Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

Call transfer / number of lines used

When an incoming call from PSTN is transferred to a number back in the PSTN, the gateway (at least the DE-30+) uses two lines. Can this be avoided? Why can't we do it with signaling?

Cisco Employee

Re: Call transfer / number of lines used

This feature is sometimes called anti-tromboning. In order for this to work, the CallManager and the ISDN switch it is connected to need to both be speaking a signaling protocol which supports this feature, where the switch will tandem the call rather than 2 B channels being tied up on the DE-30+.

Currently this is not available in Cisco CallManager. In a later version, the Q.SIG protocol for ISDN will be supported, which does have provisions for providing this functionality, but I do not believe that CallManager will initially support this.

You can contact your Cisco account team so that they can drive the issue with marketing to try and get the functionality added. But I do not know the timeframe that this may require.