Performance Evaluation of Reservation MAC Protocols
retransmission is not an efficient method for error handling. However, this approach
ensures an observation of the protocol performance without influence of an applied error-
handling method. Application of other ARQ variants that can improve network utilization
are considered in Sec. 6.4.
If the networks with rare transmission requests are analyzed (average packet size of
1500 bytes in the simple data traffic model, Sec. 6.2.3), there is no difference between
ALOHA and the polling reservation MAC protocols (Fig. 6.14). There is a linear increase
in the network utilization from 15% to the maximum values. The maximum network
utilization is reached within the network without disturbances (about 93%). The remaining
7% of the network capacity is allocated for the signaling channel (one of 15 channels).
In the lightly disturbed network, the maximum utilization amounts to 83%, and in the
heavily disturbed network, it is about 50%.
A saturation point can be recognized in the diagram between 300 and 350 stations in
the network without disturbances. Each network station produces on average 2.5 kbps of
offered traffic load (Sec. 6.2.3), which amounts to 750 to 875 kbps for 300 to 350 stations,
according to Eq. 6.1.
average total offered network load
number of network stations
average offered load per station 2.5 kbps
The network has a gross data rate of 896 kbps (14 channels with 64 kbps). However,
according to the size of the data segment payload (28 bytes, Sec. 6.2.4) and Eq. 6.2, it
results in a net capacity of 784 kbps (14 channels with 56 kbps), which also has a total
Number of stations
Average network utilization basic ALOHA and basic polling protocols with rare
transmission requests (average packet size: 1500 bytes)