CAC AP-Load Troubleshooting

Trent Cutler · ‎06-10-2014

Hi All.

I've been crawling over this issue for too long - I need your help. Thanks for whatever time you can give this.

Problem:

Users of the 7925 phones get a "network busy" message and are unable to make phone calls.

Config:

Code: 7.4.121

Supported data rates: 12 Mbps and greater. (6 is disabled)

Mandatory data rate: 24 Mbps

802.11a > Media > VOICE

Admission Control (ACM) is enabled
CAC Method is Load Based
Max RF Bandwidth = 75
Reserved Roaming Bandwidth = 10
Expedited Bandwidth = Checked

CAC Stats:

WMM TSPEC CAC Call Stats 
  Total num of Calls in progress................. 6
  Num of Roam Calls in progress.................. 19617
  Total Num of Calls Admitted.................... 29790
  Total Num of Roam Calls Admitted............... 14145
  Total Num of exp bw requests received.......... 0
  Total Num of exp bw requests Admitted.......... 0
  Total Num of Calls Rejected.................... 14141
  Total Num of Roam Calls Rejected............... 13367
  Num of Calls Rejected due to insufficent bw.... 1
  Num of Calls Rejected due to invalid params.... 4
  Num of Calls Rejected due to PHY rate.......... 13402
  Num of Calls Rejected due to QoS policy........ 734

CAC Stats for AP in Problematic AreaTemporary Solution:

Call Admission Control (CAC) Stats
  Voice Bandwidth in use(% of config bw)......... 2
  Voice Roam Bandwidth in use(% of config bw).... 0
    Total channel MT free........................ 26686
    Total voice MT free.......................... 23811
    Na Direct.................................... 24
    Na Roam...................................... 27
  Video Bandwidth in use(% of config bw)......... 0
  Video Roam Bandwidth in use(% of config bw).... 0
  Total BW in use for Voice(%)................... 2
  Total BW in use for SIP Preferred call(%)...... 0

WMM TSPEC CAC Call Stats 
  Total num of voice calls in progress........... 1
  Num of roaming voice calls in progress......... 416
  Total Num of voice calls since AP joined....... 4099

  Total Num of roaming calls since AP joined..... 1954
  Total Num of exp bw requests received.......... 0
  Total Num of exp bw requests admitted.......... 0
  Num of voice calls rejected since AP joined.... 1361
  Num of roam calls rejected since AP joined..... 1357
  Num of calls rejected due to insufficent bw.... 0
  Num of calls rejected due to invalid params.... 1
  Num of calls rejected due to PHY rate.......... 1360
  Num of calls rejected due to QoS policy........ 0

If I am reading this correctly it rejects about 1/5 of all calls attempted. Seems unacceptable, right?

Channel Utilization of AP in Problem Area

(Cisco Controller) >show 802.11a cu-metrics 125


AP Interface Mac:           6c:9c:ed
Measurement Duration:       90sec

 Timestamp               Tue Jun 10 14:56:16 2014

   Channel Utilization stats
   ================
     Picc (50th Percentile)...................... 0
     Pib (50th Percentile)....................... 1
     Picc (90th Percentile)...................... 0
     Pib (90th Percentile)....................... 2

 Timestamp               Tue Jun 10 15:09:56 2014

   Channel Utilization stats
   ================
     Picc (50th Percentile)...................... 0
     Pib (50th Percentile)....................... 1
     Picc (90th Percentile)...................... 0

--More-- or (q)uit
     Pib (90th Percentile)....................... 1

 Timestamp               Tue Jun 10 15:32:44 2014

   Channel Utilization stats
   ================
     Picc (50th Percentile)...................... 0
     Pib (50th Percentile)....................... 1
     Picc (90th Percentile)...................... 0
     Pib (90th Percentile)....................... 1

 Timestamp               Tue Jun 10 14:48:40 2014

   Channel Utilization stats
   ================
     Picc (50th Percentile)...................... 0
     Pib (50th Percentile)....................... 0
     Picc (90th Percentile)...................... 0
     Pib (90th Percentile)....................... 1

 Timestamp               Tue Jun 10 14:51:42 2014

   Channel Utilization stats

--More-- or (q)uit
   ================
     Picc (50th Percentile)...................... 0
     Pib (50th Percentile)....................... 1
     Picc (90th Percentile)...................... 0
     Pib (90th Percentile)....................... 1

 Timestamp               Tue Jun 10 14:53:13 2014

   Channel Utilization stats
   ================
     Picc (50th Percentile)...................... 0
     Pib (50th Percentile)....................... 0
     Picc (90th Percentile)...................... 0
     Pib (90th Percentile)....................... 1

 Timestamp               Tue Jun 10 14:54:44 2014

   Channel Utilization stats
   ================
     Picc (50th Percentile)...................... 0
     Pib (50th Percentile)....................... 1
     Picc (90th Percentile)...................... 0
     Pib (90th Percentile)....................... 1

Temporary Solution:

Disable CAC. This will stop the network busy messages and allow the phones to make calls with some degradation.

Anyway, thanks again for looking through this.

mohanak · ‎06-11-2014

Verify all these process

When using a controller, add the following QoS policies:

•Platinum (voice)—Apply this policy to your voice WLAN SSID/VLAN for both incoming and outgoing traffic

http://www.cisco.com/en/US/docs/voice_ip_comm/cuipph/7925g/7_0/english/administration/guide

/7925cklt.html

Using RF Profiles on WiSM2 causes network busy on 7925 phones

CSCuc07175

Symptom:
While using RF Profile that matches existing RF network the 7925 phone will display network busy.

Conditions:
While using RF Profile that matches existing RF network the 7925 phone will display network busy.

Workaround:
Disable ACM or use global RF settings.

Trent Cutler · ‎06-11-2014

Thank you for your response. Platinum voice is being used. These are 5508 controllers, so should I still be using global RF settings?

I am now suspicious that the problem exists between APs with an RF profile and APs using global RF settings. Looks like the difference is that the same SSID exists, with different minimum data rates.

Would that cause a network busy?

Leo Laohoo · ‎06-11-2014

Supported data rates: 12 Mbps and greater.

HTML into the phone and confirm 12 Mbps is supported.