CHAPTER 4 M-TAIWAN EXPERIENCE IN VOIP-WIMAX TRIAL
4.6.3 One‐way Packet Delay
In Figure 4.11 (a), the average one-way packet delay (including 10 IP hops and two WiMAX radio links) is less than 45 ms for stationary CPEs, and is less than 52 ms for moving CPEs.
The delay increases as the CPE speed increases (because of the handover impact).
When the background traffic increases, the one-way packet delay tends to increase for moving
CPEs. The background traffic effect on stationary CPEs is negligible.
(a) Average One-way Packet Delay (ms)
(b) CPE Speed: 0 Km/h (Uplink Background Traffic: 3 Mbps)
(c) CPE Speed: 30 Km/h (Uplink Background Traffic: 3 Mbps)
(d) CPE Speed: 50 Km/h (Uplink Background Traffic: 3 Mbps) Figure 4.11 One-way Packet Delay Measurements
Figures 4.11 (b)-(d) illustrate an example of real-time packet delay measurements with different CPE speeds. When both CPEs are stationary, packet delays are always less than 63 ms. The 5-minute average packet delay is 44 ms at CPE1, and 40 ms at CPE2.
At the speed of 30 Km/h (Figure 4.11 (c)), most packet delays are less than 88 ms, and the maximum packet delay is 132 ms occurring at the handover. The 2-minute average packet delay is 51 ms (for CPE1) and 50 ms (for CPE2). At the speed of 50 Km/h (Figure 4.11 (d)), most packet delays are less than 100 ms, and the maximum packet delay is 289 ms. The 2-minute average packet delay is 55 ms (for CPE1) and 49 ms (for CPE2).
In our experiments, most packet delays are much less than the acceptable upper limit of packet delay (i.e., 150 ms).
4.6.4 Jitters
Figure 4.12 (a) shows that the average jitter is less than 4.3 ms for stationary CPEs, and is less than 6 ms for moving CPEs. Our experiments indicate that for stationary CPEs, the background traffic seems not affect jitter. For moving CPEs, jitter increases as the background
traffic increases. However, it is not clear why CPE speed at 30 Km/h tends to have the worst jitter performance (such phenomenon was also observed in other experiments).
(a) Average Jitter (ms)
(b) CPE Speed: 0 Km/h (Uplink Background Traffic: 3 Mbps)
Uplink
(d) CPE Speed: 50 Km/h (Uplink Background Traffic: 3 Mbps) Figure 4.12 Jitter Measurements
Figures 4.12 (b)-(d) give examples of real-time jitters measurements. When both CPEs are stationary, all jitters values are less than 27 ms. The 5-minute average jitter is 2.23 ms at CPE1, and 2.42 ms at CPE2.
At the speed of 30 Km/h (Figure 4.12 (c)), the maximum jitter is 34 ms when the handover occurs. The 2-minute average jitter values are 5.225 ms (for CPE1) and 6.6 ms (for CPE2). At the speed of 50 Km/h (Figure 4.12 (d)), maximum jitter is 27 ms. The average jitters values are 4.2 ms (for CPE1) and 5.75 ms (for CPE2). After the handover, jitters occur in bursts.
Figure 12 (c) and (d) show that jitter is more seriously affected by handover at 30 Km/h than that at 50 Km/h.
The study also indicates the following observations:
z The impact of background traffic on VoIP is mostly insignificant.
z The MOS values are slightly decreases as the CPE speed increases. The MOS values are not affected by the background traffic.
z The packet loss increases as the CPE speed increases. The packet loss of stationary CPE is insignificant, and is not affected by the background traffic. On the other hand, the background traffic significantly affects the moving CPEs.
z The one-way packet delay increases as the CPE speed increases. The background traffic slightly affects the packet delays for moving CPEs. The background traffic effect on stationary CPEs is negligible.
z Impacts of CPE speed and background traffic on the jitters is not clear in our study.
However, all experiments indicate resilience against jitters.
z The values of all jitter-samples observed in our study are much lower than the unacceptable jitter value (i.e., 25 ms).
4.7 Conclusions
Our investigation upon the experimental results indicates the performance of a VoIP service using the WiMAX-based infrastructure of the M-Taiwan Program conforms very well to the standard requirements of G.107 under the worse-condition and stringent scenario where both VoIP CPEs are wirelessly connected to the same WiMAX base station with both moving CPEs at the speeds up to 50 Km/h while both going under handovers at the same time.
