This document summarizes the results of a lab simulation comparing the performance of G.711, G.729, and G.723 codecs. The simulation measured FTP and email download response times, voice traffic received, end-to-end delay, and packet delay variation. Based on the results, the G.729 codec had the best overall performance with minimal impact on data traffic, acceptable delay and jitter ranges, and significantly lower network bandwidth usage compared to G.711. Though G.723 had the lowest bandwidth, its delays were unacceptable. Therefore, the document recommends implementing G.729 for voice traffic.

1. NETW320 Lab for WAN Codec Pg. 1
Lab # 7 Citrix Platform
Greg Pubill
Professor Noel Broman
December 14, 2014
Required Lab Questions for NETW320, Codec Selection for Campus Network (This section is
worth 75% of your grade for this lab.)
1. In the Results browser, expand FTP and select Download Response Time (sec). Change the
view from As Is to time_average and select the Show button. Zoom in on the last two-thirds of
the graph to eliminate start-up oscillation time and to get better granularity of the results. Copy
and label this graph to your lab report. Then use this graph to answer the following questions.
 1. For the G.711 run, estimate the FTP response time.
The G.711 FTP response time was 17.2 seconds
 2. For the G.729 run, estimate the FTP response time.
The G.729 FTP response time was 15.2 seconds
 3. For the G.723.1 run, estimate the FTP response time.
The G.723 FTP response time was 23.7 seconds
FTP Download Response Time Graph
2. Close the FTP tree. Expand E-mail and select Download Response Time (sec). Change the
view from As Is to time_average and select the Show button. Zoom in on the last two-thirds of
the graph to eliminate start-up oscillation time and to get better granularity of the results. Copy
and label this graph to your lab report. Then use this graph to answer the following questions.
 4. For the G.711 run, estimate the E-mail Download response time.

2. NETW320 Lab for WAN Codec Pg. 2
Lab # 7 Citrix Platform
Greg Pubill
Professor Noel Broman
December 14, 2014
The G711 email download response time was: 14.9 seconds
 5. For the G.729 run, estimate the E-mail Download response time.
The G729 email download response time was: 11.3 seconds
 6. For the G.723.1 run, estimate the E-mail Download response time.
The G723 email download response time was: 18.9 seconds
Email Download Response Time Graph

3. NETW320 Lab for WAN Codec Pg. 3
Lab # 7 Citrix Platform
Greg Pubill
Professor Noel Broman
December 14, 2014
3. Close the E-mail tree. Expand Voice and select Traffic Received (bytes/sec). Change the view
from As Is to time_average and select the Show button. Zoom in on the last two-thirds of the
graph to eliminate start-up oscillation time and to get better granularity of the results. Copy and
label this graph to your lab report. Then use this graph to answer the following questions:
 7. For the G.711 run, estimate the Traffic Received in bytes/sec.
The traffic received for G.711 was: 91,388 bytes/sec
 8. For the G.729 run, estimate the Traffic Received in bytes/sec.
The traffic received for G.729 was: 11,425 bytes/sec
 9. For the G.723.1 run, estimate the Traffic Received in bytes/sec.
The traffic received for G.723 was: 7,673 bytes/sec
Bytes Received Graph
4. Go to results and select Compare Results. Expand Voice and select Packet End-to-End Delay
(sec). Change the view from As Is to time_average and select the Show button. Zoom in on the
last two-thirds of the graph to eliminate start-up oscillation time and to get better granularity of the
results. Copy and label this graph to your lab report. Then use this graph to answer the following
questions.
 10. For the G.711 run, estimate the End-to-End Delay for voice packets. Then use this answer
to get the overall delay by taking into account the frame size delay and look ahead delay as
outlined in the introduction. Note: a common mistake is to add millisecond to seconds. Be sure
you convert your data to the same units (i.e., add seconds to seconds or milliseconds to
milliseconds).
Overall delay = End-to-End delay + Frame Size delay + Look Ahead delay
263 + 0.125 + 0 = 263.125 milliseconds = Total G.711 overall end-to-end delay

4. NETW320 Lab for WAN Codec Pg. 4
Lab # 7 Citrix Platform
Greg Pubill
Professor Noel Broman
December 14, 2014
 11. For the G.729 run, estimate the End-to-End Delay for voice packets. The use this answer
to get the overall delay by taking into account the frame size delay and look ahead delay as
outlined in the introduction. Be sure you convert your data to the same units (i.e., add seconds to
seconds or milliseconds to milliseconds).
240 + 10 + 5 = 255 milliseconds = Total G.729 overall end-to-end delay
 12. For the G.723.1 run, estimate the End-to-End Delay for voice packets. Then use this
answer to get the overall delay by taking into account the frame size delay and look ahead delay
as outlined in the introduction. Be sure you convert your data to the same units (i.e., add seconds
to seconds or milliseconds to milliseconds).
373 + 30 + 7.5 = 410.5 milliseconds = Total G.729 overall end-to-end delay
End-to-End Delay Graph
5. Go to results and select Compare Results. Expand Voice and select Packet Delay Variation.
Change the view from As Is to time_average and select the Show button. Zoom in on the last
two-thirds of the graph to eliminate start-up oscillation time and to get better granularity of the
results. Copy and label this graph to your lab report. Then use this graph to answer the following
questions:
 13. For the G.711 run, estimate the Packet Delay Variation for voice packets.
The jitter total was: 0.178 for G.711
 14. For the G.729 run, estimate the Packet Delay Variation for voice packets.
The jitter total was: 0.160 for G.729
 15. For the G.723.1 run, estimate the Packet Delay Variation for voice packets.
The jitter total was: 0.379 for G.723
Voice Packet Delay Variation (Jitter) Graph

