11 Functions and information flow

03.673GPPenhanced Multi Level Precedence and Pre-emption service (eMLPP)Stage 2TS

11.1 Subscription

When the subscriber record is created in the HLR, the maximum priority level a subscriber is entitled to use shall be included.

11.2 Change of subscription

The network operator can change the maximum priority level of any eMLPP subscriber at any time. A change of subscription shall not affect any on-going calls at the moment of change. The subscriber cannot change the maximum priority level via the MMI.

11.3 Call set-up

11.3.1 Mobile originated calls

11.3.1.1 Indication of priority

The Mobile Station may indicate the priority of each call initiated. If no priority is indicated by the user or a non-compatible Mobile Station is used then the default priority level shall be applied which is stored in the VLR. The selection of priority shall be an MMI function.

Mobile stations indicate the priority of their call in the signalling that takes place during the call establishment process.

No preferential treatment will be possible during this initial random access until the point at which the priority information is received by the network (CM_SERV_REQ message). Alternatively, a resource pre-emption might already take place on basis of an establishment cause.

Prior to the indication of the selected priority level in the CM_SERV_REQ message, the BSC may decide on the assignment of an SDCCH or direct assignment of a TCH on the basis of the establishment cause in the CHAN_REQ message. This allows the BSC to support a fast call set-up at the earliest stage of the call establishment. The establishment cause for emergency calls or an establishment cause indicating the request for fast call set-up shall be able to trigger this function.

11.3.1.2 Subscription checking

The Mobile Station shall verify the selected priority level against the priority levels stored in the SIM. If the selected priority is not allowed, then the priority of the call shall be modified to that of the nearest allowed priority level below the requested level.

The MSC shall request the VLR to verify if the subscriber is allowed to use the selected priority level.

11.3.1.3 Authentication and ciphering

The network may wish to omit or postpone authentication and ciphering in order to provide for a faster call set-up.

If the network decides to omit or postpone authentication and ciphering for a call it can send a CM_SERV_ACC message in reply to the CM_SERV_REQ message.

11.3.1.4 Indication of priority to the BSC

The channel assignment request to the BSC shall also include the priority level and pre-emption capability of the connection as defined in GSM 08.08. The MSC maps the eMLPP priority on these priority levels. In addition, the eMLPP priority shall be explicitly indicated to the BSC in the assignment request. The BSC shall store the priority level in order to decide on later actions, e.g. to arrange notifications to the Mobile Station according to priorities.

11.3.1.5 Choice of radio channel

If an appropriate radio channel is available the BSC shall assign it as normal. If no channels are available then the BSC shall perform queuing according to the priority levels. If the assignment request has a pre-emption capability indicator, pre-emption shall be performed.

In addition, the network related service configuration defines the set-up class in relation to a priority level and therefore the allowable delay of the call establishment (see GSM 02.67). By using this information, the MSC shall decide whether OACSU may be applied for a call or not.

11.3.1.6 Indication of priority to the Mobile Station

If the network assigns a priority level to the call different to the one requested by the user for any reasons or if the Mobile Station does not know what priority level will be applied since no priority was included in the service request, the network can inform the Mobile Station on the assigned priority level by sending a CALL_PROCEEDING message including a priority information element.

The Mobile Station shall store the priority level requested by the user, possibly overridden by the level received by the network, to perform automatic answering of calls or pre-emption of on-going calls.

11.3.2 Mobile terminated calls

11.3.2.1 Indication of priority

For a mobile terminated call, the priority level is defined in the ISUP set-up message to the VMSC. The priority and pre-emption indications used in the ISUP shall follow the definitions of the MLPP service as defined in the ITU-T recommendations Q.85 and Q.735, respectively

In GSM, a PAGING REQUEST message on CCCH may also include a priority level as described in GSM 04.08 [10], subsection ‘Paging initiation using paging subchannel on CCCH’.

NOTE: Mobile stations in idle mode which are going to respond to a paging message do not need to analyse the priority level in the paging request message but can take the priority level provided in the set-up message. Mobile stations in group receive mode or an MS in class-B mode that communicates on GPRS radio channels when a dedicated channel is needed need to analyse the priority level in the paging request message in order to decide to respond to the paging request. (see TS 23.060 subsection ‘GPRS and Dedicated Mode Priority Handling’).

11.3.2.2 Indication of priority to the BSC

The channel assignment request to the BSC shall include the priority level and pre-emption capability of the connection as defined in GSM 08.08. The MSC maps the eMLPP priority on these priority levels. In addition, the eMLPP priority shall be explicitly indicated to the BSC in the assignment request. The BSC shall store the priority level in order to decide on later actions, e.g. to arrange notifications to the Mobile Station according to priorities.

