ASP.NET SignalR

SignalR is an Async signaling library for ASP.NET to help build real-time, multi-user interactive web applications. ASP.NET SignalR is a library for ASP.NET developers that makes it incredibly simple to add real-time web functionality to your applications. What we mean to say "real-time web" functionality? Real-time web is the ability to have your server-side code push content to the connected clients as it happens, in real-time.

HTML 5 introduces WebSockets which enables bi-directional communication between the browser and server. SignalR uses WebSockets under the cover when it is available and when WebSockets does not available, SignalR gracefully uses other techniques and technologies (i.e. Server-Sent Events, Forever Frame etc) while application code stays the same.

SignalR provides a very simple, high-level API which calls JavaScript functions in your clients' browsers from server-side .NET code in your ASP.NET application using Remote Procedure Calls (RPC), as well as adding useful hooks for connection management, e.g. connect/disconnect events, grouping connections, authorization.

A Connection represents a simple endpoint for sending single-recipient, grouped, or broadcast messages. SignalR handles connection management automatically, and lets you broadcast messages to all connected clients simultaneously, like a chat room. You can also send messages to specific clients. The connection between the client and server is persistent, unlike a classic HTTP connection, which is re-established for each communication.

The SignalR API contains two models for communicating between clients and servers:

·         Persistent Connections

·         Hubs.

The Persistent Connection API (represented in .NET code by the PersistentConnection class) gives the developer direct access to the low-level communication protocol that SignalR exposes. Using the Connections communication model will be familiar to developers who have used connection-based APIs such as Windows Communication Foundation.

A Hub is a more high-level pipeline built upon the Connection API that allows your client and server to call methods on each other directly. SignalR handles the dispatching across machine boundaries as if by magic, allowing clients to call methods on the server as easily as local methods, and vice versa. Using the Hubs communication model will be familiar to developers who have used remote invocation APIs such as .NET Remoting. Using a Hub also allows you to pass strongly typed parameters to methods, enabling model binding.

SignalR can be used to add any sort of real-time web functionality to your ASP.NET application. While chat is often used as an example, you can do a whole lot more. Any time a user refreshes a web page to see new data, or the page implements Ajax long polling to retrieve new data, is candidate for using SignalR. It also enables completely new types of applications, that require high frequency updates from the server, e.g. real-time gaming.

More about signalR, you may visit asp.com/signalR