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Greenfield VoIP Transmissions Cause

VIEWS: 11 PAGES: 19

									March 2008                                                              doc.: IEEE 802.11-08/0351r0
 New Evidence that 11n Greenfield Devices Causes
 False RADAR Detections on DFS Channels
                                        Date: 2008-03-17
Authors:
Name               Affiliation       Address                     Phone             email
Douglas Chan       Cisco Systems     170 West Tasman Drive,      408-527-9344      dougchan@cisco.com
                                     San Jose, CA 95134
Lian Jiang         Cisco Systems     170 West Tasman Drive,      408-853-1899      liajiang@cisco.com
                                     San Jose, CA 95134
Brian Hart         Cisco Systems     170 West Tasman Drive,      408-525-3346      brianh@cisco.com
                                     San Jose, CA 95134
Luke Qian          Cisco Systems     4125 Highlander Parkway     330-523-2051      lchia@cisco.com
                                     Richfield , OH 44286
Jan Kruys          Cisco Systems     Haarlerbergpark,            +31-20-357-2447   jkruys@cisco.com
                                     Haarlerbergweg 13-19,
                                     Amsterdam, Netherlands
                                     1101 CH
Malik Audeh        Tropos Networks   555 Del Rey Ave             408-331-6835      audeh@tropos.com
                                     Sunnyvale, CA 94085
Jorjeta Jetcheva   Firetide, Inc.    16795 Lark Ave, Suite 200   408-355-7215      jjetcheva@firetide.com
                                     Los Gatos, CA 9503
Stephen Rayment    BelAir Networks   603 March Road              613-254-7070      srayment@belairnetworks
                                     Kanata ON Canada            x112              .com
                                     K2K 2M5
Peter Loc          Marvell

Tomo Adachi        Toshiba




Submission                                            Slide 1                              Chan et al. (Cisco Systems)
March 2008                                            doc.: IEEE 802.11-08/0351r0
 Latest tests provide conclusive evidence that Greenfield
 causes false detects in 11a devices on DFS channels

 • Since D2.0, we’ve presented tests that showed Greenfield transmissions can
   cause false detects in 11a devices on DFS channels
   − 07/0329r2 (Mar 2007) and 07/2849r0 (Nov 2007) showed software MATLAB
     generated GF signals and those of VoIP traffic patterns cause false detects on
     11a devices from different vendors
   − There were questions if this issue exists with GF transmissions by actual 11n
     hardware
 • So we performed tests with real VoIP traffic on WiFi certified Draft 11n Testbed
   devices and observed the same intensity of false detects
   − This is documented in 08/0301r1 and presented at the TGn pre-meeting last
     week
   − Because these tests involved one VoIP codec and were performed in a screen
     room, there were questions whether the codec was cherry-picked and whether
     the screen room represented real-world environment
 • Over the weekend, we performed the same tests with multiple different VoIP
   codecs and also on an open-space of an operating 11a deployed network
   − We observed the SAME INTENSITY of false detects on 11a devices
 • These new evidences dispels any uncertainty previously casted on by doubters
 • We can safely conclude that GF on DFS is indeed a real and common
   problem
Submission                              Slide 2                    Chan et al. (Cisco Systems)
      March 2008                                                                 doc.: IEEE 802.11-08/0351r0
       Latest tests with WiFi draft 11n testbed devices show GF-DFS
       problem is beyond theoretical and commonly occurs
     Test Setup:                                                                                    Neighboring APs in range
                                                    Vendor Y                          Vendor X      but on different channels
                                             (HT Greenfield Client                    (802.11a
                                                                                       device)
                                                    on laptop)


                                                                                                                        Vendor X
                                                                                                                        (802.11a
                              Bi-directional VoIP                                                  WAN                   device)

    Vendor Z                        streams

(HT Greenfield AP)
                                                                   Radar Detects!!!
   Channel 52




                          Vendor Y
                     (HT Greenfield Client
                                                                               Vendor X
                          on laptop)                                                                   11a clients generating real
                                                                           (802.11a device)
                                                                                                       over the air network traffic
                                                                               Channel 52


      Submission                                               Slide 3                           Chan et al. (Cisco Systems)
March 2008                                         doc.: IEEE 802.11-08/0351r0

 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 IxChariot, industry designated network
   traffic generation and testing tool for WiFi certifications
 • Codec used include G.711U, G.723.1 (MPMLQ), G.723.1 (ACELP) and
   G.726 with default settings.
   − These codecs are very different and have large range of variations in
     their parameters, eg. packet size in bytes and time, interpacket
     spacing. (see backup slide for details)
 • Tests performed with various MCS (eg. 3, 4, 5, 6, 7 and 15)
 • False radar triggers began on every trial shortly after VoIP traffic began,
   eg. within 5 minutes
 • Results did not change when laptop clients were loaded with ping traffic
 • Vendor X Legacy APs did not have any record of falsing before tests
   commenced or between tests

Submission                             Slide 4                 Chan et al. (Cisco Systems)
March 2008                         doc.: IEEE 802.11-08/0351r0

 Sample screen shot of Chariot VoIP test




Submission               Slide 5              Chan et al. (Cisco Systems)
March 2008                                          doc.: IEEE 802.11-08/0351r0

 Detrimental consequences expected from GF on
 DFS Bands

 • Operations of legacy 802.11a 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.