11.3.2.3 Authentication and ciphering

The network may wish to omit or postpone authentication and ciphering in order to provide for a faster call set-up according to the priority level to be applied for the call and the network specific service configuration stored in the MSC.

If the network decides to omit or postpone authentication and ciphering for a call it, can send the SETUP message immediately after reception of the initial layer 3 message.

11.3.2.4 Termination with called subscriber in idle mode or group receive mode

In this case the Mobile Station shall be paged in the normal manner, but with the paging messages also containing the priority level of the call. In addition, the priority level will be provided with the SETUP message.

The Mobile Station in group receive mode shall consult the internal service configuration list stored on the SIM to establish whether it should automatically respond to the paging request.

The Mobile Station in idle mode does not need to analyse the priority level from the paging request message but can derive it from the SETUP message and then decide on automatic acceptance of the call.

In the case where the called subscriber is using a non compatible Mobile Station, automatic answering is not possible.

11.3.2.5 Termination with called subscriber in dedicated mode

In the case where the called subscriber has a subscription for eMLPP and for Call Waiting and is using a compatible Mobile Station, the Mobile Station shall be informed of the priority of the new call together with the call waiting indication. The Mobile Station will then consult the internal service configuration list stored on the SIM to establish whether it should automatically accept the waiting call without consulting the user, or whether the call waiting facility will be used as normal.

In the case where the called subscriber has no subscription for Call Waiting, called party pre-emption is not possible.

In the case where the called subscriber is using a non compatible Mobile Station and has a subscription for Call Waiting, Call Waiting shall be performed as normal.

11.3.3 Voice group call or voice broadcast call

11.3.3.1 Indication of priority to the related MSC

For each voice group call or voice broadcast call service configuration registered in the GCR as defined in GSM 03.68 and GSM 03.69, respectively, a priority level is assigned at registration of the GCR data by the service provider. The priority level will be provided by the GCR together with the call attributes.

11.3.3.2 Authentication and ciphering

Authentication of the calling service subscriber shall be performed equivalent to the standard mobile originated call case as defined in subclause 11.5.1.3. The calling service subscriber shall be treated with his selected priority or with his default priority as known in the VLR as long as he has an own link with the network (see GSM 03.68 and GSM 03.69). The priority which applies to the voice group call channel or voice broadcast call channel is defined in the GCR.

Authentication and ciphering of the calling service subscriber might therefore be performed, omitted or postponed (see subclause 11.3.1.3).

11.3.3.3 Indication of priority to the called Mobile Stations

The priority level shall be indicated together with the related paging messages or notification messages and treated in the Mobile Station as defined in GSM 03.68 and GSM 03.69, respectively.

11.4 Pre-emption

11.4.1 Choice of communication to pre-empt

For all resources where pre-emption may be required, namely radio channels, A-interface channels and inter switch trunks, the network specific service configuration stored within the MSC shall be used to determine whether pre-emption should occur, and if so, which communication to pre-empt. The MSC shall inform the BSS about priority and pre-emption by using the priority message element in the assignment request as defined in GSM 08.08. Mapping of the priority information in this message element on the network specific eMLPP configuration shall be performed in the MSC.

11.4.2 Release procedures

Suitable messages shall be passed from the point at which the pre-emption is to occur, to other affected entities. In the case of fast call set-up, such pre-indication may need to be foregone to meet the required set-up time.

The indication to the pre-empted user shall be performed by an indication for congestion as defined in GSM 02.40.

11.5 Pre-emption at handover

When an on-going call is handed over into a fully used cell, the BSC shall perform queuing and pre-emption if necessary according to the priority and pre-emption capability information received with the assignment request.

In case of BSS external handover, the priority and pre-emption capability information shall be included in the handover request as defined in GSM 08.08.

11.6 Overview of call related signalling

In this overview, the message structure to implement the specified concept are identified, and brief details are given of each message.

A diagrammatic representation of the transport procedures to be used to carry the priority information in case of standard point-to-point calls are given in figures 1 to 6. The message flow is not represented completely.

The corresponding message flows in case of voice group calls or voice broadcast calls are given in GSM 03.68 and GSM 03.69, respectively.

Figure 1: Signalling information required for the prioritisation at mobile originating call establishment without fast call set-up

Initial RACH CHAN_REQ: Standard message.

IMM_ASS: Standard message.

