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Content for  TS 23.283  Word version:  18.1.0

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10.3.3  Pre-arranged group callp. 40

10.3.3.1  Generalp. 40

The subclause 10.3.3.2 and subclause 10.3.3.3 describe the group call setup between the MCPTT system and the LMR system on an interworking group defined in the MCPTT system. The subclause 10.3.3.4 and subclause 10.3.3.5 describe the group call setup between the MCPTT system and the LMR system on an interworking group defined in the LMR system. The subclause 10.3.3.7 describes the late entry procedures and subclause 10.3.3.8 describes the group call release procedures. Group calls can use MC media encryption between the IWF and the MCPTT clients as described in TS 33.180. A call that uses an LMR vocoder may use LMR E2EE if the calling and called parties have previously been provisioned with the appropriate LMR E2EE keys.
The procedures in the present subclause are applicable to the following non-broadcast group call types: pre-configured group regroup calls, pre-configured user regroup calls and group regroup calls.
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10.3.3.2  Group call setup initiated by MCPTT user on an interworking group defined in MCPTT systemp. 41

In this procedure, an MCPTT user is initiating a group call on an interworking group defined in the MCPTT system. The signalling procedure is described in Figure 10.3.3.2-1.
This subclause is based upon subclause for pre-arranged group call setup in subclause 10.6.2.3.1.1.2 of TS 23.379.
Pre-conditions:
  1. The interworking group information is known at the MCPTT server and the IWF by configuration or group creation. The interworking group has been defined in the MCPTT system.
  2. MCPTT client 1 and MCPTT client 2 are registered and their respective users are authenticated and authorized to use the MCPTT service.
  3. The users in this interworking group have been affiliated to the group.
  4. The mapping relationship of group and user identities between the MCPTT system and the LMR system has been configured at the IWF.
Copy of original 3GPP image for 3GPP TS 23.283, Fig. 10.3.3.2-1: Group call setup initiated by MCPTT user on an interworking group defined in MCPTT system
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Step 1.
MCPTT user at MCPTT client 1 initiates a group call for the selected interworking group identified by MCPTT group ID.
Step 2.
MCPTT client 1 sends a group call request to the MCPTT server.
Step 3.
MCPTT server checks whether the user of MCPTT client 1 is authorized to initiate a group call on the selected interworking group.
Step 4.
MCPTT server proceeds group call setup procedures towards the affiliated MCPTT system users as described in TS 23.379.
Step 5.
MCPTT server sends IWF group call request(s) towards the IWF. If the IWF has affiliated to this group on behalf of the group's LMR users, only one IWF group call request message is sent to the IWF. If the MCPTT server has received individual affiliations from the group's LMR users, an individual IWF group call request is sent (to the IWF) for each affiliated LMR user.
Step 6.
The IWF returns IWF group call response(s) to the MCPTT server. If E2EE is specified, then the MCPTT users and the LMR users shall use the same codec. If E2EE is not specified, the MCPTT users and the LMR users can use different codecs and transcoding is needed at the IWF.
Step 7.
The MCPTT server sends group call response to the MCPTT client 1 about successful call establishment.
Step 8.
The group call on the interworking group has successfully established media plane for communication and any user can transmit media. The MCPTT system where the interworking group is defined is the controlling system of the group call and manages the floor control.
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10.3.3.3  Group call setup initiated by LMR user on an interworking group defined in MCPTT system.p. 42

