10.7.5 MCPTT call forwarding for private calls

23.3793GPPFunctional architecture and information flows to support Mission Critical Push To Talk (MCPTT)Release 18Stage 2TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

10.7.5.1 General

Call forwarding of MCPTT private calls allows users to configure forwarding of incoming private calls (with or without Floor control) to another MCPTT user depending on the following conditions:

– Immediate

– No answer: If the incoming private call is a call with manual commencement mode and the MCPTT User does not answer within a configured period

The forwarding of an individual call can also be based on manual input of the called MCPTT user on a per call basis. In this case the MCPTT user responds to an incoming MCPTT private call by requesting redirection of that MCPTT private call to another MCPTT user. It can only be invoked before the communication is established by the served user, which is the period that the served user is being informed of the communication (during ringing).

10.7.5.1.1 Void

10.7.5.1.2 MCPTT private call forwarding request (MCPTT client to MCPTT server and MCPTT server to MCPTT server)

Table 10.7.5.1.2-1 describes the information flow of the MCPTT private call forwarding request from the MCPTT client to the MCPTT server and MCPTT server to MCPTT server.

Table 10.7.5.1.2-1: MCPTT private call forwarding request (MCPTT client to MCPTT server and MCPTT server to MCPTT server) information elements

Information Element	Status	Description
MCPTT ID	M	The MCPTT ID requesting the call forwarding
MCPTT ID	M	The MCPTT ID originating the MCPTT private call
MCPTT ID (see NOTE)	O	The target MCPTT ID of the call forwarding
Functional alias (see NOTE)	O	The target functional alias of the call forwarding
NOTE: One identity shall be present

10.7.5.1.3 MCPTT private call forwarding response (MCPTT server to MCPTT client)

Table 10.7.5.1.3-1 describes the information flow of the MCPTT private call forwarding response from the MCPTT server to the MCPTT client.

Table 10.7.5.1.3-1: MCPTT private call forwarding response (MCPTT server to MCPTT client) information elements

Information Element	Status	Description
MCPTT ID	M	The MCPTT ID requesting the call call forwarding
Result	M	Result of the call forwarding request – success or fail

10.7.5.1.4 MCPTT private call forwarding request (MCPTT server to MCPTT client)

Table 10.7.5.1.4-1 describes the information flow of the MCPTT private call forwarding request from the MCPTT server to the MCPTT client.

Table 10.7.5.1.4-1: MCPTT private call forwarding request (MCPTT server to MCPTT client) information elements

Information Element	Status	Description
MCPTT ID	M	The MCPTT ID of the party to be forwarded
MCPTT ID	M	The target MCPTT ID of the call forwarding

10.7.5.1.5 MCPTT private call forwarding response (MCPTT client to MCPTT server and MCPTT server to MCPTT server)

Table 10.7.5.1.5-1 describes the information flow of the MCPTT private call forwarding response from the MCPTT client to the MCPTT server and MCPTT server to MCPTT server.

Table 10.7.5.1.5-1: MCPTT private call forwarding response (MCPTT client to MCPTT server and MCPTT server to MCPTT server) information elements

Information Element	Status	Description
MCPTT ID	M	The MCPTT ID of the party to be forwarded
MCPTT ID	M	The MCPTT ID of the target of the forwarding
Result	M	Result of the call forwarding request – success or fail

10.7.5.2 Procedures

10.7.5.2.1 Update configuration for MCPTT private call forwarding

An authorized user can update the call forwarding related parameters stored in the user profile using the procedures as defined in 3GPP TS 23.280 [8] subclause 10.1.4.5.

10.7.5.2.2 MCPTT immediate private call forwarding in a single MCPTT system

Figure 10.7.5.2.2-1 below illustrates the procedure of immediate call forwarding of MCPTT private calls.

Pre-conditions:

1. MCPTT client 2 is authorized to use call forwarding and has immediate call forwarding enabled with the destination MCPTT client 3.

2. MCPTT client 1 is authorized to make private calls to client 2.

3. The redirection counter is below the limit.

4. MCPTT client 1 has the necessary security information to initiate a private call with MCPTT client 2 and MCPTT client 3 if end2end encryption is required for the private call.

