[tjgq]

> Which assumptions? Using multiple connections is pretty standard in the enterprise storage world.

TCP congestion control is designed such that, under steady-state conditions, each TCP stream traversing a physical link gets an equal share of the available bandwidth. When an application that uses multiple TCP connections competes with another that uses a single one over the same link, the resulting bandwidth distribution is unfair to the latter. (Edit: there's also another problem, related to bufferbloat, but that one is a lot trickier to explain).

Of course, this may not be a problem when used on an internal network (which I assume is the scenario you are referring to). On the public Internet, however, HTTP is becoming increasingly disruptive to other kinds of traffic due to the increasing number of parallel connections used by web browsers.

[colanderman]

Ah yes. I'd say that's more a problem with TCP in general than in using multiple connections. The assumption that "1 TCP connection == 1 share of bandwidth" is at best a useful first approximation. I don't know that N TCP streams eating N times their "fair share" is really any different a problem than some-important-interactive-application being given equal bandwidth with some-irrelevant-background-download. (Though it might be a worse problem.)

I'd love to live to see the day that something actually better than TCP (that addresses these and other issues) dethrones it, but given how long IPv6 took to gain traction, I wouldn't be surprised if it didn't happen in my lifetime.

[tjgq]

I think it's a wonderful thing that the TCP/IP model (as originally envisioned) does not preclude endpoints from implementing their own transport protocols on top of IP, irrespective of what the rest of the network uses.

Unfortunately, reality has conspired against this possibility in two ways: NAT boxes, and the fact that transport protocols are implemented in the kernel on most operating systems (hence, an application cannot use its own transport protocol easily).

The deployment of IPv6 is a real chance to, at least, fix the first of these problems. Let's hope it does.