Submission                             Slide 6                   Chan et al. (Cisco Systems)
March 2008                                             doc.: IEEE 802.11-08/0351r0

 GF on DFS problem is not a late-breaking issue and
 is an industry-wide 802.11 concern
 • 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
   − 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
 • We performed a set of measurements with another legacy 11a receiver and
   presented them in submission 07/2849r0 in Nov 2007 (Atlanta)
   − Strawpoll showed an even more significant fraction of the TGn Coex Ad Hoc
     members – a majority – agreeing for a text change to address this
 • We hypothesized and presented in Feb 2008 telecon with 08/0111r2 that the
   problem may be related to DFS requirement for detecting the bin-5 radar profile
 • Now we show compelling and conclusive evidence of this problem
 • Overall 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
   − This problem may not be limited to VoIP traffic
   − This is an industry-wide 802.11 concern

Submission                               Slide 7                     Chan et al. (Cisco Systems)
 March 2008                                          doc.: IEEE 802.11-08/0351r0
  802.11n should be changed to prevent GF’s potentially
  disruptive effects to legacy 11a devices in the DFS bands

      • There’re 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 doesn’t affect 11n GF
Preferred         evolution path, as 11a devices get phased out in the next few
                  years, GF wouldn’t be prevented from use due to this
                  prohibition.
                – True to the definition of having a “greenfield”.


 Submission                            Slide 8                    Chan et al. (Cisco Systems)
March 2008                                                          doc.: IEEE 802.11-08/0351r0

 Illustration of Option 2’s proposed mechanism:
 AP detects non-HT OBSS (1/4)
   Operation on a DFS Band
                                                                       Covered by proposed text
                                                                        changes in 08/0302r0.


                                     HT Greenfield
                                     Transmissions


             HT Greenfield
             Transmissions                                 Beacon



                                     HT Greenfield                          Non-HT AP
                                         AP
                     HT Greenfield
                        Clients




                                               During operations or when establishing a BSS,
                                                an HT Greenfield AP receives beacon from a
                                                 non-HT AP, thus detecting a non-HT OBSS.




Submission                                       Slide 9                          Chan et al. (Cisco Systems)
March 2008                                                               doc.: IEEE 802.11-08/0351r0

 Illustration of Option 2’s proposed mechanism:
 AP detects non-HT OBSS (2/4)
   Operation on a DFS Band
                                                                            Covered by proposed text
                                                                             changes in 08/0302r0.

             HT Capabilities Info Field



                Greenfield bit:

                    1        0                                  Beacon



                                          HT Greenfield                          Non-HT AP
                                              AP
              HT Information Element



             OBSS Non-HT STAs Present

                    0        1                      HT Greenfield AP sets its Greenfield support
                                                      bit from 1 to 0 and OBSS Non-HT STAs
                                                              Present bit from 0 to 1.




Submission                                           Slide 10                          Chan et al. (Cisco Systems)
March 2008                                                              doc.: IEEE 802.11-08/0351r0

 Illustration of Option 2’s proposed mechanism:
 AP detects non-HT OBSS (3/4)
   Operation on a DFS Band
                                                                           Covered by proposed text
                                                                            changes in 08/0302r0.


                                     HT Mixed Mode
                                     Transmissions


             HT Mixed Mode
             Transmissions                                     Beacon



                                      HT Greenfield                             Non-HT AP
                                          AP
                     HT Greenfield
                        Clients




                                                 Greenfield transmissions are then suppressed
                                                                across this BSS.
                                                      Non-HT OBSS is not disrupted by 11n BSS.




Submission                                       Slide 11                             Chan et al. (Cisco Systems)
March 2008                                                           doc.: IEEE 802.11-08/0351r0

 Illustration of Option 2’s proposed mechanism:
 AP detects non-HT OBSS (4/4)
   Operation on a DFS Band
                                                                          Covered by proposed text
                                                                           changes in 08/0302r0.
                  After waiting 30 min…



             HT Capabilities Info Field



                Greenfield bit:

                    0        1            HT Greenfield                         Non-HT AP
                                              AP
              HT Infomration Element



             OBSS Non-HT STAs Present

                    1        0                     If non-HT AP does not exist anymore, HT Greenfield AP can
                                                         revert to its previous settings after thirty minutes




Submission                                           Slide 12                         Chan et al. (Cisco Systems)
March 2008                                     doc.: IEEE 802.11-08/0351r0

 Proposed prevention mechanism is simple and low
 impact to existing 11n implementations
     Merits of the proposed prevention mechanism
     • Simple to implement and deploy via a software upgrade
       − No monitoring or scanning on clients at all
       − Monitoring of non-HT OBSS only on the AP
       − Nothing required of clients other than changing their
         behavior according to AP’s beacon (which is a default
         behavior for 11n STAs) and not using GF for DLS etc if AP
         disables GF
       − 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”.

Submission                         Slide 13                 Chan et al. (Cisco Systems)
March 2008                                           doc.: IEEE 802.11-08/0351r0

 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 08/0302r0




Submission                             Slide 14                    Chan et al. (Cisco Systems)
March 2008                   doc.: IEEE 802.11-08/0351r0




             Backup slides




Submission        Slide 15              Chan et al. (Cisco Systems)
March 2008                                                            doc.: IEEE 802.11-08/0351r0

 Default Parameters of VoIP Codecs show large
 variations




   Excerpted from http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080094ae2.shtml
Submission                                         Slide 16                          Chan et al. (Cisco Systems)
March 2008                             doc.: IEEE 802.11-08/0351r0
 Excerpted from Nov 2007 (Atlanta) Coex Ad Hoc Minutes:




Submission                  Slide 17              Chan et al. (Cisco Systems)
March 2008                          doc.: IEEE 802.11-08/0351r0

 Recap of previous investigations on this issue




Submission               Slide 18              Chan et al. (Cisco Systems)
March 2008                          doc.: IEEE 802.11-08/0351r0

 Recap of previous investigations on this issue




Submission               Slide 19              Chan et al. (Cisco Systems)

								
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