Queues : Only rings available agents


I’ve trouble using queues :
I’m currently using basic ringall strategy for my queues.

I’ve created 2 queues : main_queue which accept all incomming calls and a backup_queue in which calls are transfered after 22sec if they are not answered.

Here is part of the configuration file :

exten = s,n,Queue(main_queue|r|||22)
exten = s,n,Queue(backup_queue,r)

There are regular cell phone among the main_queue members and the problem is that if the incoming call is taken on a cell phone, then all the following incomming calls will be answered by the cell phone’s answering machine. This is not acceptable for me and am looking for a solution which allow to rings available member only.

any idea ?