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Medium access control
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<h2 id="functions-performed-in-the-mac-sublayer">Functions performed in the MAC sublayer</h2> <p>According to IEEE Std 802-2001 section 6.2.3 "MAC sublayer", the primary functions performed by the MAC layer are:<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> </p> <ul><li>Frame delimiting and recognition</li> <li>Addressing of destination stations (both as individual stations and as groups of stations)</li> <li>Conveyance of source-station addressing information</li> <li>Transparent data transfer of LLC PDUs, or of equivalent information in the Ethernet sublayer</li> <li>Protection against errors, generally by means of generating and checking frame check sequences</li> <li>Control of access to the physical transmission medium</li></ul> <p>In the case of <a href="/facts/Ethernet/nMfhU8tU">Ethernet</a>, the functions required of a MAC are:<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> </p> <ul><li>receive/transmit normal frames</li> <li>half-duplex retransmission and backoff functions</li> <li>append/check FCS (<a href="/facts/Frame_check_sequence/ywJNMuHd">frame check sequence</a>)</li> <li>interframe gap enforcement</li> <li>discard malformed frames</li> <li>prepend(tx)/remove(rx) preamble, SFD (<a href="/facts/Start_frame_delimiter/LC4BXFhI">start frame delimiter</a>), and padding</li> <li>half-duplex compatibility: append(tx)/remove(rx) MAC address</li></ul> <h2 id="addressing-mechanism">Addressing mechanism</h2> <p>The local network addresses used in <a href="/facts/IEEE_802/yKy0UEJI">IEEE 802</a> networks and <a href="/facts/FDDI/nowmb0ue">FDDI</a> networks are called <i><a href="/facts/MAC_address/SVcTfgUH">MAC addresses</a></i>; they are based on the addressing scheme that was used in early <a href="/facts/Ethernet/nMfhU8tU">Ethernet</a> implementations. A MAC address is intended as a unique serial number. MAC addresses are typically assigned to network interface hardware at the time of manufacture. The most significant part of the address identifies the manufacturer, who assigns the remainder of the address, thus providing a potentially unique address. This makes it possible for frames to be delivered on a network link that interconnects hosts by some combination of <a href="/facts/Repeater/JTkWvTEP">repeaters</a>, <a href="/facts/Ethernet_hub/t90w5XMX">hubs</a>, <a href="/facts/Network_bridge/5nyTQtNW">bridges</a> and <a href="/facts/Network_switch/CnvmhNYT">switches</a>, but not by <a href="/facts/Network_layer/L2jAtJzQ">network layer</a> <a href="/facts/Router_(computing)/Nh5cIyVf">routers</a>. Thus, for example, when an <a href="/facts/Internet_Protocol/Qq6VeEal">IP</a> packet reaches its destination (sub)network, the destination IP address (a layer 3 or network layer concept) is resolved with the <a href="/facts/Address_Resolution_Protocol/1QyKybkn">Address Resolution Protocol</a> for <a href="/facts/IPv4/bnQ5MEqm">IPv4</a>, or by <a href="/facts/Neighbor_Discovery_Protocol/kEtX2uDb">Neighbor Discovery Protocol</a> (IPv6) into the MAC address (a layer 2 concept) of the destination host. </p><p>Examples of physical networks are <a href="/facts/Ethernet/nMfhU8tU">Ethernet</a> networks and <a href="/facts/Wi-Fi/u94quCsx">Wi-Fi</a> networks, both of which are IEEE 802 networks and use IEEE 802 48-bit MAC addresses. </p><p>A MAC layer is not required in <a href="/facts/Full-duplex/LCULeVxr">full-duplex</a> <a href="/facts/Point-to-point_(telecommunications)/RmGgN1Pj">point-to-point</a> communication, but address fields are included in some point-to-point protocols for compatibility reasons. </p> <h2 id="channel-access-control-mechanism">Channel access control mechanism</h2> <p>The channel access control mechanisms provided by the MAC layer are also known as a <a href="/facts/Multiple_access_method/CdCGxpcu">multiple access method</a>. This makes it possible for several stations connected to the same <a href="/facts/Transmission_medium/yT1uXLmq">physical medium</a> to share it. Examples of shared physical media are <a href="/facts/Bus_network/s29PkQbE">bus networks</a>, <a href="/facts/Ring_network/GDnXYWDv">ring networks</a>, hub networks, <a href="/facts/Wireless_networks/yr4SWTdl">wireless networks</a> and <a href="/facts/Half-duplex/LCULeVxr">half-duplex</a> point-to-point links. The multiple access method may detect or avoid data packet <a href="/facts/Collision_(telecommunications)/GNMdlntV">collisions</a> if a packet mode <a href="/facts/Contention_(telecommunications)/l9lwP4uk">contention</a> based <a href="/facts/Channel_access_method/CdCGxpcu">channel access method</a> is used, or reserve resources to establish a logical channel if a <a href="/facts/Circuit-switched/fJ3vdmAB">circuit-switched</a> or channelization-based channel access method is used. The channel access control mechanism relies on a physical layer <a href="/facts/Multiplexing/YE7hK8cw">multiplex</a> scheme. </p><p>The most