Content for  TR 23.854  Word version:  11.0.0

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1  Scopep. 6

MPS will enable National Security/Emergency Preparedness (NS/EP) users (herein called Service Users) to make priority calls/sessions using the public networks. This service needs to be ensured also under special conditions such as network congestion. Service Users are the government-authorized personnel, emergency management officials and/or other authorized users. Effective disaster response and management rely on the Service User's ability to communicate during congestion conditions. Service Users are expected to receive priority treatment, in support of mission critical multimedia communications.
The enhancements for MPS evaluated in this document are priority aspects of EPS packet bearer services and priority related interworking between IMS and EPS packet bearer services. These enhancements enable the network to support end-to-end priority treatment for MPS call/session origination/termination, including the Non Access Stratum (NAS) and Access Stratum (AS) signalling establishment procedures at originating/terminating network side as well as resource allocation in the core and radio networks for bearers. Priority treatment will be applicable to IMS based multimedia services, priority EPS bearer services and CS Fallback.
This document clarifies the architectural requirements for MPS, considers the priority service scenarios, and evaluates solution alternatives. Solutions will be proposed and evaluated based on the following three service categories: IMS based multimedia service (voice, video etc), priority EPS bearer services (PS data without IMS interaction) and CS Fallback. Common issues for multiple service categories should be resolved by single solution to limit the amount of overall functionality and to avoid complexity.
The basic eMPS, i.e. priority handling of IMS based multimedia service, EPS bearer services and CS Fallback have completed in Rel 10. In Rel 11, Single Radio Voice Call Continuity (SRVCC) from LTE to UTRAN/GERAN/1xCS will be investigated based on Rel 10 SRVCC specification.
The result of the analysis should be suitable as a basis for normative MPS specification work.
The scope of the MPS part is to further investigate:
  • The signalling and procedures for identifying priority and authorizing the usage of priority service.
  • The required priority attributes used in enabling end-to-end priority marking and priority treatment during establishment, modification and release of an IMS based priority voice/video/data session.
  • The scenarios and capabilities for supporting priority EPS bearer data services.
  • The potential impacts on existing and relevant standard procedures in order to provide preferential treatment for MPS requests in the event of congestion.
  • Inter-working with other IMS and CS networks to provide an end-to-end priority service.

2  Referencesp. 6

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
  • References are either specific (identified by date of publication, edition number, version number, etc.) or non specific.
  • For a specific reference, subsequent revisions do not apply.
  • For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
TR 21.905: "Vocabulary for 3GPP Specifications".
TS 22.153: "Multimedia priority service".
TS 23.401: "General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access".
TS 23.002: "Network architecture".
TS 25.413: "UTRAN Iu interface Radio Access Network Application Part (RANAP) signalling".
TS 23.272: "Circuit Switched (CS) fallback in Evolved Packet System (EPS); Stage 2".
TS 36.331: "Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification".
TS 22.011: "Service accessibility".
3GPP2 A.S0008-C: "Interoperability Specification (IOS) for High Rate Packet Data (HRPD) Radio Access Network Interfaces with Session Control in the Access Network".
3GPP2 A.S0009-C: "Interoperability Specification (IOS) for High Rate Packet Data (HRPD) Radio Access Network Interfaces with Session Control in the Packet Control Function".
TS 24.301: "Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3".
TS 23.228: "IP Multimedia Subsystem (IMS); Stage 2".
TS 24.229: "IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3".
TS 29.228: "IP Multimedia (IM) Subsystem Cx and Dx Interfaces; Signalling flows and message contents".
TS 23.203: "Policy and charging control architecture".
TS 23.216: "Single Radio Voice Call Continuity (SRVCC)".
TS 23.009: "Handover procedures".
TS 48.008: "Mobile Switching Centre - Base Station System(MSC-BSS) interface; Layer 3 specification ".
TS 23.237: "IP Multimedia Subsystem (IMS) Service Continuity; Stage 2".
TS 23.221: "Architectural requirements".

