Multiple Access Protocols in Data Link Layer, Exams of Computer science

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McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000

Multiple Access

Figure 12.1 Data link layer divided into two functionality-oriented sublayers

12-112-1 RANDOM ACCESSRANDOM ACCESS

In In random accessrandom access oror contentioncontention methods, no station ismethods, no station is superior to another station and none is assigned the superior to another station and none is assigned the control over another. No station permits, or does not control over another. No station permits, or does not permit, another station to send. At each instance, a permit, another station to send. At each instance, a station that has data to send uses a procedure defined station that has data to send uses a procedure defined by the protocol to make a decision on whether or not to by the protocol to make a decision on whether or not to send. send. ALOHA Carrier Sense Multiple Access Carrier Sense Multiple Access with Collision Detection Carrier Sense Multiple Access with Collision Avoidance Topics discussed in this section: Topics discussed in this section:

Figure 12.3 Frames in a pure ALOHA network

Figure 12.5 Vulnerable time for pure ALOHA protocol

The throughput for pure ALOHA is

S = G × e

−2G

The maximum throughput

S

max

= 0.184 when G= (1/2).

Note

The throughput for slotted ALOHA is

S = G × e

−G

The maximum throughput

S

max

= 0.368 when G = 1.

Note

Figure 12.7 Vulnerable time for slotted ALOHA protocol

Figure 12.10 Behavior of three persistence methods

Figure 12.11 Flow diagram for three persistence methods

Figure 12.13 Collision and abortion in CSMA/CD

Figure 12.14 Flow diagram for the CSMA/CD

Figure 12.16 Timing in CSMA/CA Interframe space, contention window, ACK

In CSMA/CA, the IFS can also be used to

define the priority of a station or a

frame.

Note