doc.: ieee 802.11-06-0005-01-000t submission jan 2006 chris trecker, azimuth systemsslide 1 test...

Jan 2006

Chris Trecker, Azimuth SystemsSlide 1

doc.: IEEE 802.11-06-0005-01-000t

Submission

Test Methodology for Measuring Loss, Delay and Jitter

Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

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Date: 2006-01-9

Name Company Address Phone email Chris Trecker Azimuth Systems, Inc 31 Nagog Park,

Acton, MA 01720 (978) 268-9205 chris_trecker@azimuthsys

tems.com Fanny Mlinarsky

Azimuth Systems, Inc. 31 Nagog Park, Acton, MA 01720

(978) 268-9205 [email protected]

Authors:

Jan 2006


doc.: IEEE 802.11-06-0005-01-000t

Submission

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.

Jan 2006


doc.: IEEE 802.11-06-0005-01-000t

Submission

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

Jan 2006


doc.: IEEE 802.11-06-0005-01-000t

Submission

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

Packet 1 Packet 2 Packet 4

Jan 2006


doc.: IEEE 802.11-06-0005-01-000t

Submission

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.

Transmitter

Data Network

Receiver

packet is transmitted

packet is received

Packet Latency

Jan 2006


doc.: IEEE 802.11-06-0005-01-000t

Submission

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 6.3.1 of RFC 1889 for interarrival jitter.

Packet Transmission:

10 ms

Packet 1 Packet 2 Packet 3 Packet 4

10 ms 10 ms

Packet Reception:

11 ms

Packet 1 Packet 2 Packet 3 Packet 4

9 ms 11 ms

Jan 2006


doc.: IEEE 802.11-06-0005-01-000t

Submission

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 6.3.1 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.

Jan 2006


doc.: IEEE 802.11-06-0005-01-000t

Submission

STA Test Configuration

Latency-Sensitive Traffic

802.11 Traffic Analyzer

STA UTAETE or

off-the-shelf AP

RF CablesVariableAttenuator

Legend:

AETE – AP Emulation Test Equipment

Jan 2006


doc.: IEEE 802.11-06-0005-01-000t

Submission

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.

Jan 2006


doc.: IEEE 802.11-06-0005-01-000t

Submission

AP Test Configuration

SETE-2 or additional

802.11 STAs

802.11 and DS Traffic

Analyzer

DS Traffic Generator (optional)

AP / UT

SETE-1 or 802.11 STA (i.e., VOIP

phone)


Background and Latency-Sensitive

Traffic

Application Node (i.e.,

VOIP phone)


Background and Latency-Sensitive

Traffic Application Specific Server

(i.e., VOIP server) if applicable

RF cables

VariableAttenuator

Legend: Wired LAN cables

SETE – Station Emulation Test Equipment

Jan 2006


doc.: IEEE 802.11-06-0005-01-000t

Submission

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 802.11 and DS traffic analyzers must have synchronized time-stamps in order to properly calculate packet latency.

Jan 2006


doc.: IEEE 802.11-06-0005-01-000t

Submission

Packet Loss Results from VOIP Test

Jan 2006


doc.: IEEE 802.11-06-0005-01-000t

Submission

Packet Delay Results from VOIP Test

Jan 2006


doc.: IEEE 802.11-06-0005-01-000t

Submission

Packet Jitter Results from VOIP Test

Jan 2006


doc.: IEEE 802.11-06-0005-01-000t

Submission

Motion

Move to adopt the contents of document 11-06-0004/r0 into the P802.11.2 draft.

Technical (75%)

Y:

N:

A:

doc.: ieee 802.11-06-0005-01-000t submission jan 2006 chris trecker, azimuth systemsslide 1 test...

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