Does HTTP use UDP?

Question

This might be a silly question:

• Does HTTP ever use the User Datagram Protocol?

For example:

If one is streaming MP3 or video using HTTP, does it internally use UDP for transport?

Answer 1

If you are streaming an mp3 or video that may not necessarily be over HTTP, in fact I'd be suprised if it was. It would probably be another protocol over TCP but I see no reason why you cannot stream over UDP.

If you do you have to take into account that there is no certainty that your data will arrive at the other end, but I can take it that you know about UDP.

To answer you question, No, HTTP does NOT use UDP. For what you talk about though, mp3/video streaming COULD happen over UDP and in my opinion should never happen over HTTP.

Answer 2

In theory yes it is possible to use UDP for http but that might be problematic. Say for instance in your example a mp3 or a video is being streamed there will be problem of ordering and some bits might go missing as UDP is not connection oriented there is no retransmit mechanism.

Answer 3

Of course, it doesn't necessarily have to be transmitted over TCP. I implemented HTTP on top of UDP, for use in the Satellite TV Broadcasting industry.

Answer 4

UDP is the best protocol for streaming, because it doesn't make demands for missing packages like TCP. And if it doesn't make demands, the flow is far more faster and without any buffering.

Even the stream delay is lesser than TCP. That is because TCP (as a far more secure protocol) makes demands for missing packages, overwriting the existing ones.

So TCP is a protocol too advanced to be used for streaming.

Answer 5

Typically, no.

Streaming is seldom used over HTTP itself, and HTTP is seldom run over UDP. See, however, RTP.

For something as your example (in the comment), you're not showing a protocol for the resource. If that protocol were to be HTTP, then I wouldn't call the access "streaming"; even if it in some sense of the word is since it's sending a (possibly large) resource serially over a network. Typically, the resource will be saved to local disk before being played back, so the network transfer is not what's usually meant by "streaming".

As commenters have pointed out, though, it's certainly possible to really stream over HTTP, and that's done by some.

Answer 6

From RFC 2616:

HTTP communication usually takes place over TCP/IP connections. The default port is TCP 80, but other ports can be used. This does not preclude HTTP from being implemented on top of any other protocol on the Internet, or on other networks. HTTP only presumes a reliable transport; any protocol that provides such guarantees can be used; the mapping of the HTTP/1.1 request and response structures onto the transport data units of the protocol in question is outside the scope of this specification.

So although it doesn't explicitly say so, UDP is not used because it is not a "reliable transport".

EDIT - more recently, the QUIC protocol (which is more strictly a pseudo-transport or a session layer protocol) does use UDP for carrying HTTP/2.0 traffic and much of Google's traffic already uses this protocol. It is not yet published as an RFC, though.