3  Definitions and abbreviationsp. 7

3.1  Definitionsp. 7

For the purposes of the present document, the terms and definitions given in TR 21.905 and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905.
Based on TS 22.153. Multimedia Priority Service allows authorized users to obtain and maintain radio and network resources with priority, also during situations when PLMN congestion is blocking session establishment attempts.
MPS session:
A session (e.g., voice, video, data session) for which priority treatment is applied for allocating and maintaining radio and network resources.
MPS subscription:
A subscription by which priority services are provided, if the network supports MPS. MPS subscription entitles a USIM with special Access Class(es). MPS subscription profile is stored in the operator's network.
MPS-subscribed UE:
A UE having a USIM with MPS subscription.
Service User:
As per TS 22.153.
On-demand MPS:
Priority treatment is explicitly requested by a Service User. Priority treatment is granted by the network and can be revoked by the Service User or network. An example of the On-demand mechanism is the use of specific access code provided by the Service User when activating a session to request priority treatment.
Always-on MPS subscription:
A type of MPS subscription where priority treatment is provided for all PS sessions for the Service User.

3.2  Abbreviationsp. 8

For the purposes of the present document, the abbreviations given in TR 21.905 apply.

4  Priority service scenariosp. 8

4.1  IMS Multimedia Priority Servicep. 8

An example of an IMS-based MPS session is a voice call established using IMS procedures. The MPS voice session described by the following use cases shall be handled in a prioritized way.
  • Mobile origination from an MPS-subscribed UE by including an MPS code/identifier: A Service User originates an IMS-based MPS session by including an MPS code/identifier followed by a destination address (e.g., SIP URI, Tel URI) from an MPS-subscribed UE attached to E-UTRAN. In this scenario, based on the EPS subscription information and operator's policy, priority treatment for the default bearer and the EPS bearer carrying SIP/IMS signalling may be given in the EPS prior to and during IMS-based MPS invocation. Priority treatment in the EPS for signalling and media bearers may be modified/established via PCC based on the session authorization information received from the AF.
  • Mobile origination from any UE by including an MPS input string: A Service User invokes an IMS-based MPS session by including an MPS input string from any UE (MPS subscribed or not) attached to E-UTRAN. Following an IMS-based MPS identification and authorization, priority indication and priority treatment are provided to the session in the EPS via PCC. In this scenario, the UE may also receive priority for signalling and media for collection of additional credentials from the Service User.
  • Mobile termination: A Service User initiates an MPS session to a terminating user (either a Service User or a normal user) in E-UTRAN. The terminating network identifies the priority of the session and applies priority treatment to ensure that the call is delivered with priority.
  • SRVCC of IMS based priority call: When the UE has on-going IMS based priority call and the eNB initiates SRVCC procedure, network resources for voice bearer in the PS, CS and IMS networks of the target system should be reserved in prioritized manner.

4.2  Priority EPS Bearer Servicep. 8

On-demand MPS is activated/deactivated via an AF (e.g., HTTPS server) interaction: The connected Service User interacts with an AF to activate/authorize invocation of priority bearer service. The AF communicates the priority authorization to the PCC infrastructure. Priority is deactivated when the Service User explicitly revokes the priority bearer service via the AF, the AF revokes the priority bearer service or when the PDN connection is released.
For a third-party AF, the invocation/revocation of the On-demand EPS priority treatment may be performed, but outside of the scope of this work.
Always-on MPS receives priority bearer service (e.g. ARP and QCI) for all bearers.

4.3  CS Fallbackp. 9

4.3.1  CS Fallback to GERAN/UTRANp. 9

In the following CS Fallback use case, the CS Fallback related procedures shall be handled in the following way.
  • Mobile-terminating call to a user in E-UTRAN: A Service User initiates a voice call to the terminating user (either a Service User or normal user) in E-UTRAN access and terminating MSC forwards the paging request to the MME. The MME initiates the CS Fallback procedure with priority so that the terminating user can receive the mobile terminating call in the GERAN/UTRAN CS domain.
  • Mobile-originating call by a MPS-subscribed UE in E-UTRAN: A Service User initiates a voice call in E UTRAN using procedure for CS fallback to GERAN/UTRAN with priority indication.

4.3.2  CS Fallback to 1xRTTp. 9

The following two MPS scenarios are supported:
  • Mobile-terminating call to a user in E-UTRAN: A Service User initiates an 1xCS voice call to the terminating user (either a Service User or normal user) in E-UTRAN access and the IWS forwards the paging request to the MME with a priority indication. The MME initiates the CS Fallback procedure with a priority indication in order to transfer the terminating user to the 1x RTT network.
  • Mobile-originating call by a Service User in E-UTRAN: A Service User initiates a voice call in E-UTRAN using procedure for CS fallback to 1xRTT with a priority indication.

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