The present document specifies the stage 2 description of the enhanced Multi-Level Precedence and Pre-emption Service (eMLPP) which provides different call priorities in combination with fast call set-up and pre-emption for different applications according to TS 22.067.
For the purposes of the present document, the terms and definitions given in TS 22.067 and the following apply:
the termination of a call of a low priority user such that resources can be made available for a precedence call of higher priority. Resource pre-emption could be initiation resource pre-emption or handover resource pre-emption
termination of a call to a particular user when a higher priority call is directed towards that specific user. Called party pre-emption is decided by the Mobile Station. In case of point-to-point calls, this shall be performed by Call Waiting with automatic acceptance of the waiting call by the Mobile Station
compatible Mobile Station:
mobile stations which support eMLPP and therefore have precedence and pre-emption capabilities
non-compatible Mobile Station:
mobile stations which do not support eMLPP
subscriber Identity Module. This specification makes no distinction between SIM and USIM.
This specification uses the term handover for GSM and the same term meaning relocation in UMTS.
The enhanced Multi-Level Precedence and Pre-emption service (eMLPP) provides different levels of precedence for call set-up and for call continuity in case of handover.
There are seven priority levels which are defined in TS 22.067. The highest level (A) is reserved for network internal use. The second highest level (B) may be used for network internal use or, optionally, depending on regional requirements, for subscription. These two levels (A and B) may only be used locally, i.e. in the domain of one MSC. The other five priority levels are offered for subscription and may be applied globally, e.g. on inter switch trunks, if supported by all related network elements, and also for interworking with ISDN networks providing the MLPP service.
The seven priority levels are defined as follows:
(highest, for network internal use)
(for network internal use or, optionally, for subscription)
(lowest, for subscription).
Levels A and B shall be mapped to level 0 for priority treatment outside of the MSC area in which they are applied.
As a network specific configuration, the ability to pre-empt other calls of lower priority and the application of fast call set-up procedures can be assigned to each priority level. An example for an eMLPP configuration is given in TS 22.067.
Considering aspects of priority handling, the following issues can be considered for each call:
contention during the initial random access (no specific definitions apply for eMLPP. Delays due to access collision have to be managed by a corresponding planning of the network resources);
in GSM, contention in gaining radio resources during the call set-up phase and during handover (this item relates to the assignment of SDCCH and TCH for which queuing and pre-emption mechanisms are applied for eMLPP);
in UMTS, contention in gaining radio resources during the call set-up phase and during relocation (this item relates to the assignment of DCCH and DTCH for which queuing and pre-emption mechanisms are applied for eMLPP);
A pre-emption might already be performed as a network option on the basis of the establishment cause if a network specific eMLPP configuration assigns a certain priority level to a particular establishment cause.
contention in gaining terrestrial resources inside the GSM or UMTS network (this item relates to the assignment of terrestrial channels between the GSM or UMTS network nodes. Priority actions shall be performed on basis of the MLPP service implementations. The eMLPP priority levels A and B shall be mapped to the MLPP priority level 0. No further specific definitions apply for eMLPP);
contention in gaining terrestrial resources in external networks (this item relates to interworking with external networks which shall be performed on basis of the MLPP service if provided in the related external networks.);
application of different call set-up procedures in relation to the priority levels and the network specific configuration (three classes of set-up performance are defined in TS 22.067, one very fast class for VBS or VGCS emergency call services, one class for fast but normal set-up times and one class allowing some delay in the set-up. The application of the corresponding procedures shall be decided by the network on the basis of the requested priority level);
automatic answering of calls if the incoming call exceeds a defined priority level (if the MS is in idle mode), or called party pre-emption (if the called subscriber is engaged in communication of a lower priority);
the means by which the called user is informed of priority issues and is able to make appropriate decisions if no called party pre-emption applies;
the accommodation of non-compatible Mobile Stations.
The definitions in the present specification focus on the issues under item b), e), f), g) and h). Items c) and d) are related to the MLPP service implementation for the signalling system No. 7 according to ITU-T Recommendations Q.85 and Q.735.