SABM (SERV_REQ): Modified form of the current L3-MM CM SERVICE REQUEST where the priority level is provided in addition if a priority selection is performed by the user. In case of no priority selection or use of a non-compatible Mobile Station the Mobile Station shall send a standard service request message and the network shall apply a default priority to their request.

UA (SERV_REQ): Standard message.

COM_L3_INFO: The MSC is provided with initial information about the requested service together with the selected priority level if applicable.

AUTH_REQ: Standard message.

AUTH_RES: Standard message.

CIPH_MOD_CMD: Standard message.

CIPH_MOD_COM: Standard message.

SETUP: Standard message.

CALL_PROCEEDING: The network may include the assigned priority level in a CALL_PROCEEDING message if no priority level was indicated in the CM_SERVICE_REQUEST message or the assigned priority level is different to the one requested.

ASS_REQ: This message is sent from the MSC to the BSC including the call priority and pre-emption capability to be applied as defined in GSM 08.08, according to the priority information the MSC has obtained from the service request or from the VLR data. In addition, the eMLPP level is included as explicit information.

ASS_CMD: Standard message.

SABM: Standard message.

UA: Standard message.

ASS_COM: Standard message.

Figure 2: Signalling information required for the prioritisation at mobile originating call establishment with fast call set-up

SYSTEM INFO: The network may provide information on the BCCH system information, that a MM connection is provisional granted after establishment of the main signalling link.

If such information is provided on the BCCH and the user has selected a fast call set-up, the Mobile Station shall immediately send a SETUP message to the network after the main signalling link is established.

Initial RACH CHAN_REQ: Standard message.

IMM_ASS: Standard message.

SABM (SERV_REQ): Modified form of the current L3-MM CM SERVICE REQUEST where the priority level is provided in addition if a priority selection is performed by the user.

UA (SERV_REQ): Standard message.

COM_L3_INFO: The MSC is provided with initial information about the requested service together with the selected priority level if applicable.

If the network itself decides not to perform ciphering, it shall send an CM_SERV_ACC message.

SETUP: Standard message.

CALL_PROCEEDING: The network may include the assigned priority level in a CALL_PROCEEDING message if no priority level was indicated in the CM_SERVICE_REQUEST message or the assigned priority level is different to the one requested.

ASS_REQ: This standard message is sent from the MSC to the BSC including the call priority and pre-emption capability to be applied as defined in GSM 08.08, according to the priority information the MSC has obtained from the service request or from the VLR data. In addition, the eMLPP level is included as explicit information.

CHAN_MOD_MODIFY: Standard message.

CHAN_MOD_MODIFY_ACK: Standard message.

Figure 3: Signalling information required for the prioritisation at mobile terminating call establishment without fast call set-up and without called-party pre-emption

SETUP (prec.) req. ind.: In addition to the basic call requirements, the contents of the set-up information flow shall contain the information on the requested MLPP priority level.

PAGING: Modified paging command including the priority level to be applied.

PAG_REQ: Modified paging message including the related priority level.

Initial RACH CHAN_REQ: Standard message.

IMM_ASS: Standard message.

SABM (PAG_RSP): Standard message.

UA (PAG_RSP): Standard message.

PAG_RSP: Standard message.

AUTH_REQ: Standard message.

AUTH_RES: Standard message.

CIPH_MOD_CMD: Standard message.

CIPH_MOD_COM: Standard message.

SETUP: Standard message.

CALL_CONF: Standard message.

ASS_REQ: This standard message is sent from the MSC to the BSC including the call priority and pre-emption capability to be applied as defined in GSM 08.08, according to the priority information the MSC has obtained from the incoming set-up message. In addition, the eMLPP level is included as explicit information.

ASS_CMD: Standard message.

SABM: Standard message.

UA: Standard message.

ASS_COM: Standard message.

Figure 4: Signalling information required for the prioritisation at mobile terminating call establishment with fast call set-up and without called-party pre-emption

SETUP (prec.) req. ind.: In addition to the basic call requirements, the contents of the set-up information flow shall contain the information on the requested MLPP priority level.

PAGING: Modified paging command including the priority level to be applied.

PAG_REQ: Modified paging message including the related priority level.

Initial RACH CHAN_REQ: Standard message. A new establishment cause shall be provided to indicate the requirement for the direct assignment of a TCH (very early assignment) for the support of fast call set-up procedure.

IMM_ASS: Standard message.

SABM (PAG_RSP): Standard message.

UA (PAG_RSP): Standard message.

PAG_RSP: Standard message.

