OT: DSL Woes

From: