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Content for  TS 23.379  Word version:  19.3.0

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10.19.3.2  Ad hoc group call involving multiple MC systemsp. 248

10.19.3.2.1  Procedure for ad hoc group call setup - Participants list provided by the Initiatorp. 248
Figure 10.19.3.2.1-1 illustrates the procedure for ad hoc group call setup procedure initiated by an authorized user wherein either a list of participants or an ad hoc group ID from an ad hoc group emergency alert is provided by the authorised user and the determined MCPTT users are from multiple MCPTT systems.
Pre-conditions:
  1. The security aspects of sharing the user information between primary and partner MC systems shall be governed as per the service provider agreement between them. In this case, it is considered that the partner MC system shares their users' information to the primary MC system.
  2. The authorized MCPTT user/dispatcher belongs to the primary MC system.
  3. The MCPTT server of the primary MC system is where the authorized MCPTT user/dispatcher controls the ad hoc group.
  4. Some users of the ad hoc group belong to partner MC systems.
  5. The preconfigured group identity and preconfigured group configuration to be used for an ad hoc group have been preconfigured in the MCPTT client and other participants of ad hoc group have also received the relevant security related information to allow them to communicate in an ad hoc group communication.
  6. If an ad hoc group ID from an ad hoc group emergency alert is used to invite the ad hoc group members, MCPTT client is aware of the ad hoc group ID.
Reproduction of 3GPP TS 23.379, Fig. 10.19.3.2.1-1: Ad hoc group call setup
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Step 1.
The MCPTT client of the authorized user initiates an ad hoc group call with multiple users from primary and partner MC systems. An ad hoc group call request message with the information of the MCPTT IDs or an ad hoc group ID if the ad hoc group call follows an ad hoc group emergency alert is routed to the MCPTT server of the primary MC system.
Step 2.
If the ad hoc group call is supported, the MCPTT server of the primary MC system verifies whether the user at of MCPTT client is authorized to initiate an ad hoc group call. If not authorized, the MCPTT server of the primary MC system rejects the ad hoc group call request as specified in the step 3. If the the MC service users' information received in step 1 does not contain an ad hoc group ID from an ad hoc group emergency alert, the MCPTT server of the primary MC system forms the ad hoc group by using MCPTT users' information received in step 1, determines the preconfigured group to be used for the configuration and assigns an MCPTT group ID for the newly formed ad hoc group. If no MC service ad hoc group ID was included in the ad hoc group call request of step 1, or if the provided MC service ad hoc group ID is not accepted by the MC service server, the MCPTT server assigns a MCPTT group ID for the newly formed ad hoc group.
The MCPTT server identifies the appropriate MCPTT server responsible for the MCPTT users of the ad hoc group. The MCPTT server considers the ad hoc group call participants as implicitly affiliated to the ad hoc group.
Step 3.
The MCPTT server shall send the ad hoc group call request return message to the MCPTT client containing the below:
  1. The MCPTT ad hoc group ID either generated by the MCPTT server or provided by the MCPTT client if the ad hoc group ID is from an ad hoc group emergency alert (only included when the ad hoc group call is authorized);
  2. The group ID of the pre-configured group to be used for the ad hoc group call (only included when the ad hoc group call is authorized); and
  3. Result of whether the ad hoc group call is authorized or not.
If the ad hoc group call request is not authorized, the MCPTT server and MCPTT client shall not proceed with the rest of the steps.
Step 4.
The MCPTT server of the primary MC system sends the ad hoc group call requests towards the MCPTT clients of the invited users belonging to the primary MC system based on step 1. While sending the ad hoc group call requests, the MCPTT server of the primary MC system shall remove the information elements that are not required to be conveyed to the target MCPTT clients (e.g. MCPTT ID list of the users who are required to acknowledge).
Step 5.
The receiving MCPTT clients notify their corresponding MCPTT users about the incoming ad hoc group call request with the information of the MCPTT group ID for the ad hoc group, and may accept or reject the call and respond with an adhoc group call response.
