Page 70 - Handout Computer Network.

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3.7.4 Media Access Control

Media Access Control (MAC) refers to protocols that determine which computer on a
shared-medium environment (collision domain) is allowed to transmit the data. MAC, with
LLC, comprises the IEEE version of Layer 2. MAC and LLC are both sublayers of Layer 2.
Two broad categories of MAC exist:

• Deterministic (taking turns)
• Nondeterministic (first come, first served) Token Ring and FDDI are deterministic,
and Ethernet/802.3 is nondeterministic (also called probabilistic).
CSMA/CD is an example of a nondeterministic MAC protocol.

To use this shared-medium technology, Ethernet allows the networking devices to
arbitrate for the right to transmit. Stations on a CSMA/CD network listen for quiet, at which
time it’s okay to transmit. However, if two stations transmit at the same time, a collision occurs
and neither station’s transmission succeeds. All other stations on the network also hear the
collision and wait for silence. The transmitting stations, in turn, each wait a random period of
time (a backoff period) before retransmitting, thus minimizing the probability of a second
collision, as shown in Figure 3-16.

Figure 3-16 shown a CSMA/CD Flowchart Process

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