Performance Evaluation of Reservation MAC Protocols
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0
0.2
0.4
0.6
0.8
1
50 100 150 200 250 300 350 400 450
Throughput
Number of stations
Undisturbed
Lightly
disturbed
Heavily
disturbed
ALOHA & polling
100 150 200 250 300 350 400 450
Number of stations
Polling
ALOHA
Rare requests
Average packet size: 1500 bytes
Frequent requests
Average packet size: 300 bytes
Figure 6.22
Average data throughput per station basic ALOHA and polling protocols
are outlined as network saturation points in heavily and lightly disturbed networks and
the undisturbed network respectively. The behavior of both random and dedicated access
protocols remains the same as well.
The average data throughput in networks with frequent requests also behaves in the
same way. Accordingly, the throughput decreases significantly above 100 network stations
if ALOHA random access protocol is applied to the signaling channel. Dedicated polling
protocol behaves better, but the decrease of the throughput is more significant than in
the network with rare requests, which is also in accordance with the results for network
utilization.
6.3.1.5 Conclusions
The purpose of the investigation of two basic reservation MAC protocols (random and
dedicated access methods realized by slotted ALOHA and polling) is the validation of
the simulation model and its elements, as well as the performance analysis of the basic
protocol solutions. The calculations carried out in parallel (presented above) confirm the
simulation results and prove the accuracy of the simulation model.
Two sets of parameters are used for traffic modeling, to represent networks with rare
and frequent transmission requests (large and small user packets with average sizes of
1500 and 300 bytes respectively). It is shown that network performance depends strongly
on this parameter set, which can be outlined as a suitable solution for the traffic mod-
eling, ensuring protocol investigation and comparison under different traffic conditions.
Noise scenarios applied within the disturbance model decrease the network performances
by approximately 10% in lightly disturbed networks and by 50% in heavily disturbed
networks, which provides a good basis for the observation of disturbance influence on
the protocol and network performance as well.
A strong relationship between network utilization and data throughput is recognized
for both protocol variants and all applied traffic and disturbance models. Access and
transmission delays depend on the signaling delay in low network load area. However, in
the highly loaded networks, they depend strongly on the entire network data rate. On the