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Transport layer
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<h2 id="services">Services</h2> <p>Transport layer services are conveyed to an application via a programming interface to the transport layer protocols. The services may include the following features:<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p> <ul><li><a href="/facts/Connection-oriented_communication/2yAhgueh">Connection-oriented communication</a>:<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> It is normally easier for an application to interpret a connection as a <a href="/facts/Data_stream/57yDhBCd">data stream</a> rather than having to deal with the underlying connection-less models, such as the <a href="/facts/Datagram/TMHVctMz">datagram</a> model of the <a href="/facts/User_Datagram_Protocol/dxLU0D6q">User Datagram Protocol</a> (UDP) and of the <a href="/facts/Internet_Protocol/Qq6VeEal">Internet Protocol</a> (IP).</li> <li>Same order delivery: The network layer doesn't generally guarantee that packets of data will arrive in the same order that they were sent, but often this is a desirable feature. This is usually done through the use of segment numbering, with the receiver passing them to the application in order. This can cause <a href="/facts/Head-of-line_blocking/jJ6X5ufJ">head-of-line blocking</a>.</li> <li><a href="/facts/Reliability_(computer_networking)/v3kGvfvs">Reliability</a>: Packets may be lost during transport due to <a href="/facts/Network_congestion/9ohkRMso">network congestion</a> and errors. By means of an <a href="/facts/Error_detection_code/o2rH8e3n">error detection code</a>, such as a <a href="/facts/Checksum/AqxQ0I8g">checksum</a>, the transport protocol may check that the data is not corrupted, and verify correct receipt by sending an <a href="/facts/Acknowledgement_(data_networks)/NCc7vbwE">ACK</a> or <a href="/facts/NACK/NCc7vbwE">NACK</a> message to the sender. <a href="/facts/Automatic_repeat_request/1bR2urmF">Automatic repeat request</a> schemes may be used to retransmit lost or corrupted data.</li> <li><a href="/facts/Flow_control_(data)/qcdKcLon">Flow control</a>: The rate of data transmission between two nodes must sometimes be managed to prevent a fast sender from transmitting more data than can be supported by the receiving <a href="/facts/Data_buffer/tVy4j2Dc">data buffer</a>, causing a buffer overrun. This can also be used to improve efficiency by reducing <a href="/facts/Buffer_underrun/nbhWvM3h">buffer underrun</a>.</li> <li><a href="/facts/Congestion_avoidance/9ohkRMso">Congestion avoidance</a>: <a href="/facts/Congestion_control/9ohkRMso">Congestion control</a> can control traffic entry into a telecommunications network, so as to avoid <a href="/facts/Congestive_collapse/9ohkRMso">congestive collapse</a> by attempting to avoid oversubscription of any of the processing or <a href="/facts/Data_link/fSNk5Nus">link</a> capabilities of the intermediate nodes and networks and taking resource reducing steps, such as reducing the rate of sending <a href="/facts/Packet_(information_technology)/xCYf8SJu">packets</a>. For example, <a href="/facts/Automatic_repeat_request/1bR2urmF">automatic repeat requests</a> may keep the network in a congested state; this situation can be avoided by adding congestion avoidance to the flow control, including <a href="/facts/TCP_congestion_control/gC9Fer09">slow start</a>. This keeps the bandwidth consumption at a low level in the beginning of the transmission, or after packet retransmission.