6 Protocol using SIP for session-mode messaging

24.2473GPPMessaging service using the IP Multimedia (IM) Core Network (CN) subsystemRelease 17Stage 3TS

6.1 Introduction

6.2 Functional entities

6.2.1 User Equipment (UE)

For the purpose of session-mode messaging, the UE shall implement the role of a Participant as described in clause 6.3.1.

6.3 Role

6.3.1 Participant

6.3.1.1 General

The participant shall perform SIP related session procedures in accordance with 3GPP TS 24.229 [5] to set up the dialog used for session-based messaging.

6.3.1.2 Session initiation – mobile originating case

When the originating participant wishes to engage the terminating participant in a session-mode message session, it shall use the call initiation procedure specified in 3GPP TS 24.229 [5]. The Request URI header shall include the URI of the terminating participant.

6.3.1.3 Session initiation – mobile terminating case

When the terminating participant receives an initial INVITE request from the originating endpoint proposing a message session, the terminating participant shall apply the procedures as specified in 3GPP TS 24.229 [5].

6.3.2 Intermediate Node

6.3.2.1 General

The intermediate node shall act as a Routeing B2BUA as specified in clause 5.7 in 3GPP TS 24.229 [5].

6.3.2.2 Generic procedures for all methods at the intermediate node

6.3.2.2.1 Intermediate node – originating case

The intermediate node shall follow the procedures of 3GPP TS 24.229 [5] clause 5.7.3 when acting as an originating UA.

6.3.2.2.2 Intermediate node – terminating case

Upon receipt of an initial request the intermediate node shall follow the procedures of 3GPP TS 24.229 [5] clause 5.7.1.2 in relation to the contents of the P-Charging-Function-Addresses header and the P-Charging-Vector header.

When creating the first response for this initial request, the intermediate node shall:

1) include the P-Charging-Vector header including:

a) the value of the icid parameter as received in the initial request;

b) the value of the orig-ioi parameter as received in the initial request; and

c) the term-ioi parameter, indicating the network of the intermediate node; and

2) include the P-Charging-Function-Addresses header as received in the initial request or, if the P-Charging-Function-Addresses header was not received in the initial request indicate the values applicable for the conference in the P-Charging-Function-Addresses header.

When creating responses for an initial INVITE request, the intermediate node shall additionally send the 200 (OK) response to the initial INVITE request only after the resource reservation has been completed.

6.3.2.3 Session Initiation

6.3.2.3.1 Session initiation – originating case

The intermediate node shall follow the procedures of 3GPP TS 24.229 [5] at call initiation.

The intermediate node shall populate the INVITE as specified for a Routeing B2BUA with the following clarification:

a) the Request URI to the URI as in the received Request URI:

b) the To header to the same display name and URI as in the received To header;

c) the From header sent includes the same display name and URI as in the From header in the received INVITE; and

d) the P-Asserted-Identity header and privacy includes the same information as in the received P-Asserted-Identity header and Privacy header; and

If the intermediate node is not able to establish a TCP connection for the MSRP session the intermediate node shall send BYE towards the participant and release the associated recourses.

6.3.2.3.2 Session initiation – terminating case

Upon receipt of an INVITE request that includes the terminating participant URI in the request URI, the intermediate node shall:

1) verify the identity of the user as described in clause 5.7.1.4 of 3GPP TS 24.229 [5] and authorize the request as described in clause 5.7.1.5 of 3GPP TS 24.229 [5]. The following actions in this clause shall only be performed if the request can be authorized;

2) establish the session in accordance with 3GPP TS 24.229 [5]; and

3) create a 200 (OK) response.