Step 6.
The primary MCPTT server further initiates an ad hoc group call request message to the MCPTT users of the partner MC system. The ad hoc group call request message is routed to the MCPTT users via the MCPTT server of the partner MC system.
Step 7.
The receiving MCPTT clients notify their corresponding MCPTT users about the incoming ad hoc group call request with the information of the MCPTT group ID for the ad hoc group. The MCPTT users upon receipt of the invitation may accept or reject the call, and respond with the ad hoc group call response. The ad hoc group call response message is routed to the MCPTT server of the primary MC system via the MCPTT server of the partner MC system.
Step 8.
The MCPTT server of the primary MC system provides an ad hoc group call response message to the MCPTT client of the authorized MCPTT user upon receiving response to the corresponding ad hoc group call request in step 1. The ad hoc group call response will consist of the success or failure result and/or detailed reason information in case of failure.
Step 9.
Upon successful ad hoc group call setup, a group call is established amongst the multiple group members from primary and partner MC systems. The media plane and floor control resources are established.
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10.19.3.2.2  Procedure for ad hoc group call release by MCPTT server - Participants list provided by the Initiatorp. 250
This procedure focuses on the case where an MCPTT server initiates the termination of an ongoing MCPTT ad hoc group call for all the participants of that group call, since at least one of the termination conditions are met e.g., due to hang time expiry, last participant leaving, second last participant leaving, initiator leaving, or minimum number of affiliated MCPTT group members are not present.
Procedures in Figure 10.19.3.2.2-1 are the signalling control plane procedures for the MCPTT server initiating termination of an ongoing MCPTT ad hoc group call.
Pre-condition:
  • The MCPTT client 1 and MCPTT client 2 belong to primary MC system. The MCPTT client 3 belongs to partner MC system.
Reproduction of 3GPP TS 23.379, Fig. 10.19.3.2.2-1: Ad hoc group call release
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Step 1.
The MCPTT users on MCPTT client 1, client 2 and client 3 are already part of the ongoing ad hoc group call (e.g. as a result of ad hoc group call setup as specified in clause 10.19.3.2.1).
Step 2.
The MCPTT server would like to release the ad hoc group call which is ongoing e.g., due to hang time expiry, last participant leaving, second last participant leaving, initiator leaving, or minimum number of affiliated MCPTT group members are not present.
Step 3.
The MCPTT server identifies the participants of the ongoing ad hoc group call and generates ad hoc group call release request to release ongoing session.
Step 4.
The MCPTT server sends a ad hoc group call release request via SIP core towards each participant of the ongoing group call. If the participants belong to partner MC system, then ad hoc group call release request is routed to the MCPTT clients of the partner MC system via the partner MCPTT server.
Step 5.
The MCPTT users are notified about the release of the ad hoc group call.
Step 6.
The MCPTT client(s) receiving ad hoc group call release request, send acknowledgement towards the MCPTT server by sending a ad hoc group call release response.
Step 7.
The MCPTT client 1, client 2 and client 3 have successfully released the floor control and media plane resources associated with the ad hoc group call that is terminated. The MCPTT servers remove the ad hoc group information from the dynamic data held in the MCPTT servers and the ad hoc group ceases to exist, otherwise if the ad hoc group call follows an ad hoc group emergency alert the MCPTT servers keep the dynamic data and the ad hoc group continues to exist.
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10.19.3.2.3  Ad hoc group call setup - Participants list determined by the MCPTT serverp. 251
Figure 10.19.3.2.3-1 below illustrates the ad hoc group call setup procedure initiated by an authorized user wherein the list of participants is determined by the MCPTT server based on the criteria received from the MCPTT client and determined MCPTT users are from multiple MCPTT systems.
Pre-conditions:
  1. The security aspects of sharing the user information between primary and partner MC systems shall be governed as per the service provider agreement between them. In this case, it is considered that the partner MC system share their users' information to the primary MC system.