In this procedure, an LMR user is initiating a group call on an interworking group defined in the MCPTT system. The signalling procedure is described in Figure 10.3.3.3-1.
This subclause is based upon subclause for pre-arranged group call setup in subclause 10.6.2.3.1.1.2 of TS 23.379.
Pre-conditions:
  1. The interworking group information is known at the MCPTT server and the IWF by configuration or group creation. The interworking group has been defined in MCPTT system.
  2. MCPTT client 1 and MCPTT client 2 are registered and their respective users are authenticated and authorized to use the MCPTT service.
  3. The users in this interworking group have been affiliated to the interworking group.
  4. The mapping relationship of group and user identities between the MCPTT system and the LMR system has been configured at the IWF.
  5. LMR user initiates a group call.
Copy of original 3GPP image for 3GPP TS 23.283, Fig. 10.3.3.3-1: Group call initiated by LMR user on an interworking group defined in MCPTT system
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Step 1.
The IWF sends an IWF group call request to the MCPTT server for call establishment. If floor control is requested by the calling LMR user, an indication of implicit floor request is included. If the group call request contains an implicit floor request it may also include location information.
Step 2.
MCPTT server calls the affiliated users from MCPTT system as described in TS 23.379. If E2EE is specified, then the MCPTT users and the LMR users shall use the same codec. If E2EE is not specified, the MCPTT users and the LMR users can use different codecs and transcoding is needed at the IWF.
Step 3.
If the group has other affiliated LMR users than the calling party and the MCPTT server has received individual affiliations from those LMR users, an individual IWF group call request is sent to the IWF for each affiliated LMR user.
Step 4.
The IWF returns IWF group call response(s) to the MCPTT server.
Step 5.
The MCPTT server confirms the successful establishment of the group call by sending an IWF Group call response to the IWF.
Step 6.
The interworking group call has successfully established media plane for communication and any user can transmit media. The MCPTT system where the interworking group is defined is the controlling system of the group call and manages the floor control.
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10.3.3.4  Group call setup initiated by MCPTT user on an interworking group defined in the LMR systemp. 43

In this procedure, an MCPTT user is initiating a group call on an interworking group defined in the LMR system. The signalling procedure is described in Figure 10.3.3.4-1.
This subclause is based upon subclause for Pre-arranged group call setup in subclause 10.6.2.3.1.1.2 of TS 23.379.
Pre-conditions:
  1. The interworking group information is known at the MCPTT Server and the IWF by configuration or group creation. The interworking group has been defined in the LMR system.
  2. MCPTT client 1 and MCPTT client 2 are registered and their respective users are authenticated and authorized to use the MCPTT service.
  3. The users in this interworking group have been affiliated to the group.
  4. The mapping relationship of group and user identities between the MCPTT system and the LMR system has been configured at the IWF.
Copy of original 3GPP image for 3GPP TS 23.283, Fig. 10.3.3.4-1: Group call initiated by MCPTT user on an interworking group defined in the LMR system
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Step 1.
MCPTT user at MCPTT client 1 initiates a group call on the selected interworking group identified by MCPTT group ID.
Step 2.
MCPTT client 1 sends a group call request to the MCPTT server.
Step 3.
As the interworking group is defined in the LMR system the MCPTT server sends an IWF group call request to the IWF.
Step 4.
The IWF sends individual IWF group call request(s) to the MCPTT server for each affiliated MCPTT user in the group, in this example scenario to the user in MCPTT client 2.
Step 5.
The MCPTT server sends a group call request to the MCPTT client 2.
Step 6.
The MCPTT client 2 acknowledges towards the MCPTT server by sending a group call response.
Step 7.
The MCPTT server acknowledges towards the IWF by sending an IWF group call response.
Step 8.
The IWF sends an IWF group call response to the MCPTT server to acknowledge the IWF group call request received in step 3.
Step 9.
The MCPTT server sends a group call response to the initiating MCPTT user. If E2EE is specified, then the MCPTT users and the LMR users shall use the same codec. If E2EE is not specified, the MCPTT users and the LMR users can use different codecs and transcoding is needed at the IWF.
Step 10.
The group call over the interworking group has successfully established media plane for communication and any user can transmit media. The LMR system where the interworking group is defined is the controlling system of the group call and manages the floor control.
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10.3.3.5  Group call setup initiated by LMR user on an interworking group defined in the LMR system.p. 45

