Emergency Attach is used by UEs which needs to perform emergency service but cannot connect to the network normally. These UEs are in limited service state, because generally these UEs are in a location which has restricted service. During an emergency attach, only UE having authorisation for public safety services are allowed to attach. These emergency devices or mission critical handsets must have an IMSI. Even if authentication fails, these devices are granted access and the unauthenticated IMSIs are retained in the network.