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Date: 2008-05-14

Update on 11n Greenfield Transmissions Causing False DFS Detects and Resolution of Related LB124 Comments. Authors:. Date: 2008-05-14. An update on latest tests providing realistic evidence of GF-DFS problem – Yet rejecting related CIDs for now….

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Date: 2008-05-14

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  1. Update on 11n Greenfield Transmissions Causing False DFS Detects and Resolution of Related LB124 Comments • Authors: • Date: 2008-05-14 Chan et al. (Cisco Systems)

  2. An update on latest tests providing realistic evidence of GF-DFS problem – Yet rejecting related CIDs for now… • TGn has been presented with evidence that GF transmissions can cause false radar detects on legacy 802.11a devices, creating unnecessary interruptions and lowering their throughputs • It’s revealed that there’re at least 2 different vendors with these problems • In LB 124, there are 10 CIDs from individuals of different companies that asks TGn to consider this issue and adapt the solution proposed in 08/0302r5 at the Mar 2008 Orlando meeting • Based on feedback received, we’ve improved this solution so that opposing viewpoints are included, i.e., it’s a better compromise. (See later slide 4.) • As TGn has originally planned to complete LB124 in July 2008, we had planned to bring forth this new compromise then • Kudos to members of TGn, comment resolution has moved forward rapidly and we are on schedule to motion for a new LB before end of this week! • However, we don’t believe we’ve obtained enough data or have enough time to explain this new compromise yet • But in the interest of moving forward so that TGn can go to LB, at this time we: • Provide an update on the new results that we have collected supporting the GF-DFS issue • Explain the new improved solution • Propose to rejectthese CIDs • (We will submit comments on this issue in the next TGn LB and we encourage those who submitted the same to do so again.) Chan et al. (Cisco Systems)

  3. Latest tests show GF interferer can cause false triggers to multi-tenant environments Solid wall between two sides of floor. • Same GF interferers as in 08/351r2 was placed at location “A” on the same floor • 11a APs at pink and red locations indicated DFS radar detects • Same GF interferer as in 08/351r2 was placed at location “A” on the floor above • 11a AP at red location indicated DFS radar detects • These 11a APs are at least several tens of feet and a solid wall or a solid floor away from the GF interferers! • This implies 11a users sharing a floor or on a nearby floor with GF users can be affected A ~30 ft This side of office being tested. Chan et al. (Cisco Systems)

  4. Proposing improved prevention mechanism that narrows scope of scenarios that requires protection • The proposed prevention mechanism is the same as that presented in 08/0302r5 but now: • Only applies to regulatory classes that are subject to DFS with 50-100 microsecond radar pulses • Only forbids GF frames of durations between 50 and 100 us • Effectively this applies only to the 5 GHz DFS bands in USA, Canada and Japan • Overview of prevention mechanism: • When HT GF AP detects a beacon from an 11a AP, if they are in a long-pulse DFS regulatory class, the HT GF network switches to disabling 50-100 us GF transmissions • No monitoring or scanning on clients at all • Monitoring of non-HT OBSS only on the AP • No client requirements other than changing their behavior according to AP’s beacon • No new fields but re-uses existing 11n bits and signaling schemes • Minor changes from D2.0 behavior • Preserves 11n GF evolution path • Achieves true definition of having a “greenfield”. Proposed text for this mechanism is in 08/0302r6. Anything but 50-100 us GF Anything but 50-100 us GF Beacon HT Greenfield AP Non-HT AP Chan et al. (Cisco Systems)

  5. Proposing to reject GF-DFS CIDs for now so 11n can move forward but continue discussion of this issue in the next LB • Reject CIDs 6181, 6326, 6073, 6196, 6137, 6074, 6304, 6231, 6179, 6067 with resolution text: • “Reject: The problem of false detections in legacy devices is not limited to GF receptions. TGn does not feel this is an issue to act upon until further evidence is provided.” Chan et al. (Cisco Systems)

  6. Backup slides Chan et al. (Cisco Systems)

  7. Vendor X (802.11a device) Vendor X (802.11a device) Latest tests with WiFi draft 11n testbed devices show GF-DFS problem is beyond theoretical and commonly occurs Test Setup: Neighboring APs in range but on different channels Vendor Y (HT Greenfield Client on laptop) Bi-directional VoIP streams WAN Radar Detects!!! Vendor Z (HT Greenfield AP) On a DFS Channel Vendor Y (HT Greenfield Client on laptop) Vendor X (802.11a device) 11a clients generating real over the air network traffic On a DFS Channel Chan et al. (Cisco Systems)

  8. Same intensity of false detects with different VoIP codecs and open real WLAN environment More details on the test and setup: • VoIP streams were generated by latest version of IxChariot, industry designated network traffic generation and testing tool for WiFi certifications • We used the G.711U codec used with default settings. • This is the most prevalent VoIP codec used in the industry • False radar triggers began shortly after VoIP traffic began, eg. within 5 minutes • Vendor X Legacy APs did not have any record of falsing for a long time before tests commenced or between tests Chan et al. (Cisco Systems)

  9. References • “Compliance Measurement Procedures for Unlicensed-national Information Infrastructure Devices Operating In The 5250-5350 Mhz and 5470-5725 Mhz Bands Incorporating Dynamic Frequency Selection”, Appendix to Revision of Parts 2 and 15 of the Commission’s Rules to Permit Unlicensed National Information Infrastructure (U-NII) devices in the 5 GHz band, FCC 06-96, June 30, 2006. • Submission 07/0329r2 • Submission 07/2849r0 • Submission 08/0111r2 • Submission 08/0301r0 • Submission 08/0302r5 • Submission 08/0351r2 Chan et al. (Cisco Systems)

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