</li> <li><a href="/facts/Multiplexing/YE7hK8cw">Multiplexing</a>: <a href="/facts/TCP_and_UDP_port/ygoHVKNC">Ports</a> can provide multiple endpoints on a single node. For example, the name on a postal address is a kind of multiplexing and distinguishes between different recipients of the same location. Computer applications will each listen for information on their own ports, which enables the use of more than one <a href="/facts/Network_service/GdLvd2ml">network service</a> at the same time. It is part of the transport layer in the <a href="/facts/TCP/IP_model/KNkxtSpw">TCP/IP model</a>, but of the <a href="/facts/Session_layer/Yxo8uqLr">session layer</a> in the OSI model.</li></ul> <h2 id="analysis">Analysis</h2> <p>The transport layer is responsible for delivering data to the appropriate application process on the host computers. This involves <a href="/facts/Statistical_multiplexing/rLGcaGHV">statistical multiplexing</a> of data from different application processes, i.e. forming data segments, and adding source and destination port numbers in the header of each transport layer data segment. Together with the source and destination IP address, the port numbers constitute a <a href="/facts/Network_socket/r1ldfkb5">network socket</a>, i.e. an identification address of the process-to-process communication. In the OSI model, this function is supported by the <a href="/facts/Session_layer/Yxo8uqLr">session layer</a>. </p><p>Some transport layer protocols, for example TCP, but not UDP, support <a href="/facts/Virtual_circuit/8HqpnTxl">virtual circuits</a>, i.e. provide <a href="/facts/Connection-oriented_communication/2yAhgueh">connection-oriented communication</a> over an underlying packet-oriented <a href="/facts/Datagram/TMHVctMz">datagram</a> network. A byte stream is delivered while hiding the packet mode communication for the application processes. This involves connection establishment, dividing of the data stream into packets called segments, segment numbering and reordering of out-of-order data. </p><p>Finally, some transport layer protocols, for example TCP, but not UDP, provide end-to-end reliable communication, i.e. <a href="/facts/Error_recovery/o2rH8e3n">error recovery</a> by means of <a href="/facts/Error_detecting_code/o2rH8e3n">error detecting code</a> and <a href="/facts/Automatic_repeat_request/1bR2urmF">automatic repeat request</a> (ARQ) protocol. The ARQ protocol also provides <a href="/facts/Flow_control_(data)/qcdKcLon">flow control</a>, which may be combined with <a href="/facts/Congestion_avoidance/9ohkRMso">congestion avoidance</a>. </p><p>UDP is a very simple protocol and does not provide virtual circuits, nor reliable communication, delegating these functions to the <a href="/facts/Application_software/YQuj7Kog">application</a> program. UDP packets are called <a href="/facts/Datagram/TMHVctMz">datagrams</a>, rather than segments. </p><p>TCP is used for many protocols, including <a href="/facts/HTTP/TWtvf7JD">HTTP</a> web browsing and email transfer. UDP may be used for <a href="/facts/Multicast/D9IspSfl">multicasting</a> and <a href="/facts/Broadcasting_(networking)/NRj7gHre">broadcasting</a>, since retransmissions are not possible to a large amount of hosts. UDP typically gives higher <a href="/facts/Throughput/6zAUsXqw">throughput</a> and shorter latency and is therefore often used for real-time multimedia communication where packet loss occasionally can be accepted, for example IP-TV and IP-telephony, and for online computer games. </p><p>Many non-IP-based networks, such as <a href="/facts/X.25/yaGPqw2Y">X.25</a>, <a href="/facts/Frame_Relay/bFdv0qIP">Frame Relay</a> and <a href="/facts/Asynchronous_Transfer_Mode/SzA8ewFL">ATM</a>, implement the connection-oriented communication at the network or data