1. Test Methodology for Measuring Loss, Delay and Jitter
September 2004
doc.: IEEE /1009
Jan 2006
Test Methodology for Measuring Loss, Delay and Jitter
Date:
Authors:
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Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

2. September 2004
doc.: IEEE /1009
Jan 2006
Abstract
This presentation is the companion presentation for document 11-06/0004r0, which contains text for inclusion into the TGT draft. In these documents, test methodologies for measuring the packet loss, packet latency and packet jitter are proposed.
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

3. Jan 2006
Purpose of the Tests
Packet Loss, Packet Latency and Packet Jitter are all secondary metrics that are key in characterizing the behavior of latency-sensitive usage cases such as VOIP, video conferencing and Internet gaming.
Characterization of Packet Loss, Packet Latency and Packet Jitter in a DUT or a system provides important information to system designers and planners
“What is the probability of a codec jitter buffer under run?”
“Is the packet delay adequate for my application to run?”
Results presented in form of cumulative distribution function (CDF) enable these questions to be answered directly
Chris Trecker, Azimuth Systems

4. September 2004
doc.: IEEE /1009
Jan 2006
Packet Loss
Packet Loss is a secondary metric that measures packets lost in transmission over a data network between two network endpoints.
The Packet Loss Metric is defined as a percentage: The number of packets lost divided by the number of packets expected.
Packet Transmission:
Packet 1
Packet Reception:
Packet 2
Packet 3
Packet 4
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

5. September 2004
doc.: IEEE /1009
Jan 2006
Packet Delay
Latency is a secondary metric that measures the latency between the transmission and the reception of a data packet between two network endpoints.
Latency is measured in seconds.
Receiver
Transmitter
Data Network
Packet Latency
packet is
transmitted
packet is
received
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

6. September 2004
doc.: IEEE /1009
Jan 2006
Packet Jitter
Jitter is a secondary metric. Jitter is an estimate of the statistical variance of data packet interarrival time. This will be calculated using the formula presented in section of RFC 1889 for interarrival jitter.
10 ms
10 ms
10 ms
Packet Transmission:
Packet 1
Packet 2
Packet 3
Packet 4
11 ms
9 ms
11 ms
Packet Reception:
Packet 1
Packet 2
Packet 3
Packet 4
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

7. Packet Jitter Calculation
September 2004
doc.: IEEE /1009
Jan 2006
Packet Jitter Calculation
The interarrival jitter J is defined to be the mean deviation (smoothed absolute value) of the difference D in packet spacing at the receiver compared to the sender for a pair of packets (RFC 1889). The formula presented in section of RFC 1889 for interarrival jitter is used..
Example using the illustration on Slide 6:
D(1,2) = (T2 – T1) – (A2 – A1) Where D(1,2) is the difference between packets 1 and 2. T2 and T1 are the transmit times of packets 1 and 2. A2 and A1 are the arrival times of packets 1 and 2.
Jitter is recalculated every time D is calculated. In this example, the jitter calculation starts after packet 2 is received.
J = J + ( | D | ) / 16
After packet two is received, D can be calculated as follows: 10 – 11 = -1. The initial value for J is zero, so J = 1 / 16.
After packet three is received, D can be calculated as 10 – 9 = 1. The new D value is then plugged into the jitter function as follows: J = 1/16 + (1/16) = 1/8.
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

8. System Test Configuration
September 2004
doc.: IEEE /1009
Jan 2006
System Test Configuration
Background and
Latency-Sensitive
Traffic
Shielded Enclosure
Application Specific Server (i.e., VOIP server) if applicable
Latency-Sensitive
Traffic
DS Traffic Generator (optional)
STA UT (i.e., VOIP phone)
Shielded Enclosure
Background and
Latency-Sensitive
Traffic
Latency-Sensitive
Traffic
AP UT
SETE (optional)
Application Node (i.e., VOIP phone)
and DS Traffic Analyzer
Legend:
RF cables
Wired LAN cables
Variable
Attenuator
SETE – Station Emulation Test Equipment
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

9. System Test Configuration
September 2004
doc.: IEEE /1009
Jan 2006
System Test Configuration
The System Test Configuration is ideal for testing off-the-shelf components in a system configuration.
The STA Emulation Test Equipment (SETE) is useful for introducing additional capacity and traffic types into the system test.
The and DS traffic analyzers must have synchronized time-stamps in order to properly calculate packet latency.
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

10. STA Test Configuration
September 2004
doc.: IEEE /1009
Jan 2006
STA Test Configuration
Latency-Sensitive Traffic
Shielded Enclosure
AETE or off-the-shelf AP
STA UT
Traffic Analyzer
RF Cables
Variable
Attenuator
Legend:
AETE – AP Emulation Test Equipment
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

11. STA Test Configuration
September 2004
doc.: IEEE /1009
Jan 2006
STA Test Configuration
The STA Test Configuration is ideal for testing STA in a controlled environment with a limited number of variables.
The AP Emulation Test Equipment (AETE) or off-the-shelf AP can be used.
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

12. AP Test Configuration September 2004 doc.: IEEE 802.11-04/1009
Jan 2006
AP Test Configuration
Background and Latency-Sensitive Traffic
Latency-Sensitive
Traffic
SETE - 1
DS Traffic Generator
Shielded Enclosure
Background
Traffic
AP UT
SETE - 2
and DS Traffic Analyzer
RF cables
Variable
Attenuator
Legend:
Wired LAN cables
SETE – Station Emulation Test Equipment
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

13. September 2004
doc.: IEEE /1009
Jan 2006
AP Test Configuration
The AP Test Configuration is ideal for AP capacity as it relates to packet loss, latency and jitter.
The STA Emulation Test Equipment (SETE) is useful for introducing additional capacity and traffic types into the AP Test.
The and DS traffic analyzers must have synchronized time-stamps in order to properly calculate packet latency.
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

14. Packet Loss Results from VOIP Test
September 2004
doc.: IEEE /1009
Jan 2006
Packet Loss Results from VOIP Test
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

15. Packet Loss Results from VOIP Test
September 2004
doc.: IEEE /1009
Jan 2006
Packet Loss Results from VOIP Test
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

16. Packet Delay Results from VOIP Test
September 2004
doc.: IEEE /1009
Jan 2006
Packet Delay Results from VOIP Test
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

17. Packet Delay Results from VOIP Test
September 2004
doc.: IEEE /1009
Jan 2006
Packet Delay Results from VOIP Test
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

18. Packet Jitter Results from VOIP Test
September 2004
doc.: IEEE /1009
Jan 2006
Packet Jitter Results from VOIP Test
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

19. Packet Jitter Results from VOIP Test
September 2004
doc.: IEEE /1009
Jan 2006
Packet Jitter Results from VOIP Test
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al

20. September 2004
doc.: IEEE /1009
Jan 2006
Motion
Move to adopt the contents of document /r0 into the P draft.
Technical (75%) Y: N: A:
Chris Trecker, Azimuth Systems
Pratik Mehta (Dell), et al