does emergency (911) dispatch uses IP ?

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