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Real Air-time Occupation by Beacon and Probe

Real Air-time Occupation by Beacon and Probe. Authors:. Date: 2012-01-12. Abstract. This document shows retry numbers of Probe Response as the answer for discussion in Atlanta. (Slide 9). Motivation. 3G mobile operators have demand to offload their data traffics to WLAN network.

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Real Air-time Occupation by Beacon and Probe

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  1. Katsuo Yunoki, KDDI R&D Laboratories Real Air-time Occupation by Beacon and Probe Authors: • Date: 2012-01-12

  2. Katsuo Yunoki, KDDI R&D Laboratories Abstract • This document shows retry numbers of Probe Response as the answer for discussion in Atlanta. (Slide 9)

  3. Katsuo Yunoki, KDDI R&D Laboratories Motivation • 3Gmobile operators have demand to offload their data traffics to WLAN network. • Especially, they have higher demands for the locations where many people meet or stay for data offloading, because high data traffics occur at those locations. • It’s highly expected that FILS will realize transition from 3G to WLAN in very short time.

  4. Katsuo Yunoki, KDDI R&D Laboratories Real world (1) • Number of Smart-phone is increasing. • iPhone, Android, Windows-phone, Blackberry… • Smart-phone holders always touch its screen. • While its screen is activated (backlight turned on), Smart-phone starts searching surrounding WLAN-APs.

  5. Katsuo Yunoki, KDDI R&D Laboratories Real world (2) • Many Smart-phone holders are in the crowded commuter train. • Imagine what happens when the train arrives at the station. • Air monitoring was executed at a train station in Tokyo. Results are explained in the following slides.

  6. Katsuo Yunoki, KDDI R&D Laboratories Conditions • Time/Date: Around 18:00 / October 11(Tue), 2011 • Location: Shinjuku station (Keio line), Tokyo • Monitoring CH: 6CH(2,437MHz) • Monitoring period: 300 seconds (5 minutes) <Equipment> • Thinkpad X200 • Windows XP • USB Wireless Monitor Adoptor (Air Pcap NX) • Wireshark Measured CH

  7. Katsuo Yunoki, KDDI R&D Laboratories Result • Observed frames

  8. Katsuo Yunoki, KDDI R&D Laboratories Result (cont.) Frames Bytes • Time occupation is more important. • Doc. IEEE802.11-11/1031r0 was referred for time occupation analysis.

  9. Katsuo Yunoki, KDDI R&D Laboratories Transmission Rate

  10. Katsuo Yunoki, KDDI R&D Laboratories Transmission Rate (cont.)

  11. Katsuo Yunoki, KDDI R&D Laboratories Occupied Time Calculation (Beacon) Occupied Time Beacon DIFS CW TX TIME • aSlotTime: 20us • aSIFSTime: 10us • aPreambleLength: 144us • aPLCPHeaderLength: 48bits • aCWmin: 31 • aCWmax: 1023 • DIFS: 50us • CW: 310us Occupied Time = ∑((DIFS + CW + aPreambleLength + aPLCPHeaderLength/DATARATE) * TotalFrames + (TotalBytes * 8/DATARATE)) = ((50 + 310 + 144 + 48 / 1.0) * 13,861 + (1,688,640 * 8 / 1.0) + ((50 + 310 + 144 + 48 / 11.0) * 2 + (80 * 8 / 11.0) + ((50 + 310 + 144 + 48 / 24.0) * 7 + (280 * 8 / 24.0) + ((50 + 310 + 144 + 48 / 54.0) * 1 + (40 * 8 / 54.0) = 21,165,613 us (7.06%)

  12. Katsuo Yunoki, KDDI R&D Laboratories Occupied Time Calculation (Probe Request) Occupied Time Probe Request DIFS CW TX TIME Occupied Time = ∑((DIFS + CW + aPreambleLength + aPLCPHeaderLength/DATARATE) * TotalFrames + (TotalBytes * 8/DATARATE)) = ((50 + 310 + 144 + 48 / 1.0) * 6,547 + (838,510 * 8 / 1.0) + ((50 + 310 + 144 + 48 / 2.0) * 21 + (10,019 * 8 / 2.0) + ((50 + 310 + 144 + 48 / 5.5) * 13 + (12,633 * 8 / 5.5) + ((50 + 310 + 144 + 48 / 6.0) * 2 + (1,590 * 8 / 6.0) + ((50 + 310 + 144 + 48 / 9.0) * 3 + (2,631 * 8 / 9.0) + ((50 + 310 + 144 + 48 / 11.0) * 510 + (76,565 * 8 / 11.0) + ((50 + 310 + 144 + 48 / 12.0) * 2 + (3,060 * 8 / 12.0) + ((50 + 310 + 144 + 48 / 18.0) * 7 + (10,198 * 8 / 18.0) + ((50 + 310 + 144 + 48 / 24.0) * 4 + (3,154 * 8 / 24.0) + ((50 + 310 + 144 + 48 / 48.0) * 10 + (13,509 * 8 / 48.0) + ((50 + 310 + 144 + 48 / 54.0) * 20 + (17,928 * 8 / 54.0) = 10,754,454us (3.58%)

