Tandem switch operation

Last Updated : Oct 03, 2012 |

If the receiving Communication Manager executes a route-to command that routes the call over an ISDN facility before call acceptance, the route-to command is performed on a look-ahead basis in the same manner as a sending Communication Manager. If the call is accepted at a far-end Communication Manager, acceptance is passed to the sending Communication Manager, and call control is passed to the far-end Communication Manager, along with tandeming of the original calling party information and the original DNIS name. If the call is denied, the next step of the tandem switch vector is executed.

The following example shows a tandem switch vector.

Tandem switch vector example

1. goto step 6 if expected-wait in split 30 pri h > 30
2. queue-to split 30 pri h
3. announcement 200
4. wait-time 2 seconds hearing silence
5. stop
6. route-to number 4000 with cov n if unconditionally
7. busy

Step 1 of this vector checks the inflow threshold. If the inflow criteria are acceptable, the vector flow drops to step 2, where the queue-to split command provides acceptance to the sending Communication Manager. Thereafter, steps 3 through 5 provide a typical queuing-wait scheme.

If the inflow criteria are not acceptable, a branch is made to step 6. The route-to command in this step checks another Communication Manager that is enabled with LAI on a look-ahead basis. If this far-end Communication Manager rejects the call, a denial message is relayed back to the tandem Communication Manager, which then drops the LAI call attempt. On the other hand, if the far-end Communication Manager accepts the call, an acceptance message is relayed all the way back to the sending Communication Manager.

No ringback is provided in this tandem Communication Manager vector. This is necessary so that an acceptance message is not returned to the sending Communication Manager. This operation is appropriate for the caller because the sending Communication Manager has already returned an announcement before a LAI attempt is made to the receiving Communication Manager.

Be sure that the sending Communication Manager is not used as a backup location for the tandem Communication Manager or for any of the far-end Communication Manager. If the sending Communication Manager is administered in this manner, all trunk facilities can be tied up by a single call.