SEDCF phase 1 vs. AFEDCF

In section 4.3.1, generally speaking, AFEDCF performs best in the view of throughput and satisfaction index, even in the view of fairness index. In section 4.3.3, SEDCF phase 1+2 achieves higher throughput but lower fairness index than SEDCF phase 1 does. Hence, in this section, we are going to exam the performance of SEDCF phase 1 and AFEDCF.

Fig. 4.3-10 shows the throughput of SEDCF phase 1 and AFEDCF. The overall trend of these results is the same as above, which also means the overall throughput is decreasing after there are 15 nodes, while the throughput of phone-type flow increases steady. The difference between the overall throughput of SEDCF phase 1 and AFEDCF is not really large, which means SEDCF phase 1+2 will achieve higher throughput than AFEDCF does. In basic, the throughput performance of SEDCF phase 1 and AFEDCF is similar.

0.7 0.75 0.8 0.85 0.9 0.95 1 1.05

5 10 15 20 25 30 35 40

Number of nodes

Satisfaction index

Phone-SEDCF p1 Video-SEDCF p1 Overall-SEDCF p1 Phone-AFEDCF Video-AFEDCF Overall-AFEDCF

Figure 4.3-11. Satisfaction index of SEDCF phase 1 vs. AFEDCF

Similar as throughput performance, the difference between overall satisfaction indexes of SEDCF phase 1 and AFEDCF is not large. But as we can see in Fig. 4.3-11, the video-type is better protected by SEDCF phase 1, because SEDCF phase 1 take minima required transmission rate to adjust CW, while AFEDCF just provides priority-based QoS support to QoS flows, which may lead lower QoS flows (video-type flows) may sacrifice sooner under the consideration of required transmission rate.

0 0.2 0.4 0.6 0.8 1 1.2

5 10 15 20 25 30 35 40

Number of nodes

Fairness index

Phone-SEDCF p1 Video-SEDCF p1 BE-SEDCF p1 Overall-SEDCF p1 Phone-AFEDCF Video-AFEDCF BE-AFEDCF Overall-AFEDCF

Figure 4.3-12. Fairness index of SEDCF phase 1 vs. AFEDCF

The fairness index of SEDCF phase 1 and AFEDCF is shown in Fig. 4.3-12. The performance of SEDCF phase 1 and AFEDCF are not different until there are more than 15 nodes. The fairness indexes of phone-type flows and best effort flows under two protocols are all over 0.9 no matter how many nodes are there. After there are 15 nodes, both the fairness indexes of video-type flows in SEDCF phase 1 and AFEDCF degrade sharply because the total bandwidth is running out, but fairness index of video-type flows in SEDCF phase 1 reach back to high value sooner (after there are 25 nodes), while the same situation happens in AFEDCF while there are 40 nodes.

This represents SEDCF phase 1 provides better intra class fairness between video-type flows. As to overall fairness index, the performance of SEDCF phase 1 and AFEDCF are almost on a par, the two protocols both provide over certain degree of inter class fairness.

0 500 1000 1500 2000 2500

5 10 15 20 25 30 35 40

Number of nodes

Mean delay (ms)

Phone-AEDCF Video-AEDCF Phone-AFEDCF Video-AFEDCF Phone-SEDCF p1 Video-SEDCF p1 Phone-SEDCF p1+p2 Video-SEDCF p1+p2

Figure 4.3-13. Mean delay of AEDCF vs. AFEDCF vs. SEDCF phase 1 vs.

SEDCF phase 1+2

4.3.5 Mean delay of AEDCF vs. AFEDCF vs. SEDCF phase 1 vs.

SEDCF phase 1+2

Here this section illustrates the comparison of mean end-to-end delay between AEDCF vs. AFEDCF vs. SEDCF phase 1 vs. SEDCF phase 1+2. As satisfaction index, mean delay is also calculated for QoS flows. As we can see in Fig. 4.3-13, the delay of phone-type flow is always bounded in certain area, even in the traffic load is high, which shows that the high priority flows is protected well no matter what protocol is adopted. As to video-type flows, after there are 15 nodes, the delay increase more sharply than that of flow flows because the total available bandwidth is running out, generally speaking, SEDCF performs better than AEDCF and AFEDCF and the difference is getting larger while the number of nodes is increasing, although SEDCF phase1 and SEDCF phase 1+2 are not designed for controlling delay.

