Andrew Ducker (andrewducker) wrote,
Andrew Ducker

A quick question about TCP/IP

I was reading about TCP, congestion, etc. because of some presentation slides (which I wish I had the notes for, because I'd like the explanations that go with some of them.

And I realised that there was an inefficiency I was seeing. And the reason may be historical, or (entirely likely) something I'm just overlooking.

Why does _every_ packet requires an acknowledgement packet? Chances are that most packets are travelling as part of a set of packets - probably the maximum possible for the window size. So rather than taking up bandwidth sending back a load of them, why not delay a trivial amount of time after the first packet arrives and then acknowledge the highest number for which you have all of the previous packets?

You wouldn't want to delay long - but then you shouldn't need to - you'd generally expect that the next n packets would be arriving immediately behind each other, so acknowledging only only once every n milliseconds should work pretty effectively.

So if packets 2-6 arrive, send an ACK saying "*6" (or some equivalent signal), rather than five separate acks? I know ACK packets are tiny, but it still seems wasteful.

Anyone who's knowledgable in the area care to fill me in?

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