Thank you for the information. One of these days I'll get ambitious and
buy a couple of gigabit cards.
Kurt Granroth wrote:
> Not much more, in any case. The general rule of thumb for a 100Mbps
> network is 40% efficiency.
>
> My knowledge of this is sporadic, rusty, and incomplete... but here goes:
>
> 100BaseT dictates that each 8 bit byte is encoded in a 10 bit packet.
> Therefore, the theoretical max throughput of raw bits would be about
> 76Mbps (megabit would be 1024x1204, not 1000x1000 when talking about data).
>
> Nobody pushes raw bits over the network, though. We use Ethernet on one
> layer and then IP and then TCP or UDP. All of these layers have their
> overhead. Let's take TCP/IP over Ethernet. A maximum Ethernet packet
> is 1514 bytes. Of that, 54 or 66 bytes (depending on data type) are
> taken by the Ethernet, IP, and TCP headers. That's about 4%. But then,
> TCP requires an ACK packet for each and every data packet. That means
> that the headers actually take up about 8% of the space. Subtracting
> that from our theoretical max shows that the TCP/IP over Ethernet has a
> theoretical max of 70Mbps.
>
> Remember, though, that up to now, we are talking about theoretical
> maximums. The real world is quite a bit more variable. Here's where my
> knowledge gets increasingly iffy. Take each statement from this point
> on with a big grain of salt.
>
> Okay, so the theoretical max is 70Mbps but that assumes that each packet
> is maxed out with data. If we go to a worst case scenario where each
> data packet only contains 1 byte, then the actual throughput would be
> less than 1Mbps. Say the packets are each (on average) half full.
> Then, our actual throughput would be under 60Mbps.
>
> Beyond this, I admit that it gets into voodoo territory. I know there
> are a lot of other factors (like packet switching, collisions, etc) that
> work to drive the actual throughput lower and lower but I don't know
> enough about those factors to really comment.
>
> The end result, though, is that 40% is the highest you can reasonably
> expect. So 33Mbps is getting pretty close. Maybe you could eek another
> 4 or 5Mbps out of that that with some careful tweaking... but that's
> going to be it.
>
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