Table 4.3-1. Parameter settings of IEEE802.11e MAC layer

4.3.6 SEDCF phase 1 vs. SEDCF phase 1+2 vs. AFEDCF

In order to investigate SEDCF’s performance of QoS guarantee more detail under admission control. This special scenario is upon the same ring topology and assumes at there are just 10 nodes in the ad hoc network to definitely be sure that each QoS flow’s minimum demand can be guaranteed. The MAC parameters used in this scenario are listed in Table 4.3-1. There are still three flow priorities, and all are with the same MAC parameters, constant sending rate and same packet size to eliminate the defect of best effort flows, and the setting here is also compatible to original IEEE 802.11 MAC protocol. The major difference between priorities is the minima required transmission rate. To be satisfied, the QoS demand for high priority and media priority flows are set to be 384 Kbps and 256Kbps, i.e. 75% and 50% successful transmission rate, respectively. Furthermore, the smoothing factor and Tupdate is still 0.8 and 5000 Slot_time, accordingly.

0 200 400 600 800 1000 1200 1400

High priority Medium priority Low priority Overall flow

Thoughput (KB/s)

AFEDCF SEDCF p1 SEDCF p1+2

Figure 4.3-14. Throughput of SEDCF phase 1 vs. SEDCF phase 1+2 vs. AFEDCF

The network throughput and fairness index of SEDCF phase 1 and SEDCF phase 1+2 and AFEDCF are in Figs. 4.3-14 and 4.3-15. We found that the throughputs of these three mechanisms have no much difference in overall throughput, while SEDCF phase 1 and SEDCF phase 1+2 provide QoS guarantee to sacrifice best effort flows.

The reason is that SEDCF no matter phase 1 or phase 1+2 integrates the concept of

“satisfaction degree” and thus an unsatisfied flow has some opportunities to have a smaller CW to contend channel easier, even a fast backoff decreasing procedure.

Besides, due to the same reason, SEDCF no matter phase 1 or phase 1+2 also has better intra-class and inter-class fairness indexes.

0 0.2 0.4 0.6 0.8 1 1.2 1.4

High priority Medium priority Low priority Overall flow

Fairness index

AFEDCF SEDCF p1 SEDCF p1+2

Figure 4.3-15. Fairness index of SEDCF phase 1 vs. SEDCF phase 1+2 vs.

AFEDCF

As to fairness index analysis, SEDCF no matter phase 1 or phase 1+2 perform better than AFEDCF, since at last we consider SD in contention window adjusting procedure, the fair sharing of residual bandwidth is related to the required transmission rate. And AFEDCF do not consider about the required transmission rate, that is the reason the fairness index of AFEDCF is obvious lower than SEDCF phase 1 and SEDCF phase 1+2.

Chapter 5

Conclusion and Future Work

With the growth of wireless network and real-time multimedia application, the importance of Quality of Service (QoS) has been taken more and more seriously.

However, currently the widest used wireless MAC scheme IEEE 802.11 DCF has no QoS support. In this thesis, we discussed the reason DCF cannot offer QoS demand and surveyed some QoS extension to original DCF, including official solution IEEE 802.11e EDCA, and other QoS enhancement based on EDCA, they are AEDCF, AFEDCF and IDFQ, which adapt contention window decision, backoff decreasing mechanism and inter frame space calculation, respectively. Unfortunately, except the service differentiation based on predefined priority, these mechanism provide either higher throughput or partial fairness between the same priority flows or weighted fairness.

Hence, a new media access scheme called Satisfaction Enhanced DCF (SEDCF) is proposed. SEDCF can provide not only priority relationship service differentiation but also satisfaction QoS demand, and global fairness of residual bandwidth, while maintaining high throughput. SEDCF algorithm is separated into two phases, and the performances of SEDCF and other QoS enhancement scheme is also evaluated.

SEDCF phase 1 performs slightly better than SEDCF phase 1+2 in global fairness, while SEDCF phase 1+2 achieves higher total throughput than SEDCF phase 1. As to SEDCF compare to other mechanism, SEDCF achieve higher local and global fairness performance while maintaining or improving throughput.

As to the future work, the global fairness still has space to improve. And SEDCF can work with well designed admission control mechanism, because SEDCF provide

absolute QoS satisfaction based on transmission rate, the network available bandwidth will definitely run out along the number of flows increasing. To operate in coordination with admission control, SEDCF can be applied in situations closer to real world network scenarios, even considering the nodes’ mobility.

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