10.15 First-to-answer call setup
23.3793GPPFunctional architecture and information flows to support Mission Critical Push To Talk (MCPTT)Release 18Stage 2TS
10.15.1 Description
Figure 10.15.3-1 describes the basic procedure for the MCPTT client initiating MCPTT first-to-answer call. The flow may use a floor request in the MCPTT call request indicating that the originator will be given the floor when the call starts and eliminates the need for a separate initial floor request message during media plane establishment. Alternatively, the call initiation may be sent without the floor request, which allows the called party to request the floor first. For a MCPTT first-to-answer call without floor control, floor control is not established.
Figure 10.15.3-1 also describes the handling of private calls when a functional alias replaces the MCPTT ID as target address. A functional alias can be simultaneously used by more than one MCPTT user, i.e. multiple MCPTT clients can activate the same functional alias.
10.15.2 Information flows for first-to-answer call
10.15.2.1 MCPTT first-to-answer call request (MCPTT client to MCPTT server)
Table 10.15.2.1-1 describes the information flow MCPTT first-to-answer call request from the MCPTT client to the MCPTT server.
Table 10.15.2.1-1: MCPTT first-to-answer call request (MCPTT client to MCPTT server) information elements
|
Information Element |
Status |
Description |
|
MCPTT ID |
M |
The MCPTT ID of the calling party |
|
Functional alias |
O |
The functional alias of the calling party |
|
MCPTT ID list (see NOTE) |
O |
The list of MCPTT IDs of the called party |
|
Functional alias (see NOTE) |
O |
The functional alias of the called party |
|
Use floor control indication |
M |
This element indicates whether floor control will be used for the private call. |
|
SDP offer |
O |
Media parameters of MCPTT client. |
|
Implicit floor request |
O |
An indication that the user is also requesting the floor. |
|
Location information |
O |
Location of the calling party |
|
NOTE: At least one identity must be present. |
||
10.15.2.2 MCPTT first-to-answer call request (MCPTT server to MCPTT client)
Table 10.15.2.2-1 describes the information flow MCPTT first-to-answer call request from the MCPTT server to the MCPTT client.
Table 10.15.2.2-1: MCPTT first-to-answer call request (MCPTT server to MCPTT client) information elements
|
Information Element |
Status |
Description |
|
MCPTT ID |
M |
The MCPTT ID of the calling party |
|
Functional alias |
O |
The functional alias of the calling party |
|
MCPTT ID |
M |
The MCPTT ID of the called party |
|
Functional alias |
O |
The functional alias of the called party |
|
Use floor control indication |
M |
This element indicates whether floor control will be used for the private call. |
|
SDP offer |
M |
Media parameters of MCPTT client. |
|
Implicit floor request |
O |
An indication that the user is also requesting the floor. |
10.15.2.3 MCPTT first-to-answer call response (MCPTT client to MCPTT server)
Table 10.15.2.3-1 describes the information flow MCPTT first-to-answer call response from the MCPTT client to the MCPTT server.
Table 10.15.2.3-1: MCPTT first-to-answer call response (MCPTT client to MCPTT server) information elements
|
Information Element |
Status |
Description |
|
MCPTT ID |
M |
The MCPTT ID of the calling party |
|
Functional alias |
O |
The functional alias of the calling party |
|
MCPTT ID |
M |
The MCPTT ID of the called party |
|
Functional alias |
O |
The functional alias of the called party |
|
SDP answer |
M |
Media parameters selected |
10.15.2.4 MCPTT first-to-answer call response (MCPTT server to MCPTT client)
Table 10.15.2.4-1 describes the information flow MCPTT first-to-answer call response from the MCPTT server to the MCPTT client.
Table 10.15.2.4-1: MCPTT first-to-answer call response (MCPTT server to MCPTT client) information elements
|
Information Element |
Status |
Description |
|
MCPTT ID |
M |
The MCPTT ID of the calling party |
|
Functional alias |
O |
The functional alias of the calling party |
|
MCPTT ID |
M |
The MCPTT ID of the called party |
|
Functional alias |
O |
The functional alias of the called party |
|
SDP answer |
M |
Media parameters selected |
10.15.2.5 MCPTT first-to-answer call cancel request (MCPTT server to MCPTT client)
Table 10.15.2.5-1 describes the information flow MCPTT first-to-answer call cancel request from the MCPTT server to the MCPTT client.
Table 10.15.2.5-1: MCPTT first-to-answer call cancel request (MCPTT server to MCPTT client) information elements
|
Information Element |
Status |
Description |
|
MCPTT ID |
M |
The MCPTT ID of the calling party |
|
MCPTT ID |
M |
The MCPTT ID of the called party |
10.15.2.6 MCPTT first-to-answer call cancel response (MCPTT client to MCPTT server)
Table 10.15.2.6-1 describes the information flow MCPTT first-to-answer call cancel response from the MCPTT client to the MCPTT server.
Table 10.15.2.6-1: MCPTT first-to-answer call cancel response (MCPTT client to MCPTT server) information elements
|
Information Element |
Status |
Description |
|
MCPTT ID |
M |
The MCPTT ID of the called party |
10.15.3 Procedure
All clients are served by the primary MCPTT service provider in figure 10.15.3-1.