For a call establishment, a subscriber shall be able to select any one of the priority levels he has subscribed to.
Priorities shall be treated in the network as defined in TS 22.067. Priority treatment is different for point-to-point calls and voice broadcast calls or voice group calls, respectively:
mobile originated point-to-point call:
The priority level depends on the calling subscriber. If the user has no eMLPP subscription, the call shall have a default priority level defined in the network. If the user has an eMLPP subscription, the call shall have the priority level selected by the user at set-up or the priority level predefined by the subscriber as default priority level by registration.
mobile terminated point-to-point calls:
The priority level depends on the calling party. For this, interworking with the ISDN MLPP service is required. If the call is not an MLPP call, i.e. no priority level is defined, the call shall be treated in the mobile network with a default priority level. If the call is an MLPP call, the call shall be treated with the priority level provided by the interfacing network.
mobile to mobile point-to-point calls:
The priority shall be treated for the calling subscriber as for mobile originated calls and for the called subscriber as for mobile terminated calls. However, an interworking with MLPP is not required if both the calling subscriber and the called subscriber are located in the same MSC area.
Voice Broadcast Calls (VBS) and Voice Group Calls (VGCS):
The link on the voice broadcast call channel or voice group call channel shall have the priority level as defined in the corresponding registration for the related voice broadcast call or voice group call in the GCR. At the early stage of a voice broadcast call or voice group call establishment, before the GCR request is made and the voice broadcast call channel or voice group call channels are assigned, the procedure shall be the same as for point-to-point calls. If the GCR response includes a priority level it shall be applied to the dedicated link of the calling mobile station as well.
Queuing and resource pre-emption shall then be applied as appropriate according to the network service configuration. In addition, automatic answering or called party pre-emption shall be applied as appropriated according to the Mobile Station's internal service configuration.
The MSC shall maintain a record of the priority level of each call in progress in its area such that it can arbitrate over resources in a defined manner.
The priority level can be included in the CM_SERVICE_REQUEST message in the case that a user establishing a point-to-point call is using a compatible Mobile Station (see clause 6).
If the subscriber has not selected a priority level for that call or uses a non compatible Mobile Station (see clause 6), the priority level shall be assigned according to the respective VLR data.
The priority level of a call shall be determined by the MSC. Accordingly, the MSC shall request channel assignment with an indication of the priority level and the pre-emption capability of that call. For this the MSC shall use the priority message element as defined in TS 48.008. Mapping of the priority information in this message element on the network specific eMLPP configuration shall be performed in the MSC. Queuing and resource pre-emption shall be performed accordingly if necessary.
In GSM, in addition to the priority signalling, the requirement for a direct assignment of a TCH shall be included in the establishment cause of the CHAN_REQ message in order to support a fast call set-up procedure in the BSC at the earliest possible stage of the call establishment for high priority calls if applicable.
In UMTS, in addition to the priority signalling, the RRC CONNECTION REQUEST message shall be included the establishment cause.
Automatic answering or, if necessary, called-party pre-emption has to be performed by the Mobile Station as defined in the following:
If the user is in idle mode, the Mobile Station shall automatically connect to an incoming call of a sufficient priority level. The priority level shall be included in the paging message and in the set-up message. If the user is in dedicated mode and has a subscription to Call Waiting, a Call Waiting indication including the priority level of the call shall be given to the Mobile Station which automatically accepts the waiting call.
There is no called party pre-emption for point-to-point calls without Call Waiting.
voice group calls and voice broadcast calls:
Notifications for other voice group calls, voice broadcast calls or information on paging for point-to-point calls shall be given to the Mobile Stations involved in on-going voice group calls or voice broadcast calls as defined in TS 43.068 and TS 43.069, respectively. The notifications include the related priority level of the call. In case of a notified call with higher priority where called-party pre-emption applies, the Mobile Station shall automatically leave the on-going voice group call or voice broadcast call and react according to the type of the notified call type.
For both cases, the priority level applied shall be included, either in the paging message or Call Waiting indication, or in the notification message, in order to enable the Mobile Station to decide on an automatic reaction (automatic answering or called-party pre-emption) or to indicate the incoming, non pre-empting call to the user.
