Ajax: poor resource utilization, because CPU-cycles and memory are needlessly allocated to prematurely or belatedly detect updates on the serverComet: lack of standard implementationdue the varying levels of support provided by browser vendors for XHR and iFramesEven in long-polling, HTTP Headers in the response outweigh the message being delivered
Desktop TCP (good performance)Request-Response (bad performance, poor bandwidth usage)Browser Polling, Long Polling, Streaming (limited real-time, proxy problems)Portals aggregating content at server (poor scalability)Mashupsaggregating at client for improved scalability – security problems
WebSocket is text-only
Authors, evangelists, and companies involved in the standardization still refer to the original set of features, including Web Sockets, as "HTML5."
HTTP used for handshake onlyOperates over a single socketTraverses firewalls and routers seamlesslyAllows authorized cross-site communicationCookie-based authenticationExisting HTTP load balancersNavigates proxies using HTTP CONNECT, same technique as https, but without the encryption