o-mobile networks, mobile-to-fixed networks, to fixed- to-mobile networks. MPS provides broadband IP-based multimedia services (IMS-based and non-IMS-based) over wireless networks in support of voice, video, and data services. Network support for MPS will require end-to-end priority treatment in call/session origination/termination including the non-access stratum (NAS) and access stratum (AS) signaling establishment procedures at originating/terminating network side as well as resource allocation in the core and radio networks for bearers. The MPS will also require end-to-end prior- ity treatment in case of roaming if supported by the visiting network and if the roaming user is authorized to receive priority service. Ixxii Introduction and Background Communication service availability Application A and Communication Application B and Communication communication Mobile network communication service interface A node A node B service interface B protocol protocol Reliability Figure 14 Illustration of the relationship between communication service availability and reliability [21]. common QoS characteristics as applicable for normal public voice communications, yet they may have different priority requirements. The 5G network supports mechanisms that allow decoupling of the priority of a particular communication from the associated QoS characteristics such as latency and reliability to allow flexibility and configurability to support different priority services in operators' networks while adhering to their net- work policies and the corresponding national/regional regulations. The network needs to support flexible means to make priority decisions based on the state of the network (e.g., during disaster events and network congestion) recognizing that the service priori- ties may change during a crisis. The priority of any service may be different for each user depending on the operational requirements and regional/national regulations. The 5G systems provide flexible means to prioritize and enforce prioritization am