  2. The authorized MCPTT user/dispatcher belongs to the primary MC system.
  3. The MCPTT server 1 of the primary MC system is where the authorized MCPTT user/dispatcher creates the ad hoc group.
  4. Some users of the ad hoc group belong to MCPTT server 2 of the partner MC systems.
  5. The pre-configured group identity and pre-configured group configuration to be used for an ad hoc group have been preconfigured in MCPTT client and other participants of ad hoc group have also received the relevant security related information to allow them to communicate in an ad hoc group communication.
Reproduction of 3GPP TS 23.379, Fig. 10.19.3.2.3-1: Ad hoc group call setup involving multiple MCPTT systems
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Step 1-3.
Same as described in subclause 10.19.3.1.3.
Step 4.
The MCPTT server 1 determines the list of participants from the primary MC system and determines the partner MC system to be involved in the ad hoc group call based on the information present in the information element Criteria for determining the participants. This information element carries the criteria, indicator identifying pre-defined criteria, or a combination of both.
Step 5.
If the MCPTT server 1 needs to involve the partner system based on the agreement and based on the criteria for determining the participant list, it sends the ad hoc group call get userlist request to the MCPTT server 2. This request carries the criteria specified in the step 1.
Step 6.
MCPTT server 2 evaluates the criteria and determines the participants satisfying the criteria (i.e., MCPTT client 3 and MCPTT client 4) and sends the response containing the list of MCPTT users satisfying the criteria. The partner MCPTT server may apply local policies if any while determining the participants satisfying the criteria.
Step 7.
The MCPTT server 1 compiles the list of participants to be invited for the ad hoc group call including the participants from both primary and partner MC system.
Step 8a-8b.
The MCPTT server 1 sends the ad hoc group call request towards the MCPTT client 3 and MCPTT client 4. While sending the ad hoc group call request, the MCPTT server shall remove the information elements that are not required to be conveyed to the target MCPTT clients. This request carries the pre-configured group ID whose configuration is to be applied for this ad hoc group call if end-to-end encryption is requested. The MCPTT server 1 considers the ad hoc group call participants as implicitly affiliated to the ad hoc group.
Step 9.
The MCPTT server 1 sends the ad hoc group call requests towards the MCPTT client 2. While sending the ad hoc group call request, the MCPTT server shall remove the information elements that are not required to be conveyed to the target MCPTT clients. This request carries the pre-configured group ID whose configuration is to be applied for this ad hoc group call if end-to-end encryption is requested. The MCPTT server 1 considers the ad hoc group call participants as implicitly affiliated to the ad hoc group.
Step 10a-10c.
The receiving MCPTT clients notify their corresponding MCPTT user about the incoming ad hoc group call request with the information of the MCPTT group ID for the ad hoc group.
Step 11.
The MCPTT client 2 may accept or reject the ad hoc group call request and send ad hoc group call response to the MCPTT server 1.
Step 12.
The MCPTT client 3 may accept or reject the ad hoc group call request, and sends ad hoc group call response to the MCPTT server 1.
Step 13.
The MCPTT client 4 may accept or reject the ad hoc group call request, and sends ad hoc group call response to the MCPTT server 1.
Step 14.
The MCPTT server 1 sends the ad hoc group call response to MCPTT client 1 through the signalling path to inform about successful call establishment.
Step 15.
The MCPTT server 1 may notify the initiating MCPTT user of all MCPTT users who acknowledged the ad hoc group call request and joined the ad hoc group call. The MCPTT server 1 more than once during the call may send this notification to the initiating MCPTT user whenever an MCPTT user joins or leaves the MCPTT ad hoc group call. The authorized users (not shown in figure), who are configured to receive the participants information of ad hoc group call, are notified to receive the MCPTT IDs of the MCPTT users who acknowledged the ad hoc group call request and joined the ad hoc group call, when the MCPTT users joins late or leave the MCPTT ad hoc group call.
Step 16.
The MCPTT client 1, MCPTT client 2, MCPTT client 3 and MCPTT client 4 establish media plane and floor control resources.
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