5. NETW320 Lab for WAN Codec Pg. 5
Lab # 7 Citrix Platform
Greg Pubill
Professor Noel Broman
December 14, 2014

6. NETW320 Lab for WAN Codec Pg. 6
Lab # 7 Citrix Platform
Greg Pubill
Professor Noel Broman
December 14, 2014
Required Lab Summary Report for NETW320, Codec Selection for Campus Network
Which of the codecs used in this lab would you recommend that the network administrator
implement for the organization under analysis?
The results of this simulation, support the performance values listed and recommended by the
ITU the tables (see tables on last page of report). From these results it can be concluded that
the network shall use the G.729 codec for VoIP communication. This codec will have minimal
email, ftp and http traffic impact, it will also result in acceptable delay and jitter ranges. It will
also result in a significant reduction of network traffic with a total of 11.5 KBps when compared
to 91 KBps generated by G.711. It is true the G.723 carries only 7.6 KBps but the delays fall in
the unacceptable range and it has the lowest MOS value. The G.729 codec should be prefered
as it still maintains an MOS value of 3.92 which is only slightly lower than the 4.1 value of the
G.711 codec.
a. How did particular codec implementations affect FTP download response time and e-
mail download response time? Were any of these delays significant enough to cause
FTP users and e-mail users to become dissatisfied?
Specifically for FTP and email response time the choice of G.729 codec actually improved the
response time. The data collected from the simulation shows that the average response time
was 15.2 for FTP and 11.3 seconds for email using this codec. The next set of results shows
that the second best performing codec was G.711. Email response time for email was 17.2
seconds and FTP response time was 14.9 which can be considered comparable to the G.729
performance. By far the worst perfoming codec was G.723 with the highest response times.
Email and FTP traffic is more tolerant than VoIP traffic. Voice traffic can tolerate response/delay
time of up to 200 ms. Delays higher than this value cause appreciable loss of voice quality, the
delays on data traffic althought they are much higher will still be tolerable in end user
experience.
b. Compare the amount of voice packets generated by the various codecs. What effect
does generating more voice packets for a particular codec have on voice quality?
Why?
Generating more voice packets could have effects that may either be desirable or undesirable
depending on the bandwidth available. Codecs that generate more voice packets will produce
sound of higher quality and less delay due to the fact that less time is spent compressing and
decompressing voice packets. However, when bandwidth is limited this codec can cause
degradation of the conversation as packets will be dropped by the UPD protocol, end users will
need continue to repeat portions of the conversation due to these dropped packets. Data user
will also notice congestion as data traffic will be delayed since TCP will continue to retransmit
until acknowledgements is received.
c. Use the overall delay you calculated for the three codecs used in this lab to rate their
overall delay times with the ITU-T benchmark outlined in the introduction to this lab.

7. NETW320 Lab for WAN Codec Pg. 7
Lab # 7 Citrix Platform
Greg Pubill
Professor Noel Broman
December 14, 2014
Do all codecs fall within recommended parameters? If not, how do you think this
delay will affect the speech quality of the VoIP traffic?
The calculated delays on this simulation show that both the G.711 and G.729 codecs fall within
the acceptable range for One-Way Overall Delay Times recommended by the ITU-T. The G.729
codec had the better performance with a delay of 255 ms, the G.711 codec resulted in a delay
of 263 ms. Since the ITU table shows that an acceptable range exist between 150 to 400 ms.
We can consider these two codecs as suitable. It is always desirable to have delays less than
150 ms in every case, however these results still fall within the range manageable by
administrators. G.723 performance would not be acceptable with a total delay of 410.5 ms.
d. Comment on the effect of your measured packet delay variation for the various
codecs analyzed in this lab. See the comments on packet delay variation (jitter)
outlined in the introduction to this lab. Which codecs are most affected by jitter in the
Internet environment? Do you believe the jitter value for any of the codecs is high
enough to degrade speech quality?
The effects of these codecs on packet-delay variation where very favorable in this simulation.
As the introduction stated a variation of more than 50 ms is considered excessive jitter because
it degrades voice quality. However, from the results we see that even the worst performing
codec which was G.723 produced a variation of only 37 milliseconds. The variation displayed by
the G.711 was 17 ms and G.729 was 16 ms which represents a similar range. All of these
values are well below the 50 ms recommendation. In terms of jitter all of these produced results
satisfactory according to the recommended value.
End