The priority information of the assignment request shall also be applied for BSS internal and also UTRAN internal handover. For external handover, the MSC shall include the priority information in the handover request according to the definition in TS 48.008 (for GSM) and TS 25.413 (for UMTS) in the same way as for the assignment request.
eMLPP cannot be applied with standard GSM Phase 1 or Phase 2 Mobile Stations (non compatible Mobile Stations) with all service aspects. A dedicated Mobile Station (compatible Mobile Station) with eMLPP capability is required.
Specific functions a compatible Mobile Station shall provide are:
priority selection via MMI for call establishment in case of an eMLPP subscription including priority levels above level 4;
analysis of the priority level included in a paging message, Call Waiting indication or notification into a voice group call or voice broadcast call, respectively;
automatic reaction on basis of the analysed priority level in case of an incoming call while in dedicated mode, group transmit mode or group receive mode, respectively, according to the user defined Mobile Station configuration (for each subscribed priority level the user shall be able to configure the Mobile Station for automatic acceptation or indication or rejection of an incoming call);
However, if eMLPP is provided in a network, it can be applied to non compatible Mobile Stations in the following way:
calls of subscribers which have no specific eMLPP subscription shall be treated for resource pre-emption with a default priority level.
This shall also apply independent of the use of compatible or non compatible Mobile Stations;
calls of eMLPP subscribers which use a non compatible Mobile Station shall be treated for resource pre-emption with the subscriber's default priority level;
calls to eMLPP subscribers which use a non compatible Mobile Station shall be indicated to the user by Call Waiting as normal.
Information concerning the maximum priority level which a subscriber is entitled to use at call establishment shall be stored in the HLR.
If the maximum priority level is above level 4, one level shall be indicated as default level. This default level shall be used for mobile originated calls if no priority selection is performed by the user at call establishment.
The default selection can be performed by the subscriber by means of a registration procedure.
eMLPP may have the following logical states (refer to TS 23.011 for an explanation of the notation):
HLR Induction State
Not Active Not Induced)
Active and Operative Not Induced)
The HLR shall store the logical state of eMLPP (which shall be one of the valid states listed above) on a per subscriber basis.
The following figure shows the successful cases of transition between the applicable logical states of eMLPP. The state changes are caused by actions of the service provider.
Note that error cases are not shown in the diagram as they normally do not cause a state change. Additionally, some successful requests may not cause a state change. Hence they are not shown in the diagram.
If the provisioning state for eMLPP is "Provisioned" then, when the subscriber registers on a VLR, the HLR shall send that VLR information about the logical state of eMLPP, the maximum priority level and the default priority level.
If any of the eMLPP subscriber data is changed, the HLR shall send to the VLR the complete eMLPP subscriber data.
The network specific service configuration of eMLPP defined by the network operator as specified in TS 22.067 shall be stored within each MSC. This includes information on resource pre-emption actions for any given levels of incoming and on-going call priority. An example for a network specific service configuration is given in TS 22.067.
Each compatible Mobile Station shall be aware of the automatic answering actions for any given levels of priority so that when in idle mode or dedicated mode or group receive mode or group transmit mode, it can decide on the necessary reactions to be taken according to the priority information of the incoming call.
For this, the SIM shall store the following data:
Automatic answering applies
Fast set-up actions (note)
The automatic reaction of the Mobile Station for automatic answering or called party pre-emption shall be predefined by the user via MMI. For each subscribed priority level the user shall be able to configure the Mobile Station for automatic acceptation or indication or rejection of an incoming call.
In addition, the Mobile Station shall verify a priority level selected by the user at call establishment against the priority levels stored on the SIM and act accordingly as defined in subclause 220.127.116.11.
The Mobile Station shall perform automatically the related functions for a fast call set-up if related with a selected priority.
In the network, specific service configurations for VBS and VGCS calls which are registered in the GCR, a priority level shall be assigned to each voice broadcast call or voice group call configuration, according to TS 43.069 and TS 43.068, respectively.