Intro Websocket enables a browser to be capable of synchronous communication using TCP Python/Java: Websocket / C#: signalR / nodejs: socket.io(long polling) [Traditional] Only when a browser sends a request -> A web server responses back to the request <- (asynchronous, unidirectional) [Websocket] After a connection is established between a browser and a webserver, whichever part can send messages any time via the connection (connection-oriented, bidirectional) included in HTML5 standards, supported by most browsers A simple websocket echo: a python server and an HTML client A Server in Python Prep.