Media Access Control Method:
A media access control function is to control the
network data transfer between the two computer terminals. It lies in the data link
layer of the OSI Model. The data link layer of the OSI Model consists of the MAC sublayer
and logical link control (LLC) sublayer. The MAC provides flow control and
multiplexing for the transmission medium whereas LLC provides flow control and
multiplexing for the logical link. MAC
layer ensures the collision between the data packets and whenever there is a
collision, it ensures that the sender and receiver get an acknowledgment about it.
There are four ways by which we can achieve collision-free data transmission. These are as below:
1.
Carrier
Sense Multiple Access with Collision Avoidance (CSMA/CA)
In this method, each computer takes an acknowledgment
before transmission. Collision avoidance means that when a sender transmits and
if it detects a collision, then it will wait for some time and then re-transmit
the data packet. However, this process is slow and add additional cost to the
sender.
2.
Carrier
Sense Multiple Access with Collision Detection (CSMA/CD)
In this method, when a collision is detected by media
access control, then the sender will wait for a random amount of time before transmitting
starts again. It is faster than and but not as efficient as CSMA/CA in
preventing network collisions. Both CSMA/CA
and CSMA/CD is used in the Ethernet network.
3.
Demand
Priority
It is the improved version of CSMA/CD. It uses the
concept of active hub and each sender or terminal has to obtain authorization
from the active hub before the transmitting data.
4.
Token Passing
To prevent the collision, the concept of the token is used.
Only the computers that possess a token, are authorized to transmit first. Within
the computer having token, transmission occurs according to the order of higher
to lower priority.
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