link layer rather than the transport layer. In X.25, in telephone network modems and in wireless communication systems, reliable node-to-node communication is implemented at lower protocol layers. </p><p>The OSI connection-mode transport layer protocol specification defines five classes of transport protocols: <i>TP0</i>, providing the least error recovery, to <i>TP4</i>, which is designed for less reliable networks. </p><p>Due to <a href="/facts/Protocol_ossification/E7nM0WbV">protocol ossification</a>, TCP and UDP are the only widely used transport protocols on the Internet.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> To avoid <a href="/facts/Middlebox/NQTBjrDr">middlebox</a> intolerance, new transport protocols may mimic the <a href="/facts/Wire_image_(networking)/jkWl9TzV">wire image</a> of a tolerated protocol, or <a href="/facts/Encapsulation_(networking)/xttAQnu0">be encapsulated</a> in UDP, accepting some overhead (e.g., due to outer checksums made redundant by inner integrity checks).<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> <a href="/facts/QUIC/nQt0oLRW">QUIC</a> takes the latter approach, rebuilding reliable stream transport on top of UDP.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> </p> <h2 id="protocols">Protocols</h2> <p>This list shows some protocols that are commonly placed in the transport layers of the <a href="/facts/Internet_protocol_suite/KNkxtSpw">Internet protocol suite</a>, the <a href="/facts/OSI_protocols/MEEwuPY1">OSI protocol suite</a>, <a href="/facts/NetWare/cfnyxMzs">NetWare</a>'s <a href="/facts/IPX/SPX/LCEn03Af">IPX/SPX</a>, <a href="/facts/AppleTalk/6j3NRgTl">AppleTalk</a>, and <a href="/facts/Fibre_Channel/C7C0yreb">Fibre Channel</a>. </p> <ul><li>ATP, <a href="/facts/AppleTalk/6j3NRgTl">AppleTalk Transaction Protocol</a></li> <li>CUDP, Cyclic UDP<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a></li> <li>DCCP, <a href="/facts/Datagram_Congestion_Control_Protocol/JyfrtQRn">Datagram Congestion Control Protocol</a></li> <li>FCP, <a href="/facts/Fibre_Channel_Protocol/MzwQK0Ef">Fibre Channel Protocol</a></li> <li>IL, <a href="/facts/IL_Protocol/2Tqatafj">IL Protocol</a></li> <li>MPTCP, <a href="/facts/Multipath_TCP/PrTmCrqp">Multipath TCP</a></li> <li>NORM, NACK-Oriented Reliable Multicast</li> <li><a href="/facts/QUIC/nQt0oLRW">QUIC</a></li> <li>RDP, <a href="/facts/Reliable_Data_Protocol/B5ewkGAN">Reliable Data Protocol</a></li> <li>RUDP, <a href="/facts/Reliable_User_Datagram_Protocol/zL2uXFyW">Reliable User Datagram Protocol</a></li> <li>SCTP, <a href="/facts/Stream_Control_Transmission_Protocol/s8tmzUhz">Stream Control Transmission Protocol</a></li> <li>SPX, <a href="/facts/IPX/SPX/LCEn03Af">Sequenced Packet Exchange</a></li> <li>SST, <a href="/facts/Structured_Stream_Transport/nE85kXgS">Structured Stream Transport</a></li> <li>TCP, <a href="/facts/Transmission_Control_Protocol/WW4sPrt9">Transmission Control Protocol</a></li> <li>UDP, <a href="/facts/User_Datagram_Protocol/dxLU0D6q">User Datagram Protocol</a></li> <li><a href="/facts/UDP-Lite/Bn3YqjzG">UDP-Lite</a></li> <li>μTP, <a href="/facts/Micro_Transport_Protocol/JjDMRI5n">Micro Transport Protocol</a></li></ul> <h3>Comparison of Internet transport layer protocols</h3> <table><tbody><tr><th scope="col">Feature</th><th scope="col"><a href="/facts/User_Datagram_Protocol/dxLU0D6q">UDP</a></th><th scope="col"><a href="/facts/UDP-Lite/Bn3YqjzG">UDP-Lite</a></th><th scope="col"><a href="/facts/Transmission_Control_Protocol/WW4sPrt9">TCP</a></th><th scope="col"><a href="/facts/Multipath_TCP/PrTmCrqp">Multipath TCP</a></th><th scope="col"><a href="/facts/SCTP/s8tmzUhz">SCTP</a></th><th