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Call Admission Control (CAC) and channel utilization (CU) displayed on 792x series wireless handsets

 

 

Introduction

In this document Cisco TAC engineer "Michael Combs" has explained about Issue faced with CAC and channel utilization (CU) displayed on 792x series wireless handsets

 

Problem Subcategory

Wireless Services Module (WS-SVC-WISM)

 

Problem Details

Is the channel utilization (CU) on the phone coming from the AP or is the phone itself deriving this number? When we see "network busy" on the phone, Does the phone CU derive this or is this part of CAC ?

 

Resolution

The channel utilization (CU) information displayed on the 7925G in the site survey/neighbor list is a metric derived from the AP. The handset is extracting this information from the appropriate IE in the beacons and probe responses for the BSSID in question. Specifically in the 'QBSS Load' IE section for each of these respective 802.11 management frames.

 

When correlating this to call admission control (CAC), a high CU, low medium time (MT) availability, TSPEC/EDCA mismatch, and a list of other potential TSPEC/CCX related issues can all lead to a 'Network Busy' error and subsequent TSPEC rejection for the handset.

 

The best means of isolating the root cause of a CAC/TSPEC rejection is to gather an over-the-air (OTA) packet capture of this issue, while also running the following debug commands on the WLC in question:

 

- debug client <MAC_addr>

- debug cac all enable

 

Related Information

 

Debug Client

 

The command debug client <MACADDRESS> is a macro that enables eight debug commands, plus a filter on the MAC address provided, so only messages that contain the specified MAC address are shown. The eight debug commands show the most important details on client association and authentication. The filter helps with situations where there are multiple wireless clients. Situations such as when too much output is generated or the controller is overloaded when debugging is enabled without the filter.

The information collected covers important details about client association and authentication (with two exceptions mentioned later in this document).

The commands that are enabled are shown in this output:

(Cisco Controller) >show debug MAC address ................................ 00:00:00:00:00:00 
Debug Flags Enabled:  
dhcp packet enabled.  
dot11 mobile enabled.  
dot11 state enabled.  
dot1x events enabled.  
dot1x states enabled.  
pem events enabled.  
pem state enabled.

 

These commands cover address negotiation, 802.11 client state machine, 802.1x authentication, Policy Enforcement Module (PEM), and address negotiation (DHCP).

 

Debug Client Variations

For most scenarios, the debug client <MACAddress> command is enough to get the information needed. However, here are two important situations where additional debugging is needed:

 

Mobility

In this situation, mobility debugs need to be enabled after the debug client <MACAddress> command has been introduced in order to gain additional information on the mobility protocol interaction between controllers.

 

Note: Details on this output will be covered in future documents.

In order to enable mobility debugs, use the debug client <MACAddress>, and then use the debug mobility handoff enable command:

 

(Cisco Controller) >debug client 00:00:00:00:00:00 
(Cisco Controller) >debug mobility handoff enable 

(Cisco Controller) >show debugMAC address ................................ 
00:00:00:00:00:00
Debug Flags Enabled:  
dhcp packet enabled.  
dot11 mobile enabled.  
dot11 state enabled  
dot1x events enabled.  
dot1x states enabled.  
mobility handoff enabled.  
pem events enabled.  
pem state enabled.

 

EAP Authentication Troubleshooting

In order to troubleshoot the interaction between the WLC and the authentication server (external RADIUS or internal EAP server), use the command debug AAA all enable, which shows the required details. This command should be used after the debug client <MACAddress> command and can be combined with other debug commands as needed (for example, handoff).

(Cisco Controller) >debug client 00:00:00:00:00:00(Cisco Controller) 
>debug aaa all enable (Cisco Controller) 
>show debugMAC address ................................ 
00:00:00:00:00:00
Debug Flags Enabled:  
aaa detail enabled.  
aaa events enabled.  
aaa packet enabled.  
aaa packet enabled.  
aaa ldap enabled.  
aaa local-auth db enabled.  
aaa local-auth eap framework errors enabled.  
aaa local-auth eap framework events enabled.  
aaa local-auth eap framework packets enabled.  
aaa local-auth eap framework state machine enabled.  
aaa local-auth eap method errors enabled.  
aaa local-auth eap method events enabled.  
aaa local-auth eap method packets enabled.  
aaa local-auth eap method state machine enabled.  
aaa local-auth shim enabled.  aaa tacacs enabled.  
dhcp packet enabled.  dot11 mobile enabled.  
dot11 state enabled  dot1x events enabled  
dot1x states enabled.  mobility handoff enabled.  
pem events enabled.  pem state enabled.

 

More Information

Understanding Debug Client on Wireless LAN Controllers (WLCs)

Troubleshooting Call Admissions Control

Version history
Revision #:
2 of 2
Last update:
‎08-29-2017 07:31 AM
Updated by:
 
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