D.5 LI for chat

33.1273GPPLawful Interception (LI) architecture and functionsRelease 18TS

D.5.1 Background

The RCS 1-to-1 chat service and group chat service use SIP procedures for the setup of chat sessions and MSRP for the exchange of user messages as defined in RCC.07 [35] clause 3.2.3. Each MSRP SEND request containing a user message contains a request to receive a delivery notification and possibly a display notification. The client therefore always includes the header field for delivery notification when sending a message. The notifications may be delivered within the 1-to-1 chat session as MSRP SEND requests or outside the 1-to-1 chat session as a pager mode message delivery notification. Multimedia content is not permitted in user messages. Only text/plain user messages can be exchanged.

For the establishment of a group chat session, an RCS user selects at least 2 contacts capable of the chat service. Only ad-hoc groups are authorized. An ad-hoc group is a list of addresses created by the target dynamically. Pre-defined group are not permitted. Extending of a 1-to-1 chat to a group chat is not applicable for the current version of the RCS specification. Users may dynamically add additional participants to a group chat, if they are capable to support chat service.

D.5.2 Architecture

The figure 7.13.2-1 provides the architecture for LI for 1-to-1 chat.