  13. Katsuo Yunoki, KDDI R&D Laboratories Occupied Time Calculation (Probe Response) Occupied Time Probe Response ACK DIFS CW TX TIME SIFS TX TIME • aSlotTime: 20us • aSIFSTime: 10us • aPreambleLength: 144us • aPLCPHeaderLength: 48bits • aCWmin: 31 • aCWmax: 1023 • DIFS: 50us • CW: 310us • ACKRate: 1Mbps • ACKLength: 14Bytes

  14. Katsuo Yunoki, KDDI R&D Laboratories Occupied Time Calculation (Probe Response)(Cont.) Occupied Time = ∑((DIFS + CW + aPreambleLength + aPLCPHeaderLength/DATARATE +aSIFSTime + aPreambleLength + aPLCPHeaderLeangth / ACKRATE + ACKLength * 8 / ACKRATE) * TotalFrames + (TotalBytes * 8/DATARATE)) = ((50 + 310 + 144 + 48 / 1.0 +10+ 144+48/1.0+14*8/1.0) * 24,606 + (2,849,896 * 8 / 1.0) + ((50 + 310 + 144 + 48 / 2.0 + 10+144+48/1.0+14 * 8 / 1.0) * 4 + (5,257 * 8 / 2.0) + ((50 + 310 + 144 + 48 / 5.5 + 10+144+48/1.0+14 * 8 / 1.0) * 7 + (10,710 * 8 / 5.5) + ((50 + 310 + 144 + 48 / 6.0 + 10+144+48/1.0+14 * 8 / 1.0) * 1 + (1,530 * 8 / 6.0) + ((50 + 310 + 144 + 48 / 9.0 + 10+144+48/1.0+14 * 8 / 1.0) * 1 + (1,530* 8 / 9.0) + ((50 + 310 + 144 + 48 / 11.0 + 10+144+48/1.0+14 * 8 / 1.0) * 15+ (13,848 * 8 / 11.0) + ((50 + 310 + 144 + 48 / 12.0 + 10+144+48/1.0+14 * 8 / 1.0) * 4 + (6,120 * 8 / 12.0) + ((50 + 310 + 144 + 48 / 18.0 + 10+144+48/1.0+14 * 8 / 1.0) * 7 + (8,212 * 8 / 18.0) + ((50 + 310 + 144 + 48 / 24.0 + 10+144+48/1.0+14 * 8 / 1.0) * 6 + (5,279 * 8 / 24.0) + ((50 + 310 + 144 + 48 / 36.0 + 10+144+48/1.0+14 * 8 / 1.0) * 3 + (4,590 * 8 / 36.0) + ((50 + 310 + 144 + 48 / 48.0 + 10+144+48/1.0+14 * 8 / 1.0) * 2 + (2,259 * 8 / 48.0) + ((50 + 310 + 144 + 48 / 54.0 + 10+144+48/1.0+14 * 8 / 1.0) * 31 + (32,100 * 8 / 54.0) = 44,215,439us (14.74%)

  15. Katsuo Yunoki, KDDI R&D Laboratories Occupied Time Calculation Result

  16. Katsuo Yunoki, KDDI R&D Laboratories Retry of Probe Response • Probe Response frames: 24,687 • Retry frames in these: 12,274 (49.7%) • Almost all retry frames are transmitted in a few msec after the original transmission. • The percentage of retry frames may be increased in more congested situation. • See Slide 17 for detailed example.

  17. Katsuo Yunoki, KDDI R&D Laboratories Example of retry frames(Probe Response) Sequence Number Retry Retry Retry Retry Retry Retry Retry Retry Retry Retry Retry

  18. Example of Active Scanning(Probe Request) This is my personal smart-phone  Multiple shots of Probe request were transmitted for a timing. It may be vender implementation. The second timing is around timestamp=8.00.

  19. Katsuo Yunoki, KDDI R&D Laboratories Considerations(Opinion) • Multiple shots of Probe request were transmitted every some seconds. Because the STA didn’t know any SSIDs from surrounding APs. • If the STA were in the area of the target AP, the STA would receive Beacons from the AP before sending Probe requests at the second timing. • Active scanning with wildcard SSID shall be just for the first shots. • Repetition of sending Probe requests isn’t effective. It only brings packet congestion.

  20. Katsuo Yunoki, KDDI R&D Laboratories Conclusion • Because of WLAN enabled devices increasing, especially Smart-phones, WLAN air circumstances are getting more crowded. • In this packet monitoring, probe responses existed 5 times more than probe requests. • Retry transmissions of Probe Response are frequently happened. • Repetition of Probe requests is not effective. It brings packet congestion. • To see the benefits of effective FILS, improvement of air circumstances would be needed by reducing unnecessary packet exchanges.

  21. Katsuo Yunoki, KDDI R&D Laboratories References • doc. IEEE802.11-11/1031r0

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