Editing Medium access control (section)

== Channel access control mechanism ==
The channel access control mechanisms provided by the MAC layer are also known as a [[multiple access method]]. This makes it possible for several stations connected to the same [[Transmission medium|physical medium]] to share it. Examples of shared physical media are [[bus network]]s, [[ring network]]s, hub networks, [[wireless networks]] and [[half-duplex]] point-to-point links. The multiple access method may detect or avoid data packet [[Collision (telecommunications)|collisions]] if a packet mode [[Contention (telecommunications)|contention]] based [[channel access method]] is used, or reserve resources to establish a logical channel if a [[circuit-switched]] or channelization-based channel access method is used. The channel access control mechanism relies on a physical layer [[Multiplexing|multiplex]] scheme.

The most widespread multiple access method is the contention-based [[CSMA/CD]] 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.
 
A multiple access method is not required in a switched [[full-duplex]] network, such as today's switched Ethernet networks, but is often available in the equipment for compatibility reasons.

=== Channel access control mechanism for concurrent transmission ===
Use of directional antennas and [[millimeter-wave]] communication in a [[wireless personal area network]] 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 [[NP-hardness|NP-hard problem]].<ref>{{cite journal|author=Bilal, Muhammad|display-authors=etal|title=Time-Slotted Scheduling Schemes for Multi-hop Concurrent Transmission in WPANs with Directional Antenna|journal=ETRI Journal |volume=36|issue=3|pages=374–384|arxiv=1801.06018|doi=10.4218/etrij.14.0113.0703|year=2014}}</ref>