SIP may be used over websocket for web friendly environments and technologies. One example where this may be used is for the webrtc technology which is currently being standardized in W3C and IETF.
An IETF draft is being prepared at this point of time to standardize the usage of SIP over Websocket protocol.
At the same time Java EE 7 is standardizing a new API for websocket under JSR 356.
The goal of this feature is to standardize the usage of SIP Servlet API, when websocket is used as the transport for SIP.