On Tue, Jul 31, 2001 at 12:15:58PM +0100, Jean-Christophe Varaillon wrote:
> So the time required to clock the data out should be like
>
> 80 bytes * 8 / 10^8 = 6.4 * 10^2 / 10^8 = 6.4 us
>
> Assume that the router copies the data each way, so the time required
> should be four copy times
>
> 4 * 6.4 us = 25.6 us = 0.025 ms
>
> plus delays at either end. Why is the delay so great?
Because it takes time for the BSD boxes to process the packets at each end then
send the packets to the network card for transmission. The RTT measured by ping
includes time spent in the local and remote IP stacks.
> * we are transmitting about 20 times as much data, but the
> ping time is only doubling
>
> * on the other hand, the time for four copies is going up by
> about 0.5 ms, but the time time is going up by around 2.5
> times as much
>
> Why is that?
Because some of the time taken in the IP stack is fixed (Amount of time it
takes to process the IP header, make routing decisions etc) regardless of the
packet size whereas other time is variable. (Such as the amount of time it
takes to copy the packet between different memory locations)
-- Ryan O'Connell - <ryan@complicity.co.uk> - http://www.complicity.co.ukI'm not losing my mind, no I'm not changing my lines, I'm just learning new things with the passage of time
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