[Asterisk-Users] How To conferance

[Ugur GUNCER]

How Can i make conferance  like this


Call came from PRI  
And joining Called Number Conferance Room (211)

While joining progress. 
I want to make Asterisk call sip agent for 2nd conferance person  
When sip agent answer then SIP agent join to room(211)

1st.Conferance Person (PRI)
2nd. Conferance Person (SIP)

If sip agent busy 1st person join conf room 211  directly 

How can i wrote exte. For this plan