Home media servers, AUPs, and upstream bandwidth utilization.

Tue Dec 26 17:07:10 UTC 2006

Chris mentioned:

#it might also be interesting to know how tcp-stack differences affect some
#of the usage patterns as well. With the now widely deployed win* platform
#tcp stach respecting tcp-reno things work according to well
#understood/accepted models. Mac OSX, linux and Vista seem to NOT respect
#tcp-reno, and may change the models somewhat... Will this cause more
#spikiness on individual links? will this change in behaviour on a wide
#scale (vista rollout to new computers or to existing platforms) causing
#folks capacity planning models to fail?

Capacity planning is a very important issue, but for other folks capacity
*under*utilization is the flip side of that issue. For example, there are 
still scientific researchers who continue to be puzzled by low throughput 
for bulk data transfers, even with clean fast ethernet (or gig ethernet!) 
connections end-to-end. For example, looking at table 1 of 

   http://netflow.internet2.edu/weekly/20061218/ 

we can see that on I2 95% of all bulk TCP data transfers are ~25Mbps or 
less -- however the top 1/10th of 1% successfully demonstrate 1Gbps 
throughput. 

The question then becomes one of "How do we help bridge that 'wizard
gap' or transfer that expertise (of those who are demonstrably able to 
fully utilize the connections at their disposal) to all the other 
well-connected researchers out there?" 

Things like Web100, see 

   http://www.web100.org/download/ 

are intended to help automate this for Linux users, although clearly 
there are still issues with applications (if you're curious, you 
can see the sort of improvements to SSH that were made by the folks 
at PSC at:

   http://www.psc.edu/networking/projects/hpn-ssh/ 

and there's a lot of fascinating empirical work that's been done with 
applications such as GridFTP (where encryption is not the bottleneck). 

So what about Vista? Well, it has (or should have, I'll withold any final
assertions until I see what actually finally gets shipped to consumers)
a number of TCP performance enhancements which are described at
http://www.microsoft.com/technet/community/columns/cableguy/cg1105.mspx
(last updated September 22nd, 2006). If the network traffic load feels 
different post-Vista, well, it very well may *be* different. :-)

But that's all host-based -- what about at the network level?

I'm intrigued to see things like jumbo frames accounting for a non-negligible 
fraction of traffic on Internet2 (e.g., roughly 7% or so of octets, see 
http://netflow.internet2.edu/weekly/longit/perc-b-jumbo-packets.png ),
and I also notice that at least one alternative TCP/IP implementation
has elected to commercialize in the form of a 1U gateway appliance that 
does its mojo network wide, rather than working to retrofit individual 
hosts with high performance TCP stacks on a host-by-host basis.

I think those sort of things have tremendous potential to change the
aggregate network behavior we all see over time.

Regards,

Joe St Sauver (joe at uoregon.edu)
http://www.uoregon.edu/~joe/
Disclaimer: all opinions strictly my own.