scope="col"><a href="/facts/DCCP/JyfrtQRn">DCCP</a></th><th scope="col"><a href="/facts/RUDP/zL2uXFyW">RUDP</a><a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a></th></tr><tr><td>Packet header size</td><td>8 bytes</td><td>8 bytes</td><td>20–60 bytes</td><td>50–90 bytes</td><td>12 bytes<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a></td><td>12 or 16 bytes</td><td>14+ bytes</td></tr><tr><td>Typical data-packet overhead</td><td>8 bytes</td><td>8 bytes</td><td>20 bytes</td><td>?? bytes</td><td>44–48+ bytes<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a></td><td>12 or 16 bytes</td><td>14 bytes</td></tr><tr><td>Transport-layer packet entity</td><td>Datagram</td><td>Datagram</td><td>Segment</td><td>Segment</td><td>Datagram</td><td>Datagram</td><td>Datagram</td></tr><tr><td>Connection-oriented</td><td>No</td><td>No</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td></tr><tr><td>Reliable transport</td><td>No</td><td>No</td><td>Yes</td><td>Yes</td><td>Yes</td><td>No</td><td>Yes</td></tr><tr><td>Unreliable transport</td><td>Yes</td><td>Yes</td><td>No</td><td>No</td><td>Yes</td><td>Yes</td><td>Yes</td></tr><tr><td>Preserve message boundary</td><td>Yes</td><td>Yes</td><td>No</td><td>No</td><td>Yes</td><td>Yes</td><td>Yes</td></tr><tr><td>Delivery</td><td>Unordered</td><td>Unordered</td><td>Ordered</td><td>Ordered</td><td>Ordered / Unordered</td><td>Unordered</td><td>Unordered</td></tr><tr><td>Data <a href="/facts/Checksum/AqxQ0I8g">checksum</a></td><td>Optional</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Optional</td></tr><tr><td>Checksum size</td><td>16 bits</td><td>16 bits</td><td>16 bits</td><td>16 bits</td><td>32 bits</td><td>16 bits</td><td>16 bits</td></tr><tr><td>Partial <a href="/facts/Checksum/AqxQ0I8g">checksum</a></td><td>No</td><td>Yes</td><td>No</td><td>No</td><td>No</td><td>Yes</td><td>No</td></tr><tr><td>Path <a href="/facts/Maximum_transmission_unit/l2FdKoLa">MTU</a></td><td>No</td><td>No</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>?</td></tr><tr><td><a href="/facts/Flow_control_(data)/qcdKcLon">Flow control</a></td><td>No</td><td>No</td><td>Yes</td><td>Yes</td><td>Yes</td><td>No</td><td>Yes</td></tr><tr><td><a href="/facts/Congestion_control/9ohkRMso">Congestion control</a></td><td>No</td><td>No</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>?</td></tr><tr><td><a href="/facts/Explicit_Congestion_Notification/VKfVXcKp">Explicit Congestion Notification</a></td><td>No</td><td>No</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>?</td></tr><tr><td>Multiple <a href="/facts/Stream_(computing)/2jtBAp0U">streams</a></td><td>No</td><td>No</td><td>No</td><td>No</td><td>Yes</td><td>No</td><td>No</td></tr><tr><td><a href="/facts/Multi-homing/s3FK7EM7">Multi-homing</a></td><td>No</td><td>No</td><td>No</td><td>Yes</td><td>Yes</td><td>No</td><td>No</td></tr><tr><td>Bundling / <a href="/facts/Nagle%27s_algorithm/s0gpGezx">Nagle</a></td><td>No</td><td>No</td><td>Yes</td><td>Yes</td><td>Yes</td><td>No</td><td>?</td></tr></tbody></table> <h3>Comparison of OSI transport protocols</h3> <p>ISO/IEC 8073/ITU-T Recommendation X.224, "Information Technology - Open Systems Interconnection - Protocol for providing the connection-mode transport service", defines five classes of connection-mode transport protocols designated class 0 (TP0) to class 4 (TP4). Class 0 contains no error recovery and was designed for use on network layers that provide error-free connections. Class 4 is closest to TCP, although TCP contains functions, such as the graceful close, which OSI assigns to the session layer. All OSI connection-mode protocol classes provide expedited data and preservation of record