, are both examples of connection-oriented, <a href="/facts/Reliability_(computer_networking)/v3kGvfvs">unreliable</a> data link layer protocols. Reliable connectionless protocols exist as well, for example <a href="/facts/AX.25/7HlnxQwA">AX.25</a> network layer protocol when it passes data in I-frames, but this combination is rare, and reliable-connectionless is uncommon in modern networks. 
</p><p>Some connection-oriented protocols have been designed or altered to accommodate both connection-oriented and connectionless data.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a>
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<h2 id="examples">Examples</h2>
<p>Examples of connection-oriented packet-mode communication, i.e. virtual circuit mode communication: 
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<ul><li><a href="/facts/Asynchronous_Transfer_Mode/SzA8ewFL">Asynchronous Transfer Mode</a></li>
<li><a href="/facts/Connection-oriented_Ethernet/DuSdx4Vt">Connection-oriented Ethernet</a></li>
<li><a href="/facts/Datagram_Congestion_Control_Protocol/JyfrtQRn">Datagram Congestion Control Protocol</a></li>
<li><a href="/facts/Frame_Relay/bFdv0qIP">Frame Relay</a></li>
<li><a href="/facts/General_Packet_Radio_Service/c4SJD7ov">General Packet Radio Service</a></li>
<li><a href="/facts/IPX%2fSPX/LCEn03Af">IPX/SPX</a></li>
<li><a href="/facts/Multiprotocol_Label_Switching/k7cx1PWw">Multiprotocol Label Switching</a></li>
<li><a href="/facts/Stream_Control_Transmission_Protocol/s8tmzUhz">Stream Control Transmission Protocol</a></li>
<li><a href="/facts/Transmission_Control_Protocol/WW4sPrt9">Transmission Control Protocol</a></li>
<li><a href="/facts/Transparent_Inter-process_Communication/0At90kGo">Transparent Inter-process Communication</a></li>
<li><a href="/facts/X.25/yaGPqw2Y">X.25</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Ramos-Escano; et al. (June 2, 2005). "US Patent Application Publication 2005/0117529 A1". Retrieved May 19, 2008. <a href="https://patents.google.com/patent/US20050117529" target="_blank">https://patents.google.com/patent/US20050117529</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
</ol>

Connection-oriented communication open-in-new

Connection-oriented communication