Media Access Control


Media Access Control

The Media Access Control (MAC) data communication protocol sub-layer, also known as the Medium Access Control, is a sublayer of the Data Link Layer specified in the seven-layer OSI model (layer 2). It provides addressing and channel access control mechanisms that make it possible for several terminals or network nodes to communicate within a multipoint network, typically a local area network (LAN) or metropolitan area network (MAN).

The MAC sub-layer acts as an interface between the Logical Link Control (LLC) sublayer and the network's physical layer.The MAC layer emulates a full-duplex logical communication channel in a multipoint network. This channel may provide unicast, multicast or broadcast communication service.

Addressing mechanism

The MAC layer addressing mechanism is called physical address or MAC address. This is a unique serial number assigned to each network adapter, making it possible to deliver data packets to a destination within a subnetwork, i.e. a physical network consisting of one or several network segments interconnected by repeaters, hubs, bridges and switches, but not by IP routers. An IP router may interconnect several subnets.

An example of a physical network is an Ethernet network, perhaps extended by Wireless Local Area Networks (WLAN) accesspoints and WLAN network adapters, since these share the same 48-bit MAC address hierarchy as Ethernet.

A MAC layer is not required in full-duplex point-to-point communication, but address fields are included in some point-to-point protocols for compatibility reasons.

Channel access control mechanism

The channel access control mechanisms provided by the MAC layer are also known as a multiple access protocol. This makes it possible for several stations connected to the same physical medium to share it. Examples of shared physical media are bus networks, ring networks, hub networks, wireless networks and half-duplex point-to-point links. The multiple access protocol may detect or avoid data packet collisions if a packet mode 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 multiplex scheme.

The most widespread multiple access protocol is the contention based CSMA/CD protocol used in Ethernet networks. This mechanism is only utilized within a network collision domain, for example an Ethernet bus network or a hub network. An Ethernet network may be divided into several collision domains, interconnected by bridges and switches. A multiple access protocol 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.

Common multiple access protocols

Examples of common packet mode multiple access protocols for wired multi-drop networks are:
* CSMA/CD (used in Ethernet and IEEE 802.3)
* Token bus (IEEE 802.4)
* Token ring (IEEE 802.5)
* Token passing (used in FDDI)

Examples of common multiple access protocols that may be used in packet radio wireless networks are:
* CSMA/CA (used in IEEE 802.11/WiFi WLANs)
* Slotted ALOHA
* Dynamic TDMA
* Reservation ALOHA (R-ALOHA)
* CDMA
* OFDMA

For a more extensive list, see List of channel access methods.

ee also

*Channel access method
*MAC address
*Ethernet and CSMA/CD
*Token Ring and token passing
* CSMA/CA
*MAC-Forced Forwarding
*MLME
*SoftMAC


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Media Access Control — (MAC), уровень управления доступом к среде (передачи) подуровень протокола передачи данных, также известен, как Medium Access Control. Является подуровнем канального (второго) уровня модели OSI. MAC обеспечивает адресацию и механизмы управления… …   Википедия

  • Media Access Control —   [Abk. MAC, dt. »Medienzugriffssteuerung«], Kommunikationsprotokoll für lokale Netzwerke nach einem der 802.x Standards. Man betrachtet die MAC als eine Unterschicht der Sicherungsschicht (OSI Schichtenmodell), die den Kanalzugriff und die… …   Universal-Lexikon

  • Media access control — The OSI model 7 Application layer 6 Presentation layer 5 Session layer 4 Transport layer 3 Network layer 2 …   Wikipedia

  • Media Access Control — Schicht ursprünglich erweitert 7 Anwendung Anwendung 6 Darstellung Darstellung 5 Sitzung Sitzung 4 Transport Transport 3 …   Deutsch Wikipedia

  • Media Access Control — Contrôle d accès au support Pile de protocoles 7 • Application 6 • Présentation 5 • Session 4 • …   Wikipédia en Français

  • Media access control — Contrôle d accès au support Pile de protocoles 7 • Application 6 • Présentation 5 • Session 4 • …   Wikipédia en Français

  • media access control —    Abbreviated MAC. The lower component of the datalink layer that governs access to the transmission medium. The logical link control layer is the upper component of the datalink layer. MAC is used in CSMA/CD and token ring LANs as well as in… …   Dictionary of networking

  • MEDIA ACCESS CONTROL — (MAC) управление доступом к средепротокол, используемый для определения способа получения доступа рабочих станций к среде передачи, наиболее часто используемый в локальных сетях. Для ЛВС, соответствующих стандартам IEEE, MAC уровень является… …   Словарь электронного бизнеса

  • media access control protocol —    See access control list …   Dictionary of networking

  • media access control sublayer —    See MAC sublayer …   IT glossary of terms, acronyms and abbreviations


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.