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MAC - technical definition

Medium Access Control.The process employed to control the basis on which devices can access a shared medium. In a local area network (LAN), some method of control is required to ensure, or at least improve, the ability of all devices to access the network within a reasonable period of time. It also is important that some method exist to either detect or avoid and to recover from data collisions, caused by multiple transmissions placed on the shared medium simultaneously. Medium access control takes place at Layer 1, the Physical Layer, and Layer 2, the Data Link Layer, of the OSI Reference Model. MAC programmed logic is embedded in a device variously known as a network interface unit (NIU) or network interface card (NIC). Medium access control can be centralized or decentralized. Token Ring LANs centralize that function in a master control station. CATV networks centralize control in a headend. Ethernet LANs decentralize the function, distributing the responsibility among the attached devices. Medium access control also can be either deterministic (e.g.,Token Ring) or non-deterministic (e.g., Ethernet) in nature. See also CATV, Data Link Layer, deterministic, Ethernet, headend, LAN, NIC, NIU, non-deterministic, OSI Reference Model, Physical Layer, and Token Ring.
Move, Add and Change. Activity associated with relocating, activating, disconnecting, or changing the features associated with a station set or some other device or component associated with a voice or data telecommunications system, such as a PBX or LAN router. As vendors generally bill MAC activity typically at a much higher rate than activity associated with the initial installation of a system, plug 'n' play features such as automatic set relocation are highly desirable. See also plug 'n' play and automatic set relocation.

See MAC in Computer

(1) See Macintosh, MAC layer, MAC address, moves-adds-changes and mandatory access control.

(2) (Message Authentication Code) A number computed from the contents of a text message that is used to prove the integrity of a message. The MAC is a checksum that is computed using an algorithm based on the DES or AES ciphers, which use a secret key. The MAC is then sent with the message. The recipient recomputes the MAC at the other end using the same algorithm and secret key and compares it to the one that is sent. If they are the same, it is assumed that the message has not been tampered with.

A MAC is like a digital signature, except that a secret key is used rather than a private key. Also known as the U.S. Government Standard Data Authentication Code (FIPS PUB 113). See digital signature, cryptography and DES.

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