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)192.168.11.2

TRIXBOX IP-PBX 192.168.0.10

S0/0 192.168.100.1

S0/0192.168.100.2

S0/0

Fa0/1 192.168.10.254

Fa0/1192.168.11.254

192.168.11. X 192.168.10. 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.

• 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.