# Messaging APIs The PortSIP Instant Messaging (IM) service facilitates the routing and storage of messages for both peer-to-peer and group communications, utilizing a publish-subscribe model. The core components of this service include sessions, users, and topics. * **Sessions**: These are WebSocket connections established between client applications and the server. * **Users**: PBX users (extensions) who connect to the IM service through active sessions. * **Topics**: Named communication channels that route content between sessions. Both peer-to-peer and group messaging operate within the framework of topics. Each user and topic within the IM service is assigned a unique identifier for seamless communication and message management. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://support.portsip.com/development-portsip/messaging-apis.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.