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What is Media Access Control?

Media Access Control

Media Access Control tends to the job of controlling access to the cable. When a data frame is ready to be transmitted to other station, it is sent one bit at a time.
A signal representing the first bit, for example, a 1 bit, is imposed on the cable the transmission of the 1 bit takes one bit time. The signal for the next bit, for example a 0 bit, is then imposed on the cable and then received and stored by the stations.
This process continues until all bits of the data frame have been sent. A signal could be either a voltage change in the case of twisted pair or co-axial cable or a light pulse on a fiber-optic cable.
A 1 bit must be clearly distinguishable from a 0 bit overlapping signals result in garbled data, so there needs to be a method of sharing the cable to prevent such errors and collisions.
The two most popular methods are carrier Sense Multiple Access with Collision Detection (CSMA/CD)and Token Passing.
Carrier Sense Multiple Access with Collision Detection
Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is a type of access method generally used with bus topologies.
Carrier Sense
Using CSMA/CD, a station listens to the cable to determine whether or not another station is currently transmitting a data frame.
If the medium is quiet, that is, if no other station is sending, the station sends its data.
Multiple access
Multiple access means that when a data frame is transmitted, it is sent to all stations on the network. As the data frame arrives, each receiving station checks the attached destination address.
If the address applies to the station, the station receives and processes the data, otherwise pass it to the next.
Collision Detection
A collision of data results when two stations detect a free cable and begin simultaneously transmitting data.
To reduce the likelihood of another collision, each station generates a random number to determine how ling to wait before retransmitting.
After the appropriate period of time, each station tests the cable to see if it is able to send data or not.
Token passing
With networks that employ a ring topology, the most common media access control method is token passing.
The sending station adds data to the token, along with its address and the address of the recipient.
The token is then passed around the ring so that each station can check the token’s destination address.
The token continuous around the ring until it reaches the address specified by the original sender. When the recipient has copied the information from the token, it returns the token to the originating station to verify that the data was received.
The original sender that passes the token to the next station on the ring, so that the station can send information over the network.