Analysis of Quality of Service in Wimax networks

4.1.4 Comparative Results for all service flows for VOIP traffic
To make the comparison between the different service flows, the data gathered 
from all three service flows is presented on the same chart. This makes it easier to see 
the behavior of different QoS parameters for the same traffic over different type of 
service flow. Figure 18 through Figure 21 show the comparative plots.
Throughput
0
100
200
300
400
500
600
2
4
6
8
10
Number of nodes
kbps
UGS
RTPS
BE
 
Figure 18 Throughput with number of nodes for all service flows 
Service Flow Type: Combined 
Traffic Type: VOIP 
VOIP Codec: G.711 ((64kbps): 80 bytes frame, 160 bytes payload, 50 pkts per sec.) 

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Figure 18 shows the throughput for all three service flows on a single chart. The 
throughput for UGS flow is the highest among the three. The reason for this is that UGS 
flow has the least packet loss. With less number of packets lost, the average throughput 
is higher for UGS. The throughput for rtPS traffic and BE traffic is very similar. UGS 
service flow is designed with constant bit rate traffic in mind. Since a periodic bandwidth 
is allocated by the BS to the MS, the MS is able to send
Packet Loss
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
2
4
6
8
10
Num ber of nodes
%
UGS
RTPS
BE
 
Figure 19 Packet Loss with number of nodes for all service flows 
Figure 19 shows comparative packet loss. UGS service flow has the lowest 
packet loss. This expected behavior. As explained in Chapter 2, UGS is designed to 
support real-time services that generate fixed sized data packets on a periodic basis.
Service Flow Type: Combined
Traffic Type: VOIP 
VOIP Codec: G.711 ((64kbps): 80 bytes frame, 160 bytes payload, 50 pkts per sec.) 

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VOIP applications do exactly that. UGS offers fixed-size grants on a real-time periodic 
basis and does not need the SS to explicitly request bandwidth. The SS is already granted 
a fixed bandwidth and can transmit the data packets in a specific slot during the uplink 
transmission. Bandwidth is not requested regularly as in the case of rtPS service flow. 
Figure 20 shows the average jitter for all the three service flows. The graph is 
drawn on logarithmic scale to make the comparison easy. BE service flow has the 
highest jitter. The average jitter for UGS service flow does not vary as much as the 
number of nodes increases. Secondly the value is very small. UGS service flow is 
designed for VOIP traffic which generates periodic fixed sized packets. Jitter is one of 
the main parameters for indicating the perceived quality of voice as it reaches the 
destination node.