ASP.NET Core SignalR is an open-source library that simplifies adding real-time web functionality to apps. Real-time web functionality enables server-side code to push content to clients instantly.
* Apps that require high frequency updates from the server. Examples are gaming, social networks, voting, auction, maps, and GPS apps.
* Dashboards and monitoring apps. Examples include company dashboards, instant sales updates, or travel alerts.
* Collaborative apps. Whiteboard apps and team meeting software are examples of collaborative apps.
* Apps that require notifications. Social networks, email, chat, games, travel alerts, and many other apps use notifications.
SignalR provides an API for creating server-to-client [remote procedure calls (RPC)](https://wikipedia.org/wiki/Remote_procedure_call). The RPCs call JavaScript functions on clients from server-side .NET Core code.
A hub is a high-level pipeline that allows a client and server to call methods on each other. SignalR handles the dispatching across machine boundaries automatically, allowing clients to call methods on the server and vice versa. You can pass strongly-typed parameters to methods, which enables model binding. SignalR provides two built-in hub protocols: a text protocol based on JSON and a binary protocol based on [MessagePack](https://msgpack.org/). MessagePack generally creates smaller messages compared to JSON. Older browsers must support [XHR level 2](https://caniuse.com/#feat=xhr2) to provide MessagePack protocol support.
Hubs call client-side code by sending messages that contain the name and parameters of the client-side method. Objects sent as method parameters are deserialized using the configured protocol. The client tries to match the name to a method in the client-side code. When the client finds a match, it calls the method and passes to it the deserialized parameter data.
