Section: 4.3.18 Multimedia Priority Service 4.3.18.1 General
Content: Multimedia Priority Service (MPS) allows certain subscribers (i.e. Service Users as per TS 22.153[ Multimedia priority service ]  [68]) priority access to system resources in situations such as during congestion, creating the ability to deliver or complete sessions of a high priority nature. Service Users are government-authorized personnel, emergency management officials and/or other authorized users. MPS supports priority sessions on an "end-to-end" priority basis. MPS is based on the ability to invoke, modify, maintain and release sessions with priority, and deliver the priority media packets under network congestion conditions. MPS is supported in a roaming environment when roaming agreements are in place and where regulatory requirements apply. NOTE 1: If a session terminates on a server in the Internet (e.g. web-based service), then the remote end and the Internet transport are out of scope for this specification. MPS is supported for Service Users using UEs connecting via 3GPP access. MPS is also supported for Service Users using UEs that support connecting via Trusted or Untrusted non-3GPP access via WLAN as specified in TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [2] for MPS. ePDG selection is according to clause 4.5.4 in TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [2]. A Service User obtains priority access to the Radio Access Network by using the Access Class Barring mechanism according to TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [37] and TS 22.011[ Service accessibility ]  [67]. This mechanism provides preferential access to UEs based on its assigned Access Class. If a Service User belongs to one of the special access-classes as defined in TS 22.011[ Service accessibility ]  [67], the UE has preferential access to the network compared to ordinary users in periods of congestion. MPS subscription allows users to receive priority services, if the network supports MPS. The same MPS subscription applies to access via 3GPP access and non-3GPP access via WLAN. MPS subscription entitles a USIM with special Access Class(es). MPS subscription includes indication for support of Priority EPS Bearer Service, IMS priority service and CS Fallback priority service support for the end user. Priority level regarding Priority EPS Bearer Service and IMS are also part of the MPS subscription information. The usage of priority level is defined in TS 23.203[ Policy and charging control architecture ]  [6] and TS 23.228[ IP Multimedia Subsystem (IMS); Stage 2 ]  [52]. NOTE 2: The MPS subscription on the USIM is also used for 3GPP procedures with priority treatment over WLAN for UEs that support MPS over Trusted and Untrusted non-3GPP access via WLAN feature. NOTE 3: The above statements for the Priority EPS Bearer Service are also applicable for the MPS for Data Transport Service. An MPS Service User is treated as an On Demand MPS subscriber or not, based on regional/national regulatory requirements. On Demand service is based on Service User invocation/revocation explicitly and applied to the PDN connections for an APN. When not On Demand, MPS service does not require invocation, and provides priority treatment for all EPS bearers for a given Service User after attachment to the EPS network. NOTE 4: According to regional/national regulatory requirements and operator policy, On-Demand MPS Service Users can be assigned the highest priority. Since the Service User has an access class within the range for priority services, the Establishment Cause in RRC connection request is set to highPriorityAccess. When the eNodeB receives mobile initiated signalling with establishment cause set to highPriorityAccess, the eNodeB handles the RRC connection request with priority. When the MME receives and verifies mobile initiated signalling with establishment cause set to highPriorityAccess, the MME establishes the S1 bearer with priority. The terminating network identifies the priority of the MPS session and applies priority treatment, including paging with priority, to ensure that the MPS session can be established with priority to the terminating user (either a Service User or normal user). Priority treatment for MPS includes priority message handling, including priority treatment during authentication, security, and location management procedures. Priority treatment for MPS session requires appropriate ARP and QCI (where necessary for non-GBR bearers) setting for bearers according to the operator's policy. When an MPS session is requested by a Service User, the following bearer management principles apply in the network: - EPS bearers (including default bearer) employed in an MPS session shall be assigned ARP value settings appropriate for the priority level of the Service User. - Setting ARP pre-emption capability and vulnerability for MPS bearers, subject to operator policies and depending on national/regional regulatory requirements. - Pre-emption of non-Service Users over Service Users during network congestion situation, subject to operator policy and national/regional regulations. Priority treatment is applicable to IMS based multimedia services, priority EPS bearer services (PS data without IMS interaction) and CS Fallback. For Multimedia Priority services any EPC functions, procedures and capabilities are provided according to this clause's specification except when specified differently in the following clauses.