Pre-conditions:
1. The calling MCPTT user has selected first-to-answer call.
2. MCPTT clients 1 to n are registered and their respective users, MCPTT user 1 to MCPTT user n, are authenticated and authorized to use the MCPTT service, as per procedure in subclause 10.2.
3. MCPTT clients 2 to n have activated the same functional alias.
4. The MCPTT server has subscribed to the MCPTT functional alias controlling server within the MC system for functional alias activation/de-activation updates.
Figure 10.15.3-1: MCPTT first-to-answer call – MCPTT users in the same MCPTT system
1. MCPTT user at MCPTT client 1 would like to establish a MCPTT first-to-answer call indicating a set of potential target recipients or by calling a functional alias. For a MCPTT first-to-answer call with floor control, floor control is to be established. For first-to-answer call without floor control, both users will have the ability to transmit without floor arbitration.
2. MCPTT client 1 sends an MCPTT first-to-answer call request including a set of potential target recipients to the MCPTT server (via the SIP core as defined in 3GPP TS 23.228 [5]), using either a list of MCPTT IDs or a functional alias. The MCPTT first-to-answer call request contains the MCPTT ID and may contain the functional alias of originating user and an SDP offer containing one or more media types. The MCPTT first-to-answer call request may also contain a data element that indicates that MCPTT client 1 is requesting the floor, for a first-to-answer call with floor control. The MCPTT client 1 includes a first-to-answer call indication that the call is to be established only to the first answering user.
3. The MCPTT server confirms that MCPTT users are authorized for the call and whether the MCPTT user at MCPTT client 1 is authorized to initiate a first-to-answer call. The MCPTT server checks whether the provided functional alias of the calling user, if present, can be used and has been activated for the MCPTT user. If a functional alias is present, the MCPTT server shall also check whether MCPTT client 1 is allowed to use the functional alias of MCPTT client 2 (to MCPTT client n) to setup a private call and whether MCPTT client 2 (to MCPTT client n) is (are) allowed to receive a private call from MCPTT client 1 using a functional alias.
4. The MCPTT server determines the list of MCPTT users to send MCPTT first-to-answer call request, based on a set of potential target recipients obtained from the request from MCPTT client 1. Alternatively, when a functional alias is used as target address, the MCPTT server resolves the functional alias to a corresponding list of related MCPTT IDs of MCPTT client 2 to MCPTT client n who have activated the functional alias. The functional alias must have been activated to identify the MCPTT IDs of the called users.
Editor’s note: Whether the MCPTT server shall proceed only with those MCPTT IDs which are allowed to be called by MCPTT client 1 is FFS.
5a, 5b, 5c. The MCPTT server includes information that it communicates using MCPTT service, offers the same media types or a subset of the media types contained in the initial received request and sends similar MCPTT first-to-answer call request to each potential target recipient, including the MCPTT ID and, if present, the functional alias of the calling MCPTT user at MCPTT client 1. If one or more called MCPTT users have registered to the MCPTT service with multiple MCPTT UEs and has designated the MCPTT UE for receiving the calls, then the incoming MCPTT first-to-answer call request is delivered only to the designated MCPTT UE. Otherwise MCPTT first-to-answer call request may be delivered to all the registered MCPTT UEs. If a functional alias is present and more than one MCPTT client has activated that functional alias, then the MCPTT server sends an MCPTT first-to-answer call request to each MCPTT client.
6a, 6b, 6c. The MCPTT users are alerted, regardless of the commencement mode.
7. MCPTT user at MCPTT client 2 accepted the call which causes MCPTT client 2 to send an MCPTT first-to-answer call response to the MCPTT server.
NOTE 1: MCPTT server does not divert MCPTT first-to-answer call to voicemail if MCPTT user at MCPTT client 2 has not accepted the incoming call.
8. The MCPTT server sends an MCPTT first-to-answer call response to MCPTT client 1 indicating that MCPTT user at MCPTT client 2 has accepted the call, including the accepted media parameters.
9a. The MCPTT server sends a MCPTT first-to-answer call cancel request to MCPTT client 3.
9b. Optionally, MCPTT client 3 notifies the user.
10a. The MCPTT server sends a MCPTT first-to-answer call cancel request to MCPTT client n.
10b. Optionally, MCPTT client n notifies the user.
11. The media plane for communication is established. Either user can transmit media individually when using floor control. For successful call establishment for first-to-answer call with floor request from MCPTT client 1, the floor participant associated with MCPTT client 1 is granted the floor initially. At the same time the floor participant associated with MCPTT client 2 is informed that the floor is taken. For a first-to-answer call without floor control both users are allowed to transmit simultaneously.
NOTE 2: Prior to media plane establishment, MCPTT client 1 and MCPTT client 2 set up a security association for the media, if end-to-end encryption is used for this call.
Editor’s note: It is assumed that MCPTT client 1 initiates the set up as is done for private calls, but the details for the media security establishment are FFS and are in the scope of SA3. Results provided by SA3 may require changes in the procedure.
NOTE 3: The steps 9a ,10a and 11 can occur in any order and can also be performed in parallel.
12. MCPTT client 3 sends an MCPTT first-to-answer cancel call response.
13. MCPTT client n sends an MCPTT first-to-answer cancel call response.