Cisco Unified Communications Manager (CallManager)

Busy-Out ISDN B-Channels in Cisco CallManager Configuration Example

Document ID: 71647

Updated: Oct 30, 2006



When ISDN PRI users experience intermittent fast busy on outbound calls, you can gracefully busy-out (graceful out-of-service) B-channels for troubleshooting purposes. This document describes how to busy-out B-channels from a Cisco CallManager for Media Gateway Control Protocol (MGCP) controlled T1 or E1 voice ports.



There are no specific requirements for this document.

Components Used

The information in this document is based on Cisco CallManager 3.3, but has been verified on the 4.x and 5.x platforms.

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.


Refer to the Cisco Technical Tips Conventions for more information on document conventions.

Busy-Out B-Channels in Cisco CallManager

In this section, you are presented with the information to configure the features described in this document.

You can gracefully busy-out B-channels from Cisco CallManager for troubleshooting purposes. This can be configured in the Cisco CallManager Administrator web pages. Complete these steps:

  1. Go to the Cisco CallManager Administrator web page.

  2. Choose Service > Service Parameters.

  3. Select any server from the drop-down box, and choose Cisco CallManager from the drop-down box.

  4. Choose Advanced in order to display all of the advanced service parameters.

  5. Under the Cluster Wide Parameters (Device - PRI and MGCP Gateway) heading, enter the value for the parameter called Change B-Channel Maintenance Status 1 (with four other parameters with similar titles for status 2-5).

    This parameter allows the Cisco CallManager to change the individual B-channel maintenance status for PRI interface in real-time for troubleshooting. The input format for this parameter is Device Name = B-Channel Maintenance Status. The device name must exactly match the gateway name on the top of the gateway configuration web page. For example, S0/DS1-0@SDA123456789ABC = 0000 1111 0000 0000 0000 0001 (24 bits for T1. Channel number begins with 1 to 24 from left to right. The last one specifies the D-Channel, which is not affected. In this example, 5th-8th B-Channels are out of service.) Copy and paste the Device Name from CallManager Gateway Configuration Page to this service parameter in order to avoid any manual input mistake. The = is mandatory and unique to distinguish the Device Name and B-Channel Maintenance Status fields. B-Channel Maintenance Status = xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx, where x can be one of these:

    • 0—In service.

    • 1—Graceful out of service. Change channel status after the active call ends if an active call exists on that channel.

    • 2—Forceful out of service. Tear down the active call and change status immediately if an active call exists on that channel.

    The system treats any other value as invalid, and the value does not take effect. Make sure that the total number of x is either 24 for T1 or 32 for E1. Any other invalid length or mismatch (24 for E1) gets treated as an error, and no action gets taken for that device.


    Choose the service parameter to bring up the context-sensitive help in order to find a detailed description of how to configure these advanced service parameters.

  6. Choose PRI Gateway Configuration in the Cisco CallManager and complete these tasks:

    • Uncheck Inhibit restarts at PRI initialization.

    • Check Enable status poll.

    • Restart the gateway in order for the changes to take effect.


Note: For H.323 and SIP gateways, you can also busy-out B-channels for the CAS or CCS(PRI) trunks from the Voice Gateway. Refer to the Troubleshoot section of TDM Switching of Voice and Data Calls on AS5400 Gateways Configuration Example for more information.

Note: You cannot busy-out more than five gateways as documented by Cisco bug ID CSCdx92111 (registered customers only) .

Related Information

Updated: Oct 30, 2006
Document ID: 71647