For fast call set-up the network shall immediately send a SETUP message to the Mobile Station. Authentication and ciphering may not be performed or delayed by the network.]

SETUP: Modified message with an indication of the priority level.

CALL_CONF: Standard message.

ASS_REQ: This standard message is sent from the MSC to the BSC including the call priority and pre-emption capability to be applied as defined in GSM 08.08, according to the priority information the MSC has obtained from incoming set-up message. In addition, the eMLPP level is included as explicit information.

CHAN_MOD_MODIFY: Standard message.

CHAN_MOD_MODIFY_ACK: Standard message.

Figure 5: Signalling information required for the called-party pre-emption in case of an existing telephony call and subscription for HOLD

Call Waiting should always be subscribed together with eMLPP. If not, no called party pre-emption is possible for point-to-point calls.

SETUP (prec.) req. ind.: In addition to the basic call requirements, the contents of the set-up information flow shall contain the information on the requested MLPP priority level.

SETUP: Modified SETUP message with an indication of the priority level.

CALL_CONF: Standard message with cause user busy.

On reception of the SETUP message a compatible Mobile Station decides on called party pre-emption. If called party pre-emption applies, the Mobile Station shall automatically accept the waiting call and put the other call on hold.

A non compatible Mobile Station shall not be harmed by the priority information and shall perform Call Waiting functions as normal.

ALERT: Standard message. ALERTING may be omitted in case of called party pre-emption.

HOLD: Standard message.

HOLD_ACK: Standard message.

CONNECT: Standard message.

CONN_ACK: Standard message.

NOTE: In case of an incoming data call a mode modify procedure has to be performed which is not included in figure 5.

Figure 6: Signalling information required for the called-party pre-emption in case of point-to-point data calls or no subscription for HOLD

Call Waiting should always be subscribed together with eMLPP. If not, no called party pre-emption is possible for point-to-point calls.

SETUP (prec.) req. ind.: In addition to the basic call requirements, the contents of the set-up information flow shall contain the information on the requested MLPP priority level.

SETUP: Modified SETUP message with an indication of the priority level.

CALL_CONF: Standard message with cause user busy.

On reception of the SETUP message a compatible Mobile Station decides on called party pre-emption. If called party pre-emption applies, the Mobile Station shall automatically accept the waiting call and clear the existing data call.

A non compatible Mobile Station shall not be harmed by the priority information and shall perform Call Waiting functions as normal.

ALERT: Standard message. ALERTING may be omitted in case of called party pre-emption.

RELEASE_COM: Standard message which shall be send immediately after the ALERT with a new cause for called party pre-emption.

CONNECT: Standard message.

CONN_ACK: Standard message.

11.7 Overview of call independent signalling

11.7.1 Registration

At the beginning of registration subscription, provision of the supplementary service and sufficiency of registration information has to be checked.

The default priority level has to be registered in the network.

When the mobile subscriber registers eMLPP, the network shall attempt to register the service. The network will return notification of acceptance of the request. This notification will include the default priority level.

If the system cannot accept a registration request, the network sends a notification that eMLPP registration was not successful to the served mobile subscriber.

The information flow for registration of eMLPP is shown in figure 7.

Figure 7: Registration of eMLPP

11.7.2 Interrogation

The mobile subscriber can request the status of the supplementary service, the maximum and default priority levels and be informed if the service is provided to him/her and on the actual maximum and default priority levels. This procedure is illustrated in figure 8.

Figure 8: Interrogation of eMLPP

Annex A (informative):
Change Request History

Change history

Date

TSG #

TSG Doc.

CR

Rev

Subject/Comment

Old

New

No phase 1 version

June 1994

TS for information to SMG#11

1.0.0

July 1995

TS approved by SMG#15

1.0.0

4.0.0

October 1995

TS changed to Phase 2+ TS

4.0.0

5.0.0

October 1996

CR 03.67-A001r2 (category B) approved by SMG#20
CR 03.67-A002r1 (category D)
CR 03.67-A003r1 (category B)

5.0.0

5.1.0

December 1996

GTS converted to draft prETS 300 932

5.1.0

5.1.0

May 1997

ETS 300 924 first edition

5.1.0

5.1.1

January 1999

Release 1997 version

5.1.1

6.0.0

August 1999

Release 1998 version

6.0.0

7.0.0

March 2000

CR 03.67-A005 (category A) approved by CN#07

7.0.0

7.1.0

December 2000

10

NP-000722

A006

3

Correction of Pre-emption service (eMLPP)

7.1.0

7.2.0

December 2000

10

Conversion to 3GPP layout

7.1.0

7.2.0