boundaries. Detailed characteristics of the classes are shown in the following table:<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> </p> <table><tbody><tr><th scope="col">Service</th><th scope="col">TP0</th><th scope="col">TP1</th><th scope="col">TP2</th><th scope="col">TP3</th><th scope="col">TP4</th></tr><tr><td>Connection-oriented network</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td></tr><tr><td>Connectionless network</td><td>No</td><td>No</td><td>No</td><td>No</td><td>Yes</td></tr><tr><td>Concatenation and separation</td><td>No</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td></tr><tr><td>Segmentation and reassembly</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td><td>Yes</td></tr><tr><td>Error recovery</td><td>No</td><td>Yes</td><td>No</td><td>Yes</td><td>Yes</td></tr><tr><td>Reinitiate connection (if an excessive number of <a href="/facts/Protocol_data_unit/UJMVQEt9">PDUs</a> are unacknowledged)</td><td>No</td><td>Yes</td><td>No</td><td>Yes</td><td>No</td></tr><tr><td>Multiplexing and demultiplexing over a single <a href="/facts/Virtual_circuit/8HqpnTxl">virtual circuit</a></td><td>No</td><td>No</td><td>Yes</td><td>Yes</td><td>Yes</td></tr><tr><td>Explicit flow control</td><td>No</td><td>No</td><td>Yes</td><td>Yes</td><td>Yes</td></tr><tr><td>Retransmission on timeout</td><td>No</td><td>No</td><td>No</td><td>No</td><td>Yes</td></tr><tr><td>Reliable Transport Service</td><td>No</td><td>Yes</td><td>No</td><td>Yes</td><td>Yes</td></tr></tbody></table> <p>There is also a connectionless transport protocol, specified by ISO/IEC 8602/ITU-T Recommendation X.234.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p> <h2 id="bibliography">Bibliography</h2> <ul><li>Corbet, Jonathan (January 29, 2018). <a href="https://lwn.net/Articles/745590/">"QUIC as a solution to protocol ossification"</a>. <i><a href="/facts/LWN.net/8uTsltvM">LWN.net</a></i>.</li> <li>Papastergiou, Giorgos; Fairhurst, Gorry; Ros, David; Brunstrom, Anna; Grinnemo, Karl-Johan; Hurtig, Per; Khademi, Naeem; Tüxen, Michael; Welzl, Michael; Damjanovic, Dragana; Mangiante, Simone (2017). "De-Ossifying the Internet Transport Layer: A Survey and Future Perspectives". <i><a href="/facts/IEEE_Communications_Surveys_%26_Tutorials/ePJz0rHD">IEEE Communications Surveys & Tutorials</a></i>. 19: 619–639. <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1109%2FCOMST.2016.2626780">10.1109/COMST.2016.2626780</a>. <a href="/facts/Hdl_(identifier)/rdebSxmC">hdl</a>:<a href="https://hdl.handle.net/2164%2F8317">2164/8317</a>. <a href="/facts/S2CID_(identifier)/ldJsHa2Y">S2CID</a> <a href="https://api.semanticscholar.org/CorpusID:1846371">1846371</a>.</li></ul> Wikiversity has learning resources about <i> Transport layer</i> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>R. Braden, ed. (October 1989). Requirements for Internet Hosts -- Communication Layers. Network Working Group. doi:10.17487/RFC1122. STD 3. RFC 1122. Internet Standard 3. Updated by RFC 1349, 4379, 5884, 6093, 6298, 6633, 6864, 8029 and 9293. <a href="/wiki/Bob_Braden" target="_blank">/wiki/Bob_Braden</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>R. Braden, ed. (October 1989). Requirements for Internet Hosts -- Communication Layers. Network Working Group. doi:10.17487/RFC1122. STD 3. RFC 1122. Internet Standard 3. Updated by RFC 1349, 4379, 5884, 6093, 6298, 6633, 6864, 8029 and 9293. <a href="/wiki/Bob_Braden" target="_blank">/wiki/Bob_Braden</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"Introducing the Internet Protocol Suite". System Administration Guide, Volume 3. <a href="https://docs.oracle.com/cd/E19455-01/806-0916/6ja85398m/index.html" target="_blank">https://docs.oracle.com/cd/E19455-01/806-0916/6ja85398m/index.