Figure 10.7.5.2.2-1: Call forwarding immediate for private calls

1. MCPTT client 1 sends an MCPTT private call request towards the MCPTT server.

2. The MCPTT server detects that MCPTT client 2 has immediate call forwarding enabled.

3. The MCPTT server checks that the limit of immediate forwardings is not reached. The MCPTT server increments the redirection counter for immediate forwardings. If the target of the MCPTT private call forwarding is a functional alias instead of an MCPTT ID the MCPTT server resolves the functional alias to the corresponding MCPTT ID for which the functional alias is active.

NOTE 1: Depending on implementation the MCPTT server can apply additional call restrictions and decide whether the call is allowed to proceed with the resolved MCPTT ID(s) (e.g. whether the MCPTT ID is within the allowed area of the functional alias). If the MCPTT server detects that the functional alias used as the target of the MCPTT private call forwarding is simultaneously active for multiple MCPTT users, then the MCPTT server can proceed by selecting an appropriate MCPTT ID based on some selection criteria. The selection of an appropriate MCPTT ID is left to implementation. The selection criteria can include rejection of the call, if no suitable MCPTT ID is selected.

3a. If the target of the call forwarding is a functional alias that is not active, or if the target functional is simultaneously active by multiple users and the outcome of the selection is a rejection, the MCPTT private call forwarding is cancelled, and the MCPTT server sends an MCPTT private call cancel request towards MCPTT client 1. Otherwise, the procedure continues with step 4.

3b. MCPTT client 1 sends an MCPTT call private cancel response back to the MCPTT server, and the procedure ends.

4. The MCPTT server sends an MCPTT private call forwarding request towards MCPTT client 1.

NOTE 2: The target MCPTT ID is based on the entry in the user profile for call forwarding immediate.

5. The user at MCPTT client 1 is notified that a call forwarding is in process.

6. MCPTT client 1 sends an MCPTT call private forwarding response back to the MCPTT server.

7. MCPTT client 1 sends an MCPTT private call request towards the MCPTT server that includes a call forwarding indication set to true. MCPTT client 1 and MCPTT client 3 set up a security association if end-to-end encryption is used for this call.

8. The MCPTT server verifies that client 1 is authorized to perform the MCPTT private call as a result of the MCPTT private call forwarding request. The MCPTT server verifies that the MCPTT private call request contains MCPTT client 3 that is the authorized target from step 4, and the forwarding indication is set to true.

9. The MCPTT server sends an MCPTT private call request towards MCPTT client 3.

10. Optionally the MCPTT server sends an MCPTT progress indication to MCPTT client 1.

11. The user at MCPTT client 3 is alerted. MCPTT client 3 sends an MCPTT ringing to the MCPTT server. This step is not required in case of automatic commencement mode.

12. The MCPTT server sends an MCPTT ringing to MCPTT client 1. This step is not required in case of automatic commencement mode.

13. MCPTT client 3 sends an MCPTT private call response to the MCPTT server. In manual commencement mode this occurs after the user at MCPTT client 3 has accepted the call.

14. The MCPTT server sends an MCPTT private call response to MCPTT client 1 indicating that MCPTT client 3 has accepted the call.

15. The media plane for communication between MCPTT client 1 and MCPTT client 3 is established.

10.7.5.2.3 MCPTT private call forwarding no answer in a single MCPTT system

Figure 10.7.5.2.3-1 below illustrates the procedure of call forwarding no answer of MCPTT private calls.

NOTE 1: The condition no answer covers both the cases in which the user does not answer because he is not reachable, as well as the case in which he is reachable but does not answer.

Pre-conditions:

1. MCPTT client 2 is authorized to use call forwarding and has call forwarding no answer enabled with the destination MCPTT client 3.

2. MCPTT client 1 is authorized to make private calls to MCPTT client 2.

3. No forwarding with no answer or based on manual user input has so far occurred in this call.

4. MCPTT client 1 has the necessary security information to initiate a private call with MCPTT client 2 and MCPTT client 3 if end2end encryption is required for the private call.

