A sample text widget

Etiam pulvinar consectetur dolor sed malesuada. Ut convallis euismod dolor nec pretium. Nunc ut tristique massa.

Nam sodales mi vitae dolor ullamcorper et vulputate enim accumsan. Morbi orci magna, tincidunt vitae molestie nec, molestie at mi. Nulla nulla lorem, suscipit in posuere in, interdum non magna.

What is Media Access Control? What is the reason for MAC?

About Media Access Control or MAC

– Media access control or MAC is a data communication protocol that is used in the 7 layer OSI computer networking model.
– This is implemented in the data link layer’s (which is layer 2 itself) sub – layer.
– The purpose of this MAC sub layer is to provide channel access control and addressing mechanisms.
– These mechanisms are important for various network nodes and terminals that use them for establishing communication in a shared medium that lies within a multiple access network such as Ethernet.
– The hardware used for the implementation of the MAC is called the medium access controller.
– The MAC sub – layer resides at the interface intermediate to that of the physical layer of the network and the LLC i.e., the logical link control.
– In a multi – point network this layer is responsible for the emulation of the full – duplex logical communication channel.

Functions of MAC Sub-Layer

The following functions are carried out in the MAC sub – layer:
– Receiving and transmitting the normal frames.
– Back off and half – duplex transmitting functions.
– Checking and appending frame check sequence or FCS.
– Inter – frame gap enforcement
– Discarding the frames that are not formed properly.
– Removing and appending SFD, padding and preamble.
– Appending and removing the MAC address i.e., the half – duplex compatibility

Addressing Mechanism in the MAC Sub–Layer

– Mac address is the local network address that is particularly used in IP – Ethernet.
– MAC address is nothing but another name for this addressing mechanism.
– It is actually a unique serial number.
– This number is assigned to every network interface at the time of manufacturing so that it becomes uniquely identifiable among all the devices in the world.
– All the devices in a network thus have unique identities.
– This is required for making possible the delivery of the data packets to the exact destination host in the network.
– When the data packet reaches the destination, its IP address is resolved by either of the two in to the destination’s MAC address:
1. By address resolution protocol (IPv4)
2. Neighbor discovery protocol (IPv6)

– Ethernet provides the best example for a physical network that is extendable by WLAN access points and network adapters.
– This is so because both have the same hierarchy of 48 – bit MAC address.
– However, in a full–duplex point–to–point communication there is no use for MAC layer but it does require some address fields for maintaining compatibility in point – to – point protocols.
– Channel access control mechanism, also referred to as the multiple access protocol can connect several stations that are connected with the same medium can share it.
– Some examples of such shared media are:
1. Ring networks
2. Bus networks
3. Wireless networks
4. Hub networks
5. Half – duplex point – to – point links

– This whole mechanism is dependent up on a multiplex scheme for physical layer.
– The most widely used protocol in this category is CSMA/ CD based up on contention.
– However, this mechanism is supposed to operate only in a network collision domain and is not of any use in the full-duplex networks.
– But still it is supplied along with the equipment for the reasons of compatibility.
– Some other such protocols are:
1. Token passing
2. Token bus
3. Token ring
4. Dynamic TDMA

Thus, the two major functions of the MAC can be summarized as shown:
1. Data encapsulation i.e., transmitting and receiving. It further includes:
– Framing operations such as frame synchronization and boundary delimitation.
– Addressing operations like handling various addresses.
– Error detection including physical medium transmission errors.

2. Media access management: It consists of two sub – functions:
– Medium allocation i.e., collision avoidance
– Contention resolution or the collision handling
There is one optional MAC control sub layer that might be placed between the MAC and the LLC.

Leave a Reply

You can use these HTML tags

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>