1. doc.: IEEE 802.11-04/0748r0 Submission July 2004 Spilman, Azimuth Systems Test Methodology for Measuring BSS Transition Time Jeremy Spilman Azimuth Systems jeremy_spilman@azimuthsystems.com

2. doc.: IEEE 802.11-04/0748r0 Submission July 2004 Spilman, Azimuth Systems Outline Methodology Topology Procedure Results

3. doc.: IEEE 802.11-04/0748r0 Submission July 2004 Spilman, Azimuth Systems Why define test methodology? Can be a selection criteria for proposals in TGr Highlights issues with current standard A test methodology can be used for real world testing as well as a theoretical analysis –Allows apples-to-apples comparisons –But must be based on observable events

4. doc.: IEEE 802.11-04/0748r0 Submission July 2004 Spilman, Azimuth Systems Different ways to cause a roam Rolling cart Power off AP “Cone of Silence” RF Attenuators –Open Air –Controlled Environment

5. doc.: IEEE 802.11-04/0748r0 Submission July 2004 Spilman, Azimuth Systems 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

6. doc.: IEEE 802.11-04/0748r0 Submission July 2004 Spilman, Azimuth Systems Controlled Environment Topology Combiner Wireless Sniffer Combiner Wireless Sniffer Ethernet Hub Ethernet Sniffer Traffic Source / Sink

7. doc.: IEEE 802.11-04/0748r0 Submission July 2004 Spilman, Azimuth Systems Device Topology 2 APs, 1 Client, 1 Server 2 Wireless Protocol Analyzers – Positioned between each AP and Client 1 Ethernet Sniffer Packets Captured on: –Both AP Channels –Wired Ethernet on Server Traffic generated between Client and Server

8. doc.: IEEE 802.11-04/0748r0 Submission July 2004 Spilman, Azimuth Systems 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

9. doc.: IEEE 802.11-04/0748r0 Submission July 2004 Spilman, Azimuth Systems Packet Capture On Wired Ethernet: –Last Data Packet before Roam –First Data Packet after Roam On Wireless Protocol Analyzers –Above packets, plus: –802.11 Management frames sent during roam

10. doc.: IEEE 802.11-04/0748r0 Submission July 2004 Spilman, Azimuth Systems Key packets during a roam Some intervals may not exist Last Unack’d Data t RETRY Last Ack’d Data t SCAN t ASSOCIATE t DATA First Probe Request First Beacon Auth Request Auth Response Assoc Request Assoc Response First Ack’d Data

11. doc.: IEEE 802.11-04/0748r0 Submission July 2004 Spilman, Azimuth Systems Client Association: First data packet after roam Stimulating a Transition t RETRY t SCAN Last data packet before roam t ASSOCIATE t ROAM t DATA AP1AP2 max min Atten AP1 AP2 Attenuator Sweep Time Inter-Roam Delay

12. doc.: IEEE 802.11-04/0748r0 Submission July 2004 Spilman, Azimuth Systems Test Results, Total Roam Time

13. doc.: IEEE 802.11-04/0748r0 Submission July 2004 Spilman, Azimuth Systems Test Results, Transition Intervals

14. doc.: IEEE 802.11-04/0748r0 Submission July 2004 Spilman, Azimuth Systems Conclusion Repeatability and flexibility of controlled environment is very beneficial Capturing 802.11 management packets gives visibility into underlying performance variations