Transcript PPT - Napier

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
Site 2 R2
S0/0
192.168.100.
1
S0/0
192.168.100.2
Internet
S0/0
Fa0/1
192.168.11.254
Fa0/1
192.168.10.254
File server
(FTP)
192.168.11.2
TRIXBOX IPPBX
192.168.0.10
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.