802.11N MCS related issue of AIR-CT2504-K9 & AIR-LAP1142N-T-K9

Falcon Chung · ‎08-27-2013

The story is:

After I set MCS parameter to 8 as below:

then, the data rate of STA shows Tx=5.5, Rx=39.0, as you can see below:

Isn't the data rate supposed to be 14 Mbps@MCS 8(20MHz, short GI)?

How's the values 5.5 / 39 would happen?

Would anyone could explain it please?

Thank you very much.

Erwin Salazar · ‎08-27-2013

Hi Falcon,

Are you certain this client was connected at MCS 8? Issue a 'show client detail ' from the CLI of the controller.

Cheers,
Erwin

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Falcon Chung · ‎08-27-2013

Hi Erwin:

Thanks for your kindly reply.

After executing the command, i found that even i set MCS to 8, the Current Rate is still dynamic changing. Every time i execute the command, it usually reports another different current rate to me. The data rate is unable to fix at MCS 8.

Is this behavior correct? Because i have checked the MCS8 checking box ONLY. (refer to previous snapshot)

As i know some access point will fix the data rate if user sets a fixed MCS parameter. I think it's more reasonable. Isn't it?

Thank you.

=================================================================
(Cisco Controller) >show client detail 00:1d:73:a2:5a:9b
Client MAC Address............................... 00:1d:73:a2:5a:9b
Client Username ................................. N/A
AP MAC Address................................... 34:a8:4e:5c:a8:a0
AP Name.......................................... APfc99.4744.2401
Client State..................................... Associated
Client NAC OOB State............................. Access
Wireless LAN Id.................................. 1
802.11u.......................................... Not Supported
BSSID............................................ 34:a8:4e:5c:a8:a0
Connected For ................................... 571 secs
Channel.......................................... 1
IP Address....................................... 192.168.5.195
IPv6 Address..................................... fe80::8485:756e:50fb:1fc4
Association Id................................... 1
Authentication Algorithm......................... Open System
Reason Code...................................... 1
Status Code...................................... 0
Session Timeout.................................. 1800
Client CCX version............................... 5
Client E2E version............................... No E2E support
Diagnostics Capability........................... Not Supported
S69 Capability................................... Not Supported

--More-- or (q)uit
QoS Level........................................ Silver
802.1P Priority Tag.............................. disabled
CTS Security Group Tag........................... Not Applicable
KTS CAC Capability............................... No
WMM Support...................................... Enabled
Power Save....................................... OFF
Current Rate..................................... m8
Supported Rates.................................. 1.0,2.0,5.5,11.0,6.0,9.0,
     ............................................. 12.0,18.0,24.0,36.0,48.0,
     ............................................. 54.0
Mobility State................................... Local
Mobility Move Count.............................. 0
Security Policy Completed........................ Yes
Policy Manager State............................. RUN
Policy Manager Rule Created...................... Yes
Audit Session ID................................. none
IPv4 ACL Name.................................... none
IPv4 ACL Applied Status.......................... Unavailable
IPv6 ACL Name.................................... none
IPv6 ACL Applied Status.......................... Unavailable
Policy Type...................................... WPA2
Authentication Key Management.................... PSK
Encryption Cipher................................ CCMP (AES)

--More-- or (q)uit
Management Frame Protection...................... No
EAP Type......................................... Unknown
Interface........................................ management
VLAN............................................. 0
Quarantine VLAN.................................. 0
Access VLAN...................................... 0
Client Capabilities:
       CF Pollable................................ Not implemented
       CF Poll Request............................ Not implemented
       Short Preamble............................. Implemented
       PBCC....................................... Not implemented
       Channel Agility............................ Not implemented
       Listen Interval............................ 3
       Fast BSS Transition........................ Not implemented
Client Wifi Direct Capabilities:
       WFD capable................................ No
       Manged WFD capable......................... No
       Cross Connection Capable................... No
       Support Concurrent Operation............... No
Fast BSS Transition Details:
Client Statistics:
       Number of Bytes Received................... 188075
       Number of Bytes Sent....................... 120678

--More-- or (q)uit
       Number of Packets Received................. 1208
       Number of Packets Sent..................... 1084
       Number of Interim-Update Sent.............. 2
       Number of EAP Id Request Msg Timeouts...... 0
       Number of EAP Request Msg Timeouts......... 0
       Number of EAP Key Msg Timeouts............. 0
       Number of Data Retries..................... 941
       Number of RTS Retries...................... 0
       Number of Duplicate Received Packets....... 0
       Number of Decrypt Failed Packets........... 0
       Number of Mic Failured Packets............. 0
       Number of Mic Missing Packets.............. 0
       Number of RA Packets Dropped............... 0
       Number of Policy Errors.................... 0
       Radio Signal Strength Indicator............ -38 dBm
       Signal to Noise Ratio...................... 33 dB
Nearby AP Statistics:
       APfc99.4744.2401(slot 0)
         antenna0: 559 secs ago................... -47 dBm
         antenna1: 559 secs ago................... -39 dBm

(Cisco Controller) >
=================================================================