My Understanding of HTTP Polling, Long Polling, HTTP Streaming and WebSockets

Question

I have read many posts on SO and the web regarding the keywords in my question title and learned a lot from them. Some of the questions I read are related to specific implem

Answer 1

There are more differences than the ones you have identified.

Duplex/directional:

• Uni-directional: HTTP poll, long poll, streaming.
• Bi-direcitonal: WebSockets, plugin networking

In order of increasing latency (approximate):

• WebSockets
• Plugin networking
• HTTP streaming
• HTTP long-poll
• HTTP polling

CORS (cross-origin support):

• WebSockets: yes
• Plugin networking: Flash via policy request (not sure about others)
• HTTP * (some recent support)

Native binary data (typed arrays, blobs):

• WebSockets: yes
• Plugin networking: not with Flash (requires URL encoding across ExternalInterface)
• HTTP *: recent proposal to enable binary type support

Bandwidth in decreasing efficiency:

• Plugin networking: Flash sockets are raw except for initial policy request
• WebSockets: connection setup handshake and a few bytes per frame
• HTTP streaming (re-use of server connection)
• HTTP long-poll: connection for every message
• HTTP poll: connection for every message + no data messages

Mobile device support:

• WebSocket: iOS 4.2 and up. Some Android via Flash emulation or using Firefox for Android or Google Chrome for Android which both provide native WebSocket support.
• Plugin networking: some Android. Not on iOS
• HTTP *: mostly yes

Javascript usage complexity (from simplest to most complicated). Admittedly complexity measures are somewhat subjective.

• WebSockets
• HTTP poll
• Plugin networking
• HTTP long poll, streaming

Also note that there is a W3C proposal for standardizing HTTP streaming called Server-Sent Events. It is currently fairly early in it's evolution and is designed to provide a standard Javascript API with comparable simplicity to WebSockets.