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"Transport Layer" (PDF). Galgotias University. <a href="http://103.47.12.35/bitstream/handle/1/4881/659.pdf?sequence=1&isAllowed=y" target="_blank">http://103.47.12.35/bitstream/handle/1/4881/659.pdf?sequence=1&isAllowed=y</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Heena, Khera. "Data Communication and networking" (PDF). Galgotias University. p. 9. <a href="http://103.47.12.35/bitstream/handle/1/4881/659.pdf?sequence=1&isAllowed=y" target="_blank">http://103.47.12.35/bitstream/handle/1/4881/659.pdf?sequence=1&isAllowed=y</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Papastergiou et al. 2017, p. 620-621. - Papastergiou, Giorgos; Fairhurst, Gorry; Ros, David; Brunstrom, Anna; Grinnemo, Karl-Johan; Hurtig, Per; Khademi, Naeem; Tüxen, Michael; Welzl, Michael; Damjanovic, Dragana; Mangiante, Simone (2017). "De-Ossifying the Internet Transport Layer: A Survey and Future Perspectives". IEEE Communications Surveys & Tutorials. 19: 619–639. doi:10.1109/COMST.2016.2626780. hdl:2164/8317. S2CID 1846371. <a href="https://doi.org/10.1109%2FCOMST.2016.2626780" target="_blank">https://doi.org/10.1109%2FCOMST.2016.2626780</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Papastergiou et al. 2017, p. 623-624. - Papastergiou, Giorgos; Fairhurst, Gorry; Ros, David; Brunstrom, Anna; Grinnemo, Karl-Johan; Hurtig, Per; Khademi, Naeem; Tüxen, Michael; Welzl, Michael; Damjanovic, Dragana; Mangiante, Simone (2017). "De-Ossifying the Internet Transport Layer: A Survey and Future Perspectives". IEEE Communications Surveys & Tutorials. 19: 619–639. doi:10.1109/COMST.2016.2626780. hdl:2164/8317. S2CID 1846371. <a href="https://doi.org/10.1109%2FCOMST.2016.2626780" target="_blank">https://doi.org/10.1109%2FCOMST.2016.2626780</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Corbet 2018. - Corbet, Jonathan (January 29, 2018). "QUIC as a solution to protocol ossification". LWN.net. <a href="https://lwn.net/Articles/745590/" target="_blank">https://lwn.net/Articles/745590/</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Brian C. Smith, Cyclic-UDP: A Priority-Driven Best-Effort Protocol (PDF), retrieved February 23, 2020 <a href="https://www.cs.cornell.edu/zeno/Papers/cyclicudp.pdf" target="_blank">https://www.cs.cornell.edu/zeno/Papers/cyclicudp.pdf</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>RUDP is not officially standardized. There have been no standard-related developments since 1999. <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Excluding data chunk headers and overhead chunks. Without embedded chunks, an SCTP packet is essentially useless. <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Counted as follows: 12 bytes SCTP header + 16 bytes DATA chunk header or 20 bytes I-DATA chunk header + 16+ bytes SACK chunk. Additional non-data chunks (e.g. AUTH) and/or headers for additional data chunks, which might easily increase the overhead with 50 bytes or more, not counted. <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>"ITU-T Recommendation X.224 (11/1995) ISO/IEC 8073". Itu.int. Retrieved January 17, 2017. <a href="http://www.itu.int/rec/T-REC-X.224-199511-I/en/" target="_blank">http://www.itu.int/rec/T-REC-X.224-199511-I/en/</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>"ITU-T Recommendation X.234 (07/1994) ISO/IEC 8602". Itu.int. Retrieved January 17, 2017. <a href="http://www.itu.int/rec/T-REC-X.234-199407-I/en/" target="_blank">http://www.itu.int/rec/T-REC-X.234-199407-I/en/</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> </ol>