This document presents two options you can use to resolve a situation when, on Cisco CallManager 3.x, there is a second incoming call on a line and you are unable to transfer any active call on that line. In this scenario the Transfer button is grayed out. This problem occurs due to the limitation on the number of calls per Directory Number (DN). When a new call arrives, both lines are occupied and there is no free line to effect the transfer. This document describes the workaround you can use in order to overcome this problem.
Note: The workarounds this document describes are not required for Cisco CallManager 4.0 because the maximum number of Calls per DN is now database configurable. Refer to How Multiple Calls Per Line Work in Cisco CallManager 4.0 for more information on this.
There are no specific requirements for this document.
The information in this document is tested using Cisco CallManager version 3.3. However, this is applicable to these software and hardware versions:
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.
For more information on document conventions, refer to the Cisco Technical Tips Conventions.
With the current implementation, an IP phone can only handle two calls per line. When you transfer a call, the phone first initiates a new call towards the transfer-to party and then transfers the first call. This means that with every transfer there are two active calls on the line.
When Call Waiting is enabled, an IP phone is able to accept two incoming calls on one line. Because of the requirement mentioned in this document, you are not able to transfer any of those calls. This requires another line instance in order to initiate the additional call towards the transfer-to party.
When there is more than one line on an IP phone, the solution is to disable Call Waiting and configure the first line with Call Forward Busy to the next line.
If there is only one line on the IP phone, you can also disable Call Waiting. However, in this case it is only possible to receive one incoming call. A second incoming call is transferred to the Call Forward Busy extension configured for that line.
Call Waiting can be disabled system wide or on a per line basis. These sections illustrate how to perform both options.
Note: If you disable Call Waiting system wide, all IP phones are affected, unless otherwise configured on specific lines.
Complete these steps in order to disable Call Waiting system wide.
Select Service > Service Parameters for the service Cisco CallManager.
From the Call Waiting Enable Flag drop-down menu select False.
At the top of the Service Parameters Configuration page, click Update.
If you run a cluster environment, repeat steps 1 through 3 for each cluster member.
Complete these steps in order to disable Call Waiting for a specific line.
Go to the Directory Number Configuration of the IP phone. From the Call Waiting drop-down menu select Off.
Refer to Directory Number Configuration Settings for more details.
Click Update and then click OK on the message that appears.
For the changes to take effect, click Reset Devices.
Click OK in order to reset the devices.