The WebSocket protocol enables two-way real-time communication between clients and servers in situations where direct access to TCP and UDP is not available (for example@ from within JavaScript in a web browser). This document specifies a new WebSocket subprotocol as a reliable transport mechanism between Message Session Relay Protocol (MSRP) clients and relays to enable usage of MSRP in new scenarios. This document normatively updates RFCs 4975 and 4976.