Figure 10.7.5.2.3-1: MCPTT call forwarding no answer

1. MCPTT client 1 sends an MCPTT private call request towards the MCPTT server.

2. The MCPTT server checks if MCPTT client 2 has call forwarding no answer enabled. If the MCPTT server detects that MCPTT client 2 is not registered, the procedure continues with step 7. Otherwise, the MCPTT server starts a timer with the configured no answer timeout.

3. The MCPTT server sends an MCPTT private call request in manual commencement mode towards MCPTT client 2. If the MCPTT server detects that MCPTT client 2 is not reachable, the procedure continues with step 7.

4. The user at MCPTT client 2 is alerted. MCPTT client 2 sends an MCPTT ringing to the MCPTT server.

5. The MCPTT server sends an MCPTT ringing to the MCPTT client 1. This step is not required in case of automatic commencement mode.

6. The MCPTT server detects that MCPTT client 2 does not answer within the specified time interval.

7. The MCPTT server verifies that no other forwarding with the condition no answer or based on manual user input has occurred so far. If the target of the MCPTT private call forwarding is a functional alias instead of an MCPTT ID the MCPTT server resolves the functional alias to the corresponding MCPTT ID for which the functional alias is active.

NOTE 2: Depending on implementation the MCPTT server can apply additional call restrictions and decide whether the call is allowed to proceed with the resolved MCPTT ID(s) (e.g. whether the MCPTT ID is within the allowed area of the functional alias). If the MCPTT server detects that the functional alias used as the target of the MCPTT private call forwarding is simultaneously active for multiple MCPTT users, then the MCPTT server can proceed by selecting an appropriate MCPTT ID based on some selection criteria. The selection of an appropriate MCPTT ID is left to implementation. The selection criteria can include rejection of the call, if no suitable MCPTT ID is selected.

7a. If the target of the call forwarding is a functional alias that is not active, or if the target functional is simultaneously active by multiple users and the outcome of the selection is a rejection, the MCPTT private call forwarding is cancelled, and the MCPTT server sends an MCPTT private call cancel request towards MCPTT client 1. Otherwise, the procedure continues with step 8.

7b. MCPTT client 1 sends an MCPTT call private cancel response back to the MCPTT server, and the procedure ends.

8. The MCPTT server sends an MCPTT private call forwarding request towards the MCPTT client 1.

NOTE 3: The target MCPTT ID is based on the entry in the user profile for call forwarding no answer.

9. The user at MCPTT client 1 is notified that a call forwarding is in process.

10. MCPTT client 1 sends an MCPTT private call forwarding response back to the MCPTT server.

11. MCPTT client 1 sends an MCPTT private call request towards the MCPTT server that includes a call forwarding indication set to true. MCPTT client 1 and MCPTT client 3 set up a security association if end-to-end encryption is used for this call.

12. The MCPTT server verifies that client 1 is authorized to perform the MCPTT private call as a result of the MCPTT private call forwarding request. The MCPTT server verifies that the MCPTT private call request contains MCPTT client 3 that is the authorized target from step 8, and the forwarding indication is set to true.

NOTE 4: For call forwarding the MCPTT server does not check if the initial originating MCPTT user at MCPTT client 1 is authorized to make an MCPTT private call to the final target MCPTT user at MCPTT client 3.

13. The MCPTT server sends an MCPTT private call request towards MCPTT client 3.

14. Optionally the MCPTT server sends an MCPTT progress indication to MCPTT client 1.

15. The user at MCPTT client 3 is alerted. MCPTT client 3 sends an MCPTT ringing to the MCPTT server. This step is not required in case of automatic commencement mode.

16. The MCPTT server sends an MCPTT ringing to MCPTT client 1. This step is not required in case of automatic commencement mode.

17. MCPTT client 3 sends an MCPTT private call response to the MCPTT server. In manual commencement mode this occurs after the user at MCPTT client 3 has accepted the call.

18. The MCPTT server sends an MCPTT private call response to MCPTT client 1 indicating that MCPTT client 3 has accepted the call.

19. The media plane for communication between MCPTT client 1 and MCPTT client 3 is established.

10.7.5.2.3a MCPTT private call forwarding based on manual user input in a single MCPTT system

Figure 10.7.5.2.3a-1 below illustrates the procedure of call forwarding based on manual user input of MCPTT private calls.

