On 01/28/2011 02:39 PM, Ben Greear wrote:
When testing with 60 stations, 30 against a netgear running HT40 and 30 against a cheap cisco AP, using HT20, I notice that the stations on the netgear often choose NO_HT instead of HT40 for their channel type. The root cause appears to be that the hti->control_chan is 15 in the ieee80211_enable_ht method. Everything *should* be running on channel 11. Is this just a bug with the AP, or could this be a local issue?
I sniffed on a separate machine (using ath9k NIC), and it agrees
that the beacon's control_channel is 14 (I have since set the AP to channel
10 instead of 11, but the control_channel remains 4 higher than expected.)
I'm attaching the pkt in pcap format as well.
(From wireshark):
Vendor Specific: 00:90:4c: HT Additional Capabilities (802.11n D1.00)
Tag Number: 221 (Vendor Specific)
Tag length: 26
Vendor: 00:90:4c
Tag interpretation: 802.11n (Pre) OUI
Tag interpretation: HT additional information (802.11n D1.00)
Tag interpretation: Control Channel 14
HT Additional Capabilities: 0x000F
.... .... .... ..11 = Extension Channel Offset: Extension Channel below control channel (0x0003)
.... .... .... .1.. = Recommended Tx Channel Width: Any channel width enabled
.... .... .... 1... = Reduced Interframe Spacing (RIFS) Mode: Use of RIFS permitted
.... .... ...0 .... = Controlled Access Only: PSMP only
.... .... 000. .... = Service Interval Granularity: 5ms (0x0000)
HT Additional Capabilities: 0x0008
.... .... .... ..00 = Operating Mode: Pure HT, no protection (0x0000)
.... .... .... .0.. = Non Greenfield (GF) devices Present: One or More HT devices are not GF capable
HT Additional Capabilities: 0x0000
.... .... .000 0000 = Basic STB Modulation and Coding Scheme (MCS): 0x0000
.... .... 0... .... = Dual Clear To Send (CTS) Protection: Regular use of RTS/CTS
.... ...0 .... .... = Secondary Beacon: Primary Beacon
.... ..0. .... .... = L-SIG TXOP Protection Support: Not full support
.... .0.. .... .... = Phased Coexistence Operation (PCO) Active: PCO is not activated in the BSS
.... 0... .... .... = Phased Coexistence Operation (PCO) Phase: Switch to 40MHz phase/keep 40MHz
Rx Supported Modulation and Coding Scheme Set (VS): MCS Set
Tag interpretation: Rx Modulation and Coding Scheme (One bit per modulation)
.... .... .... .... .... .... 0000 0000 = Rx Bitmask Bits 0-7: 0x00000000
.... .... .... .... 0000 0000 .... .... = Rx Bitmask Bits 8-15: 0x00000000
.... .... 0000 0000 .... .... .... .... = Rx Bitmask Bits 16-23: 0x00000000
0000 0000 .... .... .... .... .... .... = Rx Bitmask Bits 24-31: 0x00000000
.... .... .... .... .... .... .... ...0 = Rx Bitmask Bit 32: 0x00000000
.... .... .... .... .... .... .000 000. = Rx Bitmask Bits 33-38: 0x00000000
.... .... ...0 0000 0000 0000 0... .... = Rx Bitmask Bits 39-52: 0x00000000
...0 0000 0000 0000 0000 0000 000. .... = Rx Bitmask Bits 53-76: 0x00000000
Highest Supported Data Rate: 0x0000
.... .... .... ...0 = Tx Supported MCS Set: Not Defined
.... .... .... ..0. = Tx and Rx MCS Set: Equal
.... .... .... 00.. = Tx Maximum Number of Spatial Streams Supported: 1 spatial stream (0x0000)
.... .... ...0 .... = Unequal Modulation: Not supported
HT Information (802.11n D1.10)
Tag Number: 61 (HT Information (802.11n D1.10))
Tag length: 22
Primary Channel: 14
HT Information Subset (1 of 3): 0x0F
.... ..11 = Secondary channel offset: Secondary channel is below the primary channel (0x03)
.... .1.. = Supported channel width: Channel of any width supported
.... 1... = Reduced Interframe Spacing (RIFS): Permitted
...0 .... = Power Save Multi-Poll (PSMP) stations only: Association requests are accepted regardless of PSMP capability
000. .... = Shortest service interval: 5 ms (0x00)
HT Information Subset (2 of 3): 0x0008
.... .... .... ..00 = Operating mode of BSS: All STAs are - 20/40 MHz HT or in a 20/40 MHz BSS or are 20 MHz HT in a 20 MHz BSS (0x0000)
.... .... .... .0.. = Non-greenfield STAs present: All associated STAs are greenfield capable
.... .... .... 1... = Transmit burst limit: 2.4 GHz - 6.16 ms | All other bands - 3.08 ms
.... .... ...0 .... = OBSS non-HT STAs present: Use of protection for non-HT STAs by overlapping BSSs is not needed
0000 0000 000. .... = Reserved: 0x0000
HT Information Subset (3 of 3): 0x0000
.... .... ..00 0000 = Reserved: 0x0000
.... .... .0.. .... = Dual beacon: No second beacon is transmitted
.... .... 0... .... = Dual Clear To Send (CTS) protection: Not required
.... ...0 .... .... = Beacon ID: Primary beacon
.... ..0. .... .... = L-SIG TXOP Protection Full Support: One or more HT STAs in the BSS do not support L-SIG TXOP protection
.... .0.. .... .... = Phased Coexistence Operation (PCO): Inactive
.... 0... .... .... = Phased Coexistence Operation (PCO) Phase: Switch to or continue 20 MHz phase
0000 .... .... .... = Reserved: 0x0000
Rx Supported Modulation and Coding Scheme Set: Basic MCS Set
Tag interpretation: Rx Modulation and Coding Scheme (One bit per modulation)
.... .... .... .... .... .... 0000 0000 = Rx Bitmask Bits 0-7: 0x00000000
.... .... .... .... 0000 0000 .... .... = Rx Bitmask Bits 8-15: 0x00000000
.... .... 0000 0000 .... .... .... .... = Rx Bitmask Bits 16-23: 0x00000000
0000 0000 .... .... .... .... .... .... = Rx Bitmask Bits 24-31: 0x00000000
.... .... .... .... .... .... .... ...0 = Rx Bitmask Bit 32: 0x00000000
.... .... .... .... .... .... .000 000. = Rx Bitmask Bits 33-38: 0x00000000
.... .... ...0 0000 0000 0000 0... .... = Rx Bitmask Bits 39-52: 0x00000000
...0 0000 0000 0000 0000 0000 000. .... = Rx Bitmask Bits 53-76: 0x00000000
Highest Supported Data Rate: 0x0000
.... .... .... ...0 = Tx Supported MCS Set: Not Defined
.... .... .... ..0. = Tx and Rx MCS Set: Equal
.... .... .... 00.. = Tx Maximum Number of Spatial Streams Supported: 1 spatial stream (0x0000)
.... .... ...0 .... = Unequal Modulation: Not supported
Thanks, Ben
-- Ben Greear <greearb@xxxxxxxxxxxxxxx> Candela Technologies Inc http://www.candelatech.com
Attachment:
wifi-n-bad-ctrl-channel.pcap
Description: Binary data
