Analysis of QoS Arjuna Mithra Sreenivasan

Objectives Explain the different queuing techniques. Describe factors affecting network voice quality. Analyse the Effects of using different queuing techniques. Evaluating Queuing techniques by measuring QoS parameters.

Topics Why QoS for voice QoS Review Queuing Techniques for VoIP

Network Convergence Run Data,Voice and other application on the same network. -High availability of bandwidth. Reduced Costs. -One infrastructure to maintain. -Aggregated bandwidth (cheaper). -PBX and trunking costs.

Why QoS for voice QoS protects voice over shared media. - the criminal: bursty data application. -loss of 2 packets lowers the quality of voice. QoS can prioritise VoIP -VoIP is sensitive to delay,jitter and packet loss. -Prioritisation minimise those effects.

Operation of QoS

Queuing techniques Priority Queue(PQ)-Strict priority for important traffic. Weighted Fair Queue(WFQ)-It schedules interactive traffic to the front of the queue to reduce delay, and shares the remaining bandwidth between high bandwidth flows. Class based WFQ(CBWFQ)- extends the standard WFQ functionality to provide support for user-defined traffic classes. Low Latency Queue(LLQ)- Combination of PQ and CBWFQ.

Experimental Design Site 1 R1 Internet Site 2 R2 File server (FTP) TRIXBOX IP- PBX S0/ S0/ S0/0 Fa0/ Fa0/ X X

Experimental Methodology Two experiments were conducted -Without QoS -With QoS

Experiment 1 (Without QoS) QoS Parameters is measured. The same experiment is conducted by reducing the bandwidth, to create congestion and QoS parameters are measured. First, calls are initiated, simultaneously the FTP server is accessed.

Analysis of Experiment 1 Results The experiment is conducted with the link speed of 1.5 Mbps. Delay was maintained at 60ms. Jitter and packet loss was negligible. The experiment was conducted with 0.75 Mbps. Resulted in packet loss and jitters.

Experiment 2(With QoS) The experiment was conducted by marking voice packets and implementing queuing techniques. Traffic were identified and grouped into a class and QoS was applied to the traffic classes. PQ,WFQ,CBWFQ and LLQ were the queuing techniques configured. Performance of each queuing technique was observed.

Analysis of Experiment 2 Results. The PQ is configured on each router. Voice packets are on high priority. PQ was configured by creating a priority list and specifying the protocol (udp) and mapping it to the access-list, which specify the udp traffic. The quality of voice was good, but affects FTP application.

Experiment 2(With QoS) WFQ was configured on serial interfaces of both routers. Thresholds were configured default, where high bandwidth conversations were dropped. Jitters obtained did not affect the voice quality, because delay was maintained 70 ms after 8th minute. The packet loss was found of 3% for 3-4 mins. FTP was frozen for few mins.

Experiment 2(With QoS) CBWFQ is configured on both the routers. The is variation in jitters and packet loss which is negligible. LLQ has given good results. Delay was constant and packet loss was negligible.

Conclusion To achieve reliable, high-quality voice over an IP network, which is designed for data communication is an engineering challenge. According to above experiments performed, LLQ has better performed than any other queuing mechanism. Here voice packets are marked using EF for voice which given a very good result with LLQ.