Come to TEDMed -- SMART Letter #83 (fwd)

James Rogers
28 Jan 2003 11:45:02 -0800

Speaking of bits, it is time that hand-off "Mbits" went the way of "MHz"
as a meaningful metric of performance or utility.  There was a time
several years ago when all Mbits were roughly created equal, but that is
no longer the case.  Transport protocols and architecture have a huge
impact on realized performance.  TDM versus Ethernet?  Give yourself a
30% effective bandwidth penalty for TDM to calculate the Ethernet
bandwidth equivalent (never mind TDMs latency).  Is the network switched
or routed, and to what extent?  Fully switched networks scale much more
gracefully and respond better under high load than router-centric
networks.  A good rule of thumb is that you need twice the capacity on a
router-based network that you do on a fully switched network to have the
same scaling characteristics, so knowing what the architecture you are
connecting to looks like matters.

And then there is the difference between the aggregate speed of the
hand-offs in comparison to the aggregate throughput capacity of the
peering cross-connects.  Yes, you can sell 100-Mbit/s for $50 and make a
profit, but you can't sell 100-Mbit/s through the core for that price.

The question to ask is NOT how fast the pipe is to their router.  The
most important question is what percentage of that bandwidth is fully
realized at the core.  5-Mbps through the core (i.e. 100% realized) is
worth a lot more than 100-Mbps that only realizes 2% at the core. 
Incidentally, many people do not understand that when you buy a telco
Internet circuit (like a T1 or T3), the amount of bandwidth realized at
the core is typically in the range of 6-25%.  Unfortunately, most IT
managers don't know what questions to ask and so network companies
artificially inflate the hand-off Mbits to make it seem like their
connection is "faster" even if it has no practical impact on actual

Buying bandwidth was much easier when only telcos were selling pipes.


-James Rogers

On Tue, 2003-01-28 at 03:57, Eugen Leitl wrote:
> Quote of Note: Larry Lessig on the Price of Connectivity
>   "To repeat again, here in Japan, they are selling 100 
>    megabits per second for US$50/month, 12 mbs for $25." 
> Larry Lessig in his blog, January 4, 2002,