Cloudflare Docs
Calls
Cloudflare Docs
Calls
    GitHub icon
    Edit this page on GitHub
    Set theme to dark (⇧+D)
    1. Products
    2. Calls
    3. Sessions and Tracks

    Understanding Sessions and Tracks in Cloudflare Calls

    Cloudflare Calls offers a simple yet powerful framework for building real-time experiences. At the core of this system are two key concepts: Sessions and Tracks. Familiarizing yourself with these concepts is crucial for using Calls.

    ​​ Sessions

    A Session in Cloudflare Calls correlates directly to a WebRTC PeerConnection. It represents the establishment of a communication channel between a client and the nearest Cloudflare data center, as determined by Cloudflare’s anycast routing. Typically, a client will maintain a single Session, encompassing all communications between the client and Cloudflare.

    • One-to-One Mapping with PeerConnection: Each Session is a direct representation of a WebRTC PeerConnection, facilitating real-time media data transfer.
    • Anycast Routing: The client connects to the closest Cloudflare data center, optimizing latency and performance.
    • Unified Communication Channel: A single Session can handle all types of communication between a client and Cloudflare, ensuring streamlined data flow.

    ​​ Tracks

    Within a Session, there can be one or more Tracks.

    • Tracks map to MediaStreamTrack: Tracks align with the MediaStreamTrack concept, facilitating audio, video, or data transmission.
    • Globally Unique Ids: When you push a track to Cloudflare, it is assigned a unique ID, which can then be used to pull the track into another session elsewhere.
    • Available globally: The ability to push and pull tracks is central to what makes Calls a versatile tool for real-time applications. Each track is available globally to be retrieved from any Session within an App.

    ​​ Calls as a Programmable “Switchboard”

    The analogy of a switchboard is apt for understanding Calls. Historically, switchboard operators connected calls by manually plugging in jacks. Similarly, Calls allows for the dynamic routing of media streams, acting as a programmable switchboard for modern real-time communication.

    ​​ Beyond “Rooms”, “Users”, “Participants”

    While many SFUs utilize concepts like “rooms” to manage media streams among users, this approach has scalability and flexibility limitations. Cloudflare Calls opts for a more granular and flexible model with Sessions and Tracks, enabling a wide range of use cases:

    • Large-scale remote events, like ‘fireside chats’ with thousands of participants.
    • Interactive conversations with the ability to bring audience members “on stage.”
    • Educational applications where an instructor can present to multiple virtual classrooms simultaneously.

    ​​ Presence Protocol vs. Media Flow

    Calls distinguishes between the presence protocol and media flow, allowing for scalability and flexibility in real-time applications. This separation enables developers to craft tailored experiences, from intimate calls to massive, low-latency broadcasts.