doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 1 VoIP Traffic by Draft-n Greenfield Devices Causes False RADAR Detection on DFS Channels Date: Authors:

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 2 Straw polls have previously shown support to change 11n to avoid radar issues caused by GF In LB 97 (Draft 1.0), there were CIDs which pointed out that GF transmissions can be falsely detected by legacy devices in the DFS band as radar We performed experiments and presented a submission, 07/0329r2, in March 2007 (Orlando) to discuss the results We showed that a widely used receiver hardware gave false positive radar detects for VoIP traffic using Greenfield mode Strawpolls showed a significant fraction of the TGn Coex Ad Hoc members are concerned with this problem, but more investigations should be done to be certain Subsequently, we performed a set of measurements with another legacy 11a receiver and presented them in submission 07/2849r0 in Nov 2007 (Atlanta) Again, false positive radar detects are observed for VoIP traffic using Greenfield mode Strawpoll showed an even more significant fraction of the TGn Coex Ad Hoc members – a majority – agreeing for a text change to address this

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 3 The GF-DFS problem is an industry-wide a problem Since then weve continued to perform testing with various 11a chipsets and vendors DFS implementations In our analysis, we also found that the bin-5 radar profile which is part of the current FCC DFS certification strongly resembles a GF voice detector – thus this is a widespread problem Our tests have shown at least two different 11a chipsets and at least two different vendors that would have falsing issues due to software generated GF VoIP transmissions In our latest tests, we went further and employed WiFi Draft n testbed devices and actual mixed data and VoIP traffic network traffic. The results showed these GF transmissions unmistakably and consistently caused an 11a device to trigger radar detects.

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 4 Latest tests with WiFi draft 11n testbed devices show GF-DFS problem is beyond theoretical Vendor Z (HT Greenfield AP) Test Setup Vendor Y (HT Greenfield Client on laptop) Vendor Y (HT Greenfield Client on laptop) Vendor X (802.11a device) All devices on Channel 52 (a DFS channel) Experiment performed in screen room. Two bi-directional VoIP streams and ping traffic Radar detects

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 5 More details on the test setup: VoIP streams were generated by IxChariot, industry designated network traffic generation and testing tool for WiFi certifications Voice codec used was G.711U with default settings: Test performed with MCS 3, 4, 5, 6, 7 and 15. False radar triggers began on every trial shortly after VoIP traffic began, eg. less than 5 minutes Results did not change when laptop clients were loaded with ping traffic Radar triggers with various test setup show GF-DFS is easy to occur and consistent

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 6 Sample screen shot of Chariot VoIP test

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 7 Detrimental consequences expected from GF on DFS Bands Operations of legacy a networks which have no concept of Greenfield mode would be disrupted by their false detects from GF transmissions by moving to another channel each time Many mesh network architectures use the 5 GHz band for backhaul A single voice call using GF transmissions could bring down a mesh tree while it changes channel. A small number of GF APs using efficient channel selection can totally occupy the 5 GHz band and cause a mesh network outage. This type of behavior also facilitates possibilities of simple denial of service attacks There is nothing in the DFS regulations that indicate radar may be ignored if preceded by MAC protection. Therefore protection is ineffective for GF preambles in DFS bands.

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide n should be changed to prevent GFs potentially disruptive effects to legacy 11a devices in the DFS bands Therere two options to solving this problem: 1. Prohibit Greenfield operations in DFS bands or 2. Define a suitable mechanism to prevent Greenfield operation in DFS bands in the presence of legacy 11a devices –Simple to implement since it reuses existing 11n schemes to signal when GF can be used. –Involves only a software upgrade/change. –More importantly, this mechanism doesnt affect 11n GF evolution path, as 11a devices get phased out in the next few years, GF wouldnt be prevented from use due to this prohibition. –True to the definition of having a greenfield. Preferred

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 9 Illustration of Option 2s proposed mechanism: AP detects non-HT OBSS (1/4) HT Greenfield AP Operation on a DFS Band Non-HT AP Beacon During operations or when establishing a BSS, an HT Greenfield AP receives beacon from a non-HT AP, thus detecting a non-HT OBSS. HT Greenfield Transmissions HT Greenfield Clients HT Greenfield Transmissions Covered by proposed text changes in 08/0302r0.

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 10 Illustration of Option 2s proposed mechanism: AP detects non-HT OBSS (2/4) HT Greenfield AP Operation on a DFS Band Non-HT AP Beacon HT Greenfield AP sets its Greenfield support bit from 1 to 0 and OBSS Non-HT STAs Present bit from 0 to 1. HT Capabilities Info Field Greenfield bit: 1 0 Covered by proposed text changes in 08/0302r0. HT Infomration Element OBSS Non-HT STAs Present 0 1

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 11 Illustration of Option 2s proposed mechanism: AP detects non-HT OBSS (3/4) HT Greenfield AP Operation on a DFS Band Non-HT AP Beacon Greenfield transmissions are then suppressed across this BSS. Non-HT OBSS is not disrupted by 11n BSS. HT Mixed Mode Transmissions HT Greenfield Clients HT Mixed Mode Transmissions Covered by proposed text changes in 08/0302r0.

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 12 Illustration of Option 2s proposed mechanism: AP detects non-HT OBSS (4/4) HT Greenfield AP Operation on a DFS Band Non-HT AP If non-HT AP does not exist anymore, HT Greenfield AP can revert to its previous settings after thirty minutes HT Capabilities Info Field Greenfield bit: 0 1 After waiting 30 min… Covered by proposed text changes in 08/0302r0. HT Infomration Element OBSS Non-HT STAs Present 1 0

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 13 Option 2 solution resolves three comments: CIDCommen ter Type of Comment Part of No Vote ClauseCommentProposed ChangeResolution 5123Chan, Douglas TY9.13.3Transmission of GF preambles in DFS bands can cause DFS false alarms on legacy STAs. Thre is nothing in the DFS regulations that indicate radar may be ignored if preceded by MAC protection. Therefore protection is ineffective for GF preambles in DFS bands. Prohibit GF in DFS bands. Accept; as in editor instructions in submission 08/0302r Stephens on, Dave 5363Hart, Brian LB 115 (Draft 3.0) comments:

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 14 Strawpoll Task Group n should design the specification to appropriately account for and prevent GFs potential disruptive effects to legacy 11a devices in the DFS bands. Accept the resolutions proposed for CIDs 5123, 5363 and 5795 in 08/301r0, i.e. the draft text changes with editor instructions in 08/0302r0. Yes No Abstain

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 15 References Compliance Measurement Procedures for Unlicensed-national Information Infrastructure Devices Operating In The Mhz and Mhz Bands Incorporating Dynamic Frequency Selection, Appendix to Revision of Parts 2 and 15 of the Commissions Rules to Permit Unlicensed National Information Infrastructure (U-NII) devices in the 5 GHz band, FCC 06-96, June 30, Submission 07/0329r2 Submission 07/2849r0 Submission 08/0111r2

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 16 Backup slides

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 17 Excerpted from Nov 2007 (Atlanta) Coex Ad Hoc Minutes:

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 18 Recap of previous investigations on this issue

doc.: IEEE /0301r0 Submission March 2008 Chan et al. (Cisco Systems) Slide 19 Recap of previous investigations on this issue