[Gllug] Calculating 'real' bandwidth

[Russell Howe]

On Thu, Mar 15, 2007 at 12:57:02AM +0000, Pete Ryland wrote:
> On 15/03/07, Russell Howe <rhowe at siksai.co.uk> wrote:
> >Well, we know how big an ACK is, and we know how many packets per second
> >need ACKing (585), so it's easy - 106 * 585 = 62010 bytes/s of ACKs,
> >which is 496,080 bits/s
> >
> >Yep, that's right, 500Kbit/s of upstream is taken just ACKing your
> >downstream TCP traffic if you're going at full pelt!
> >
> >If you were running optimally, it's slightly worse - at 610 TCP packets
> >per second, that's 64,660 bytes/s or 517,280 bits/s of upstream
> >bandwidth taken up by TCP ACKs
> 
> It's been over 10 years since I last looked closely at this, but as
> far as I can recall, I thought the way sliding window worked allowed
> you to ACK more than one packet at the same time, that is, an ACK-n
> says "I've seen everything up to n."

Quite possibly. I couldn't remember if sequence numbers were sequential
or not, but I suppose it would be a rather poor choice of nomenclature
if they weren't :)

In that case, things aren't as bad as they at first seemed

-- 
Russell Howe       | Why be just another cog in the machine,
rhowe at siksai.co.uk | when you can be the spanner in the works?
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