does emergency (911) dispatch uses IP ?

["Mankamana Mishra \(mankamis\) via NANOG" <nanog () nanog org>]

Guys,
While reading CL network down impacting 911 services, was trying to get more information about how does this network 
looks like. From end user to center, I guess VOIP is used. Wondering what is the communication method from  Emergency 
service center to end units (Police, Fire or any other services). Do they also use IP ? or its Still Radio only ?  if 
it is IP, do they use Unicast or multicast or broadcast ?

Tried googling, but did not get much information. Any insight would be appreciated.

Thanks
Mankamana