widespread multiple access method is the contention-based <a href="/facts/CSMA/CD/N16l6pse">CSMA/CD</a> used in Ethernet networks. This mechanism is only utilized within a network collision domain, for example, an Ethernet bus network or a hub-based star topology network. An Ethernet network may be divided into several collision domains, interconnected by bridges and switches. </p><p>A multiple access method is not required in a switched <a href="/facts/Full-duplex/LCULeVxr">full-duplex</a> network, such as today's switched Ethernet networks, but is often available in the equipment for compatibility reasons. </p> <h3>Channel access control mechanism for concurrent transmission</h3> <p>Use of directional antennas and <a href="/facts/Millimeter-wave/l28Grdmp">millimeter-wave</a> communication in a <a href="/facts/Wireless_personal_area_network/wB0o8m5A">wireless personal area network</a> increases the probability of concurrent scheduling of non‐interfering transmissions in a localized area, which results in an immense increase in network throughput. However, the optimum scheduling of concurrent transmission is an <a href="/facts/NP-hardness/mQeNPv4R">NP-hard problem</a>.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p> <h2 id="cellular-networks">Cellular networks</h2> <p><a href="/facts/Cellular_network/8zA0jQJ9">Cellular networks</a>, such as <a href="/facts/GSM/Sw8QYaLE">GSM</a>, <a href="/facts/UMTS/lhy2RrMw">UMTS</a> or <a href="/facts/LTE_(telecommunication)/72QhwXHT">LTE</a> networks, also use a MAC layer. The MAC protocol in cellular networks is designed to maximize the utilization of the expensive licensed spectrum.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> The <a href="/facts/Air_interface/rXkUSM2p">air interface</a> of a cellular network is at layers 1 and 2 of the OSI model; at layer 2, it is divided into multiple protocol layers. In UMTS and LTE, those protocols are the <a href="/facts/Packet_Data_Convergence_Protocol/1V5hlSus">Packet Data Convergence Protocol</a> (PDCP), the <a href="/facts/Radio_Link_Control/2SXoF6fN">Radio Link Control</a> (RLC) protocol, and the MAC protocol. The base station has absolute control over the air interface and schedules the downlink access as well as the uplink access of all devices. The MAC protocol is specified by <a href="/facts/3GPP/TBrQYKFF">3GPP</a> in TS 25.321<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> for UMTS, TS 36.321<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> for LTE and TS 38.321<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> for <a href="/facts/5G/yVb460m4">5G</a>. </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Isochronous_media_access_controller/MsMf2HVt">Isochronous media access controller</a></li> <li><a href="/facts/Channel_access_method/CdCGxpcu">List of channel access methods</a></li> <li><a href="/facts/MAC-Forced_Forwarding/yoAzlS0T">MAC-Forced Forwarding</a></li> <li><a href="/facts/MACsec/lWXA2H1n">MACsec</a> (IEEE 802.1AE)</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"IEEE 802-2001 (R2007) IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture" (PDF). IEEE. Archived from the original (PDF) on April 29, 2003. <a href="https://web.archive.org/web/20030429223052/http://standards.ieee.org/getieee802/download/802-2001.pdf" target="_blank">https://web.archive.org/web/20030429223052/http://standards.ieee.org/getieee802/download/802-2001.pdf</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>"4.1.4", IEEE 802.3-2002, IEEE, archived from the original on June 16, 2019 <a href="https://standards.ieee.org/ieee/802.3/3259/" target="_blank">https://standards.ieee.org/ieee/802.3/3259/</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Bilal, Muhammad; et al. (2014). "Time-Slotted Scheduling Schemes for Multi-hop Concurrent Transmission in WPANs with Directional Antenna". ETRI Journal. 36 (3): 374–384. arXiv:1801.06018. doi:10.4218/etrij.14.0113.0703. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Guowang Miao; Jens Zander; Ki Won Sung; Ben Slimane (2016). Fundamentals of Mobile Data Networks. Cambridge University Press. ISBN 978-1107143210. <a href="978-1107143210" target="_blank">978-1107143210</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>3GPP TS 25.321 Medium Access Control (MAC) protocol specification <a href="http://www.3gpp.org/ftp/Specs/html-info/25321.htm" target="_blank">http://www.3gpp.org/ftp/Specs/html-info/25321.htm</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>3GPP TS 36.321 Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC) protocol specification <a href="http://www.3gpp.org/ftp/Specs/html-info/36321.htm" target="_blank">http://www.3gpp.org/ftp/Specs/html-info/36321.htm</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>3GPP TS 38.321 NR; Medium Access Control (MAC) protocol specification <a href="http://www.3gpp.org/ftp/Specs/html-info/38321.htm" target="_blank">http://www.3gpp.org/ftp/Specs/html-info/38321.htm</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> </ol>