>Date: Fri, 16 Mar 2001 22:35:02 -0500
>From: Joshua Wright <[log in to unmask]>
>Subject: [P2P] How much bandwidth is reasonable?
>To: [log in to unmask]
>
>I have been tasked with coming up with a figure for planning purposes,
>relating to how much bandwidth is reasonable per user in a residence
>facility.
Even modest levels can quickly aggregate to massive requirements, if you
treat the requirements as hard guarantees and you don't oversubscribe...
Assume even three thousand students...
256Kbps committment --> 768Mbps (OC12+)
56Kbps committment --> 168Mbps (OC3+)
Or do the math backwards... if you are willing to provision a full 45Mbps
DS3 for 3000 students, what kind of bandwidth would that work out to per
student? ~15Kbps...
>Understanding that reasonable is subjective, what are other people using for
>design guidelines? In the simplest situation, is it reasonable for a single
>student in a Residence Facility to have 64Kbps access? Then, toss in what
>is acceptable oversubscription and subtract the small number of students
>that do not come to campus with a computer.
Of course, the reality is that:
-- ANY reasonable provisioning scheme would include substantial
overcommitment (and the larger the number of users aggregated,
the heavier the overcommitment can practically be)
-- Your load is liable to asymetric (normal web browsing load will
resulting in inbound load levels controlling your bandwidth
requirements; an infestation of servers running from the
residence halls can invert that condition)
-- Your load will be highly time phased; a typical pattern for
many residence hall networks is to be hot in the evening,
a time when bandwidth requirements from campus offices and
labs may be low (--> you may NOT want to provision separate
capacity for your residence halls and your main campus, given
that the load is time phased in a way that may be fortuitous).
-- A tiny fraction of users are going to consume the greatest
fraction of the bandwidth while most users will consume
negligible amounts; a prudent strategy, then, is to focus on
those who consume the most, and work one's way downward from
there (of course, this implies per port flow data for the
network)
-- You can substantially reduce bandwidth requirements by using
passive web caching and NAT boxes (to effectively reduce or
eliminate unathorized servers) -- but note that a loss of
transparency is part of the price you'll pay for that bandwidth
control
-- Local congestion can really "help" you -- if you are worried
about bandwidth, shared 10Mbps hubs will result in less traffic
than switched 100Mbps infrastructure, for example.
-- What you provision may be more determined by what your budget
can underwrite than anything else, in the final analysis...
Regards,
Joe
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