The standard four class traffic are distributed in the network. Voice over IP (VoIP) is used as the voice traffic, video streaming is used for the video traffic, FTP is used as the background traffic and TFTP is classified as best effort service. 10% of the total traffics is the voice traffic, 20% is the video traffic, 20% is the background traffic, and rest 50% is the best effort traffic.
Figure 7.5 shows the average proportional fairness index for the flows in the network, and Figure 7.6 depicts average Jain fairness index in the network. Proportional fairness index reflects the inter-class service differentiation, while the average Jain fairness index shows the intra-class fairness. Both the figures reveal that the proposed service differentiation and call admission control schemes improve the inter-class service differentiation as well as intra-class fairness in the network.
7.4 Evaluation of the SelG Protocol: Mesh Path Selection
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Average Goodput (Kbps)
Number of Flows SelG HWMP: Proactive HWMP: Reactive HWMP: Hybrid
Figure 7.7: Average Goodput
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Maximum delay experienced (in ms) by a packet Minimum SINR (in dB) faced by a flow
SelG HWMP: Proactive HWMP: Reactive HWMP: Hybrid
Figure 7.8: Average Packet Drop
respect to average goodput for the flows. As mentioned the description of the scenario setup, half of the flows are from routers to the gateway, and rest halves are between two routers. For proactive HWMP protocol, the goodput of the flows between two routers affects as they need to forward the packets via the gateways. Though reactive HWMP
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Average End-to-end Delay (ms)
Number of Flows SelG HWMP: Proactive HWMP: Reactive HWMP: Hybrid
Figure 7.9: Average End-to-end Delay
improves the goodput for these flows, the overall goodput drops because of the excessive control overheads. It has been observed from the experiments, that for some settings the control overhead even goes beyond 20% of the total traffic. The channel variability is more in the indoor environment, which affects the mesh path selection decisions in HWMP. The average variance in the channel quality is measured in terms of signal-to- interference and noise ratio (SINR), and it has been observed, that average SINR variance in our indoor testbed environment is about 40% of the mean SINR value. Further in some cases, the SINR drops to a very low value due to sudden noise from external factors, like signal interference from high voltage electrical devices. It has been observed that, the packets experiences high delay in these cases, for the proactive HWMP protocol. Even the reactive HWMP can not handle these cases, because they rely on the path metric value calculated during the path-establishment phase. From the logs of the individual routers, the maximum delay experienced by a packet of a flow, and the minimum SINR value observed by that flow are calculated2, and a graph is plotted, as shown in Figure 7.8.
The figure reveals, when the channel quality is low, the maximum delay experienced by a
2The minimum SINR value observed by a flow, indicates the minimum SINR value at the routers that may act as a forwarder for that flow. Therefore, for HWMP protocol, the minimum SINR value is observed at one of the routers in the forwarding path. However, for the SelG protocol, the router with the minimum SINR may be one of the candidates from the set of potential forwarders, and not necessarily be the routers in the actual forwarding path.
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Average Jitter (ms)
Number of Flows SelG HWMP: Proactive HWMP: Reactive HWMP: Hybrid
Figure 7.10: Average Jitter
packet is very high in case of the proactive HWMP protocol. Though the reactive HWMP can alleviate a bit, however, the delay is still considerably high. The hybrid mode of HWMP gives an in-between result. This figure indicate that the HWMP protocol can not adapt the link fluctuations. On the contrary, the proposed SelG protocol provides following advantages over the traditional HWMP protocol,
(i) The SelG protocol adapts to the channel fluctuation. Figure 7.8 reveals that for the SelG protocol, even at the low SINR value, the increment in the maximum delay experienced by a packet is low. If one of the candidate from the set of potential forwarders experience sudden SINR drops, SelG may redirect the packet through another router which provides better link value. It may be noted that a low SINR value results in a low link metric value, because of the poor link quality.
(ii) The control overhead for SelG protocol is lower than the HWMP protocol. The lifetime of the entries in SelG forwarding table is more than the lifetime of the entries in the HWMP forwarding table.
Figure 7.9 compares SelG and HWMP with respect to average end-to-end delay.
Because of the reasons analyzed till now, SelG provides lower end-to-end delay than the HWMP protocol. The jitter value is also less for the SelG protocol, as shown in Figure 7.10.
Because of the route stability and minimum interference interface selection, the proposed
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Fairness index
Number of Flows SelG HWMP: Proactive HWMP: Reactive HWMP: Hybrid
Figure 7.11: Fairness Index
SelG protocol provides better fairness among the flows, compared to the HWMP protocol, as reflected in Figure 7.11. The graph shows that proactive HWMP provides more fairness compared to the reactive HWMP. The reason is that all the flows are forwarded through the mesh gates, and therefore, the maximum goodput for all the flows is bounded to the network capacity of the mesh gates. Reactive HWMP distributes flows unevenly in network, and may result in network congestion, as discussed earlier, which is reflected in fairness calculation. The adaptive next-hop selection based on interference constraint, as used in the proposed SelG protocol, improves the network performance significantly.