Chapter 5
Conclusions and Future Work
Voice over Internet Protocol (VoIP) is a promising low-cost voice communication over the wired or wireless Internet network. In the mobile/wireless environment, the radio resource is restricted and the reliability of the wireless transmission is much poor than that of the wired environment. To provide satisfactory VoIP services in the mobile/wireless network, the Quality of Service (QoS) of the mobile/wireless network should be guaranteed. This dissertation investigated the VoIP performance in the mobile/wireless network environment.
This chapter concludes our work presented in this dissertation, and briefly discusses future directions of our work.
5.1 Concluding Remarks
In Chapter 2, we conducted a modeling study to tune the IEEE 802.1X parameters to yield better performance. In the IEEE 802.1X standard, several timeout timers are defined for message exchanges in the authentication mechanism, where the same fixed value is suggested for these timeout timers. We observed that the delays for the Extensible Authentication Protocol over LAN (EAPOL) message exchanges may significantly vary. In this WLAN-3G integrated security approach, the access of Home Location Register/Authentication Center (HLR/AuC) in the 3G network may incur long delay. Therefore the setup of timeout periods is very critical for WLAN VoIP call setup. To decrease the false failure detection probability and significantly improve the expected response time of the IEEE 802.1X authentication procedure, we provided guidelines to select appropriate timeout values for IEEE 802.1X operation.
In Chapter 3, we provided guidelines to select appropriate system parameter values for VoIP in the environment (i.e., WLAN network). In 3GPP specifications, the authenticated WLAN Mobile Station (MS) is allowed to access the 3G network through a WLAN Access Gateway/Packet Data Gateway (WAG/PDG). However, to ensure telecom grade security, the VoIP traffic between the MS and the WAG/PDG must be protected with IPsec. We analyzed the performance of IPsec-based VoIP service in a IEEE 802.11b WLAN environment.
Specifically, an IEEE 802.11b AP can support 15 IPsec VoIP connections with acceptable latency, small jitter, and no packet loss. We also indicated that the IPsec overhead is not serious. To maintain the same packet loss rate and jitter, the system will support one less IPsec VoIP connection than original VoIP connection.
In Chapter 4, we investigated the VoIP performance in the vehicle environment. We conducted trials in the real Worldwide Interoperability for Microwave Access (WiMAX) network which supports high-speed mobile broadband services and investigated the WiMAX-based VoIP of a Mobile Taiwan (M-Taiwan) funded program conducted during 2007-08 in the Taipei area. We observed that the performance of a VoIP service using the WiMAX-based infrastructure of the M-Taiwan Program conforms very well to the standard requirements of G.107 under the worse-condition and stringent scenario where both VoIP CPEs are wirelessly connected to the same WiMAX base station with both moving CPEs at the speeds up to 50 Km/h while both going under handovers at the same time.
5.2 Future Work
Based on the research results of this dissertation, the following issues can be further investigated:
Videophone Service: In this dissertation, we evaluated the VoIP performance according to the packet loss, latency, and jitter of the voice streams. Base on the previous IP voice studies, we will further analyze the video performance in the IP Multimedia Core Network Subsystem (IMS) network. ITU-T Recommendation G.1070 proposed an algorithm to estimate the videophone quality [29]. However, the proposed computation model estimates the speech quality and video quality individually, which is not practical in videophone performance measurement. We will further study the video quality affected by speech quality and vice versa to estimate the performance of the videophone service.
Call Transmission Performance: In this dissertation, we focused on the VoIP services involving the endpoints in the same wireless environment. In the further study, we will study the call transmission performance that the endpoints are located in different wireless access networks; for example, one is in the WLAN and the other is in the WiMAX network. Furthermore, we are interested in the next generation 3GPP radio access network called Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) [30] and we will evaluate the call transmission performance of the VoIP services involving the endpoints in the next generation mobile network and the current wireless network.
Internet Call Server: In this dissertation, we discussed the telecom-grade call control and the security performance of the mobile wireless network. In the further study, we will investigate the service performance in a managed IP network, where the call application server is developed on the IBM WsT platform described in Chapter 1 and the mobile user connects to the Chunghwa Telecom (CHT) IMS network. We will show a telecom-grade call server implementation example using the IBM WsT
platform and evaluate the performance of the Internet call services. This study will provide a guideline for the third party service provider.
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Curriculum Vitae
Ya-Chin Sung received the B.S. and the M.S. degrees from National Chiao