Dialplan improvement

Following Dialplan allows me to assign call to a extesion that is not busy.

(I have put call-limit=1 for each extenstion in sip.conf)

In following dialplan what imporvements I can do? Because If I want to add more extensions then I have to modify follwing list

exten => 4000,1,Dial(SIP/100,20)
exten => 4000,n,Dial(SIP/101,20)
exten => 4000,n,Dial(SIP/102,20)
exten => 4000,n,Dial(SIP/103,20)
exten => 4000,n,Goto(4000,1)

How I can use s?

you can do multiple things asterisk is very powerfull

you can also ring multiple extensions at the same time

exten => 4000,n,Dial(SIP/101&SIP/102&SIP/103,20)

also you can make a queue in queues.con that rings each extensions after another

take a look at

here you can find what you need