[K12OSN] gigabit

[Timothy Legge]

On Wed, 2005-01-05 at 10:28, David Trask wrote:
> "Support list for opensource software in schools." <k12osn at redhat.com> on
> Wednesday, January 05, 2005 at 9:09 AM +0000 wrote:
> >The clients don't benefit from anything beyond 100Mb. 
> 
> Why?  If the server has gigabit, the clients have gigabit, and the network
> is gigabit...why wouldn't the data be served at gigabit speed?  There are
> some gigabit cards that etherboot will work with (not sure about
> PXE)....I've always wanted to try the whole thing at gigabit speed...I
> have gigabit servers and backbone, but my clients are 100baseT....I'd love
> to see how much fast it'd be if it was gigabit through and through.

There are probably a couple of reasons.  

Many applications and servers aren't tuned to take advantage of the
higher bandwidth.  

If you have ever downloaded a kernel via tftp using gigabit speed you
might wonder why it takes so long.  Even though many gigabit cards can
support much larger packets, typically packets are 512 in size.  That
means that there are still kernel_size/512 packets and an equivalent
number of acks.  That means that your bottle neck is no longer the
network but the speed of the tftp server and etherboot driver.  The same
would probably be true for nfs and X.

There is only so much data.  As some one pointed out, 100 Mbs is
sufficient for most thin clients.  The user only reacts so quickly and
is probably the bottle neck.  I have watched dvds on an Xterminal and
the quality was excellent.  Again, there was only so much data being
sent to my terminal.  On a busy network it would be slower but I only
needed a 100 mbs NIC.  Its like hooking fire hose to your outdoor water
outlet.  You probably won't fill a bucket any faster because there is
only so much water pressure.

As I see it, you remove the network as the bottleneck and you are then
limited by the slower of the user or the application/server that you are
using.

I could be way off base on this, its based on my limited (and often
incorrect) understanding of network cards and protocols.

Tim