Pre-conditions:

1. MCPTT client 2 is authorized to perform call forwarding based on manual input.

2. MCPTT client 1 is authorized to make private calls to MCPTT client 2.

3. No forwarding with no answer or based on manual user input has so far occurred in this call.

4. MCPTT client 1 has the necessary security information to initiate a private call with MCPTT client 2 and MCPTT client 3 if end2end encryption is required for the private call.

Figure 10.7.5.2.3a-1: MCPTT call forwarding based on manual user input

1. MCPTT client 1 sends an MCPTT private call request towards the MCPTT server.

2. The MCPTT server checks if MCPTT client 2 has call forwarding no answer enabled. If the MCPTT server detects that MCPTT client 2 is not registered, the procedure continues with step 10. Otherwise, the MCPTT server starts a timer with the configured no answer timeout.

4. The user at MCPTT client 2 is alerted. MCPTT client 2 sends an MCPTT ringing to the MCPTT server.

5. In manual commencement mode the MCPTT server sends an MCPTT ringing to the MCPTT client 1.

6. During ringing the user at MCPTT client 2 requests the call to be forwarded based on manual input.

7. MCPTT client 2 sends an MCPTT private call forwarding request to the MCPTT server.

8. The MCPTT server verifies if the user at client 2 is allowed to perform forwarding based on manual input. If the target of the MCPTT private call forwarding is a functional alias instead of an MCPTT ID the MCPTT server resolves the functional alias to the corresponding MCPTT ID for which the functional alias is active.

8a. If the target of the call forwarding is a functional alias that is not active, or if the target functional is simultaneously active by multiple users and the outcome of the selection is a rejection, the MCPTT private call forwarding is cancelled, and the MCPTT server sends an MCPTT private call cancel request towards MCPTT client 1. Otherwise, the procedure continues with step 9.

8b. MCPTT client 1 sends an MCPTT call private cancel response back to the MCPTT server.

8c. The MCPTT server sends an MCPTT private call forwarding response with Result equals "fail" to MCPTT client 2, and the procedure ends.

9. The MCPTT server stops the timer for the no answer timeout.

10. The MCPTT server verifies that no other forwarding with the condition no answer or based on manual user input has occurred so far.

11.The MCPTT server sends an MCPTT private call forwarding response to MCPTT client 2.

12. The MCPTT server sends an MCPTT private call forwarding request towards the MCPTT client 1.

NOTE 2: The target MCPTT ID is based on the identity manually entered by the user at MCPTT client 2 in step 6.

13. The user at MCPTT client 1 is notified that a call forwarding is in process.

14. MCPTT client 1 sends an MCPTT private call forwarding response back to the MCPTT server.

15. MCPTT client 1 sends an MCPTT private call request towards the MCPTT server that includes a call forwarding indication set to true. MCPTT client 1 and MCPTT client 3 set up a security association if end-to-end encryption is used for this call.

16. The MCPTT server verifies that client 1 is authorized to perform the MCPTT private call as a result of the MCPTT private call forwarding request. The MCPTT server verifies that the MCPTT private call request contains MCPTT client 3 that is the authorized target from step 12, and the forwarding indication is set to true.

NOTE 3: For call forwarding the MCPTT server does not check if the initial originating MCPTT user at MCPTT client 1 is authorized to make an MCPTT private call to the final target MCPTT user at MCPTT client 3.

17. The MCPTT server sends an MCPTT private call request towards MCPTT client 3.

18. Optionally the MCPTT server sends an MCPTT progress indication to MCPTT client 1.

19. The user at MCPTT client 3 is alerted. MCPTT client 3 sends an MCPTT ringing to the MCPTT server. This step is not required in case of automatic commencement mode.

20. The MCPTT server sends an MCPTT ringing to MCPTT client 1. This step is not required in case of automatic commencement mode.

21. MCPTT client 3 sends an MCPTT private call response to the MCPTT server. In manual commencement mode this occurs after the user at MCPTT client 3 has accepted the call.

22. The MCPTT server sends an MCPTT private call response to MCPTT client 1 indicating that MCPTT client 3 has accepted the call.

