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doc.: IEEE /0757r0 Submission July 2005 C Trecker, Azimuth SystemsSlide 3 Outline Definitions and Metrics Methodology Topology Procedure Results
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July 2005
C Trecker, Azimuth Systems
Slide 1
doc.: IEEE 802.11-05/0757r0
Submission
Test Methodology for measuring Fast BSS Transition Performance
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: 2005-07-20
Name Company Address Phone email Chris Trecker Azimuth
Systems 31 Nagog Park, Acton, MA 01720
(978) 263-6610 [email protected]
Authors:
July 2005
C Trecker, Azimuth Systems
Slide 2
doc.: IEEE 802.11-05/0757r0
Submission
Abstract
This presentation proposes test metrics and test methodologies to characterize fast BSS transition performance.
July 2005
C Trecker, Azimuth Systems
Slide 3
doc.: IEEE 802.11-05/0757r0
Submission
Outline• Definitions and Metrics• Methodology• Topology• Procedure• Results
July 2005
C Trecker, Azimuth Systems
Slide 4
doc.: IEEE 802.11-05/0757r0
Submission
Definitions and Metrics• Fast BSS Handshake Time: Time between FBT Auth Request and
FBT (Re) Assoc Response (Base Mechanism). When pre-reservation is used, time between FBT (Re) Association Request and FBT (Re) Association Response.
– This time can be precisely measured.
• Fast BSS Transition Time. Time between MSDU delivery to DS from AP1 and AP2 as a STA executes a FBT transition from AP1 to AP2. Should also measure the time downstream DS – STA MSDU time.
– This time is measured both on the DS (FBT Time DS) and on the air (FBT Time Air)
– This time can not be precisely measured unless using WIFI test equipment configured to act as a STA in a controlled environment.
– This time will generally be measured statistically over several transitions at different data rates.
July 2005
C Trecker, Azimuth Systems
Slide 5
doc.: IEEE 802.11-05/0757r0
Submission
Fast BSS Handshake Time
Observed BSS Transition Time
FBT Handshake Time
Auth Req Auth Resp Assoc Req Assoc Resp
packets observed on the air
July 2005
C Trecker, Azimuth Systems
Slide 6
doc.: IEEE 802.11-05/0757r0
Submission
Fast BSS Transition Time
MSDU-AP1 ACK
Last possible instant where frames can pass through old
AP
MSDU-AP2 ACK
First possible instant where frames can pass through new
AP
Theoretical BSS Transition
Time. . . . . .
Observed FBT Time on air
packets observed on the air
MSDU-AP1 MSDU-AP2
. . .packets observed on the DS
Observed FBT Time on DS
July 2005
C Trecker, Azimuth Systems
Slide 7
doc.: IEEE 802.11-05/0757r0
Submission
Methodology• Force a Fast BSS Transition
– Base Mechanism– Pre-reservation
• Measure Fast BSS Handshake• Measure Fast BSS Transition on DS and
over the air• Iterate to allow for statistical aberrations• Use different data rates.• This allows for apples-to-apples
comparisons in FBT performance
July 2005
C Trecker, Azimuth Systems
Slide 8
doc.: IEEE 802.11-05/0757r0
Submission
Different ways to cause a fast-BSS Transition
• STA or AP initiated for reasons other than a degrading RF signal
• Rolling cart• Power off AP• “Cone of Silence”• RF Attenuators
– Open Air– Controlled Environment
July 2005
C Trecker, Azimuth Systems
Slide 9
doc.: IEEE 802.11-05/0757r0
Submission
Use cases require controlled environment
• Both APs always on• Must control amount of BSS overlap• Figure 1 implies client moves between BSSs smoothly• Methodology must be flexible for additional use cases
July 2005
C Trecker, Azimuth Systems
Slide 10
doc.: IEEE 802.11-05/0757r0
Submission
Controlled Environment Topology
Combiner
WirelessSniffer
Combiner
WirelessSniffer
EthernetHub
Ethernet SnifferTraffic Source / Sink
July 2005
C Trecker, Azimuth Systems
Slide 11
doc.: IEEE 802.11-05/0757r0
Submission
Device Topology• 2 APs, 1 Client, 1 Server• 2 Wireless Protocol Analyzers
– Positioned between each AP and Client• 1 Ethernet Sniffer (assumes DS is ethernet)
• Packets Captured on:– Both AP Channels– Wired Ethernet on Server
• Traffic generated between Client and Server
July 2005
C Trecker, Azimuth Systems
Slide 12
doc.: IEEE 802.11-05/0757r0
Submission
Controlling Path Loss• Each station is cabled into a shielded
chamber– Greater than 120 dB isolation required between
station and AP to guarantee loss of association• Path loss between stations is
controlled programmatically with step attenuators– Dynamic range of 80dB is sufficient
July 2005
C Trecker, Azimuth Systems
Slide 13
doc.: IEEE 802.11-05/0757r0
Submission
Packet Capture• On Wired DS:
– Last Data Packet before Roam from AP1– First Data Packet after Roam from AP2
• On Wireless Protocol Analyzers– Above packets, plus:– 802.11 Management frames to measure FBT handshake.
July 2005
C Trecker, Azimuth Systems
Slide 14
doc.: IEEE 802.11-05/0757r0
Submission
Client Association:
First data packetafter roam
Stimulating a Transition
t PRE-RES t RETRY
Last data packetbefore roam
t FT
t ROAM
t DATA
AP1 AP2
max
min
Atten
AP1
AP2
Attenuator Sweep Time
Inter-Roam Delay
July 2005
C Trecker, Azimuth Systems
Slide 15
doc.: IEEE 802.11-05/0757r0
Submission
Test Results, Total Roam Time
0
2
4
6
8
10
12
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39Test Iteration
Tota
l Roa
m T
ime
(s)
July 2005
C Trecker, Azimuth Systems
Slide 16
doc.: IEEE 802.11-05/0757r0
Submission
Conclusion• Fast BSS Transition Performance metrics will
allow for valid comparisons between different implementation algorithms and vendor solutions
• Repeatability and flexibility of controlled environment is very beneficial
• Valid system FBT performance measurement will depend on statistical analysis