In this procedure, an LMR user is initiating a group call on an interworking group defined in the LMR system. The signalling procedure is described in Figure 10.3.3.5-1.
This subclause is based upon subclause for Pre-arranged group call setup in subclause 10.6.2.3.1.1.2 of TS 23.379.
Pre-conditions:
  1. The interworking group information is known at the MCPTT Server and the IWF by configuration or group creation. The interworking group has been defined in the LMR system.
  2. MCPTT client 1 and MCPTT client 2 are registered and their respective users are authenticated and authorized to use the MCPTT service.
  3. The users in this interworking group have been affiliated to the group.
  4. The mapping relationship of group and user identities between the MCPTT system and the LMR system has been configured at the IWF.
  5. LMR user initiates a group call.
Copy of original 3GPP image for 3GPP TS 23.283, Fig. 10.3.3.5-1: Group call initiated by LMR user on an interworking group defined in the LMR system
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Step 1.
The IWF sends an IWF group call request(s) to the MCPTT server for call establishment. An individual IWF group call request is sent to the MCPTT server for each affiliated MCPTT user in the group, in this example scenario to the users in MCPTT clients 1 and 2. If floor control is requested by the calling LMR user, an indication of implicit floor request is included. If the group call request contains an implicit floor request it may also include location information.
Step 2.
MCPTT server sends a group call request(s) to the target MCPTT user(s) as described in TS 23.379.
Step 3.
MCPTT client(s) receiving the group call request, acknowledge towards the MCPTT server by sending a group call response.
Step 4.
The MCPTT server acknowledges the IWF group call request(s) by sending a IWF group call response(s) to the IWF. If E2EE is specified, then the MCPTT users and the LMR users shall use the same codec. If E2EE is not specified, the MCPTT users and the LMR users can use different codecs and transcoding is needed at the IWF.
Step 5.
The interworking group call has successfully established media plane for communication and any user can transmit media. The LMR system where the interworking group is defined is the controlling system of the group call and manages the floor control.
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10.3.3.6  Encrypted group call with transcodingp. 46

Pre-conditions:
  1. An MCPTT session is established between an MCPTT client, the interworked LMR system (represented by the IWF), and the MCPTT server.
  2. There is an ongoing media transmission.
  3. An SDP negotiation has occurred between the IWF and MCPTT Server to establish both the vocoder and the security parameters for the call.
  4. The IWF is configured to perform transcoding of voice media and has obtained key material from the MCPTT system using the procedures in TS 33.180.
Copy of original 3GPP image for 3GPP TS 23.283, Fig. 10.3.3.6-1: Encrypted group call with transcoding
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Step 1.
The MCPTT client has been given the floor and is transmitting voice media.
Step 2.
The MCPTT client encodes audio using a codec defined for the MCPTT group, encrypts the encoded voice using procedures in TS 33.180, and forwards the encrypted voice media to the MCPTT server.
Step 3.
The MCPTT server forwards the encrypted voice media to other participants in the group call including the IWF.
Step 4.
The IWF decrypts the voice media from the MCPTT client using the procedures in TS 33.180. The IWF transcodes the voice to a LMR codec. If needed, the IWF re-encrypts the transcoded voice media using LMR security procedures (these are out-of-scope of this specification), and forwards the voice media to the LMR system.
Step 5.
Sometime later the floor becomes idle.
Step 6.
The LMR system (represented by the IWF in Figure 10.3.3.6-1) requests and is granted the floor.
Step 7.
The IWF has been given the floor and is transmitting voice media.
Step 8.
The IWF receives voice media from the LMR system. If the voice media is encrypted, the IWF decrypts the voice media using LMR security procedures (these are out-of-scope of this specification). The IWF transcodes the voice to the group's MCPTT codec. The IWF re-encrypts the transcoded voice using the procedures in TS 33.180.
Step 9.
The IWF forwards the voice media to the MCPTT server.
Step 10.
The MCPTT server forwards the voice media to other participants in the group call.
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