23. The media plane for communication between MCPTT client 1 and MCPTT client 3 is established.

10.7.5.2.4 Handling of multiple MCPTT private call forwardings

If the target of the MCPTT private call forwarding has also any kind of MCPTT call forwarding activated generally the additional forwardings are performed sequentially. However, to avoid excessive numbers of forwardings and in particular to avoid indefinite loops in the forwarding a limit for immediate forwardings is defined in the service configuration. The MCPTT server keeps track of the number of forwardings, if the limit is exceeded, the call will be released. For forwarding no answer or for forwarding based on manual user input, only one forwarding is allowed, and in case of no answer on the first forwarding the MCPTT server will release the call.

10.7.5.2.5 MCPTT private call forwarding with target of the MCPTT private call forwarding in partner MCPTT system

The procedure describes the case for MCPTT for private call forwarding that an MCPTT user in a partner MCPTT system is the target of the MCPTT private call forwarding.

NOTE 1: The procedure shows manual commencement mode, but the changes are also applicable when using automatic commencement mode.

NOTE 2: The procedure focusses on the interaction between the MCPTT servers, which is independent of the condition of the call forwarding. Therefore, the procedure is generically applicable for all types of MCPTT private call forwarding.

Pre-conditions:

1. MCPTT client 2 is authorized to use call forwarding and has immediate call forwarding enabled with the destination MCPTT client 3.

2. MCPTT client 1 is authorized to make private calls to MCPTT client 2.

3. The redirection counter is below the limit.

4. MCPTT client 1 has the necessary security information to initiate a private call with MCPTT client 2 and MCPTT client 3 if end-to-end encryption is required for the private call.

Figure 10.7.5.2.5-1: Simplified private call setup with MCPTT private calls forwarding in manual commencement mode with forwarding target in the partner MCPTT system

1. MCPTT client 1 sends an MCPTT private call request towards MCPTT server 1.

1a If the MCPTT private call request contains a functional alias instead of an MCPTT ID as called party, MCPTT server 1 checks whether MCPTT client 1 is allowed to use the functional alias of MCPTT client 2 to setup a private call and whether MCPTT client 2 is allowed to receive a private call from MCPTT client 1 using the functional alias.

NOTE 1: If the target of the MCPTT private call request is a functional alias, the procedure resolves the functional alias to the corresponding MCPTT ID for which the functional alias is active. For simplicity details are not described in this procedure.

2. MCPTT server 1 detects that MCPTT client 2 has immediate call forwarding enabled to MCPTT client 3 which is registered in MCPTT system 2.

3. MCPTT server 1 sends an MCPTT private call forwarding request towards MCPTT client 1.

NOTE 2: If the target of the MCPTT private call forwarding is a functional alias, the procedure resolves the functional alias to the corresponding MCPTT ID for which the functional alias is active. For simplicity details of the resolution are not described.

4. The user at MCPTT client 1 is notified that a call forwarding is in process.

5. MCPTT client 1 sends an MCPTT call private forwarding response back to MCPTT server 1.

6. MCPTT client 1 sends an MCPTT private call request towards MCPTT server 1 that includes a call forwarding indication set to true.

7. MCPTT server 1 verifies that MCPTT client 1 is authorized to perform an MCPTT private call as a result of the MCPTT private call forwarding request. MCPTT server 1 verifies that the MCPTT private call request contains MCPTT client 3 that is the authorized target from step 3, and the forwarding indication is set to true.

8. MCPTT server 1 sends an MCPTT private call request towards MCPTT server 2.

9. MCPTT server 2 sends an MCPTT private call request towards MCPTT client 3.

NOTE 3: MCPTT server 2 detects that the private call request contains a forwarding indication is set to true and therefore skips the authorization checking.

10. Optionally MCPTT server 1 sends an MCPTT progress indication to MCPTT client 1.

11. The user at MCPTT client 3 is alerted. MCPTT client 3 sends an MCPTT ringing to MCPTT server 2. This step is not required in case of automatic commencement mode.

12. MCPTT server 2 sends an MCPTT ringing to MCPTT server 1. This step is not required in case of automatic commencement mode.

13. MCPTT server 1 sends an MCPTT ringing to MCPTT client 1. This step is not required in case of automatic commencement mode.

14. MCPTT client 3 sends an MCPTT private call response to MCPTT server 2. In manual commencement mode this occurs after the user at MCPTT client 3 has accepted the call.

15. MCPTT server 2 sends an MCPTT private call response to MCPTT server 1. In manual commencement mode this occurs after the user at MCPTT client 3 has accepted the call.

16. MCPTT server 1 sends an MCPTT private call response to MCPTT client 1 indicating that MCPTT client 3 has accepted the call.

17. The media plane for communication between MCPTT client 1 and MCPTT client 3 is established.

10.7.5.2.6 MCPTT private call forwarding with MCPTT private call forwarding occurring in the partner MCPTT system

The procedure for MCPTT private call forwarding describes the case of an MCPTT private call forwarding occurring in the partner MCPTT system.

NOTE 1: The procedure shows manual commencement mode, but the changes are also applicable when using automatic commencement mode.

NOTE 2: The procedure focusses on the interaction between the MCPTT servers, which is independent of the condition for the call forwarding. Therefore, the procedure is generically applicable for all types of call forwarding.

Pre-conditions:

1. MCPTT client 3 is authorized to use call forwarding and has immediate call forwarding enabled with the destination MCPTT client 2.

2. MCPTT client 1 is authorized to make private calls to MCPTT client 3.

3. The redirection counter is below the limit.

4. MCPTT client 1 has the necessary security information to initiate a private call with MCPTT client 2 and MCPTT client 3 if end-to-end encryption is required for the private call.

Figure 10.7.5.2.6-1: Simplified private call setup with MCPTT private calls forwarding in manual commencement mode with forwarding in the partner MCPTT systems

1. MCPTT client 1 sends an MCPTT private call request towards MCPTT server 1 for establishing an MCPTT private call with MCPTT client 3 registered at MCPTT system 2.

1a If the MCPTT private call request contains a functional alias instead of an MCPTT ID as called party, MCPTT server 1 checks checks whether MCPTT client 1 is allowed to use the functional alias of MCPTT client 3 to setup a private call.

2. MCPTT server 1 sends an MCPTT private call request towards MCPTT server 2 for establishing an MCPTT private call with MCPTT client 3 registered at MCPTT system 2.

2a If the MCPTT private call request contains a functional alias instead of an MCPTT ID as called party, MCPTT server 2 checks whether MCPTT client 3 is allowed to receive a private call from MCPTT client 1 using the functional alias.

3. MCPTT server 2 detects that MCPTT client 3 has immediate call forwarding enabled to MCPTT client 2 registered at MCPTT system 1.

4. MCPTT server 2 sends an MCPTT private call forwarding request towards MCPTT server 1.

5. MCPTT server 1 sends an MCPTT private call forwarding request towards MCPTT client 1.

6. The user at MCPTT client 1 is notified that a call forwarding is in process.

7. MCPTT client 1 sends an MCPTT call private forwarding response back to MCPTT server 1.

8. MCPTT server 1 sends an MCPTT call private forwarding response back to MCPTT server 2.

9. MCPTT client 1 sends an MCPTT private call request towards MCPTT server 1 that includes a call forwarding indication set to true.

10. MCPTT server 1 verifies that MCPTT client 1 is authorized to perform the MCPTT private call as a result of the MCPTT private call forwarding request. MCPTT server 1 verifies that the MCPTT private call request contains MCPTT client 2 that is the authorized target from step 5, and the forwarding indication is set to true.

11. MCPTT server 1 sends an MCPTT private call request towards MCPTT client 2.

12. Optionally MCPTT server 1 sends an MCPTT progress indication to MCPTT client 1.

13. The user at MCPTT client 2 is alerted. MCPTT client 2 sends an MCPTT ringing to MCPTT server 1. This step is not required in case of automatic commencement mode.

14. MCPTT server 1 sends an MCPTT ringing to MCPTT client 1. This step is not required in case of automatic commencement mode.

15. MCPTT client 2 sends an MCPTT private call response to MCPTT server 1. In manual commencement mode this occurs after the user at MCPTT client 2 has accepted the call.

16. MCPTT server 1 sends an MCPTT private call response to MCPTT client 1 indicating that MCPTT client 2 has accepted the call.

17. The media plane for communication between MCPTT client 1 and MCPTT client 2 is established.