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.
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
Technical Tips Conventions for more information on document
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:
Go to the Cisco CallManager Administrator web page.
Choose Service > Service Parameters.
Select any server from the drop-down box, and choose Cisco
CallManager from the drop-down box.
Choose Advanced in order to display all of the
advanced service parameters.
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:
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
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
Choose the service parameter to bring up the context-sensitive help
in order to find a detailed description of how to configure these advanced
Choose PRI Gateway Configuration in the Cisco
CallManager and complete these tasks:
Uncheck Inhibit restarts at PRI
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
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
(registered customers only)