tailieunhanh - VoIP Technologies Part 14

Tham khảo tài liệu 'voip technologies part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 316 VoIP Technologies a WiMAX Fig. 28. Simulation model b Time s Fig. 29. MOS during movement from WLAN to WiMAX Fig. 30. MOS during movement from WiMAX to WLAN WLAN and no MS is in the WiMAX. Only one MS employs our proposed handover method and it establishes a VoIP call via the WLAN at the start of the simulation. Then the remaining MS which does not employ the proposed method establishes a VoIP call with a CS every five seconds. That is the traffic in the WLAN gradually increases. From Fig. 31 the simulation results show that the MS which employs our proposed method obtains the average uplink MOS of and downlink MOS of . Furthermore we also evaluated the basic performance of our proposed method in a congested WiMAX as depicted in Fig. 28 b . In the simulation scenario 30 MSs are randomly distributed End-to-End Handover Management for VoIP Communications in Ubiquitous Wireless Networks 317 4 3 2 1 0 Uplink MOS .e-- 0 20 40 60 80 100 Time s 4 3 2 1 0 Í1 Downlink MOS .Đ. 0 20 40 60 80 100 Time s y Fig. 31. MOS over congested wireless network WLAN within WiMAX but no MS is in the WLAN. In this study since the acceptable number of VoIP calls in the WiMAX is 20 MSs all VoIP quality is degraded if each MS does not autonomously execute appropriate handover according to the wireless network condition. Here also only one MS employs our proposed method and it establishes a VoIP call through WiMAX at first. After that a new VoIP call is established through WiMAX every three seconds. Figure 32 shows that the MS which employs our proposed method obtains the average uplink MOS of and downlink MOS of . Therefore our proposed method can maintain VoIP communication quality during movement among different types of wireless networks. 4 3 2 1 0 Fig. 32. MOS over congested wireless network WiMAX Donlink MOS .Đ- É- 0 20 40 60 80 100 Time s ạ Ế V ù 6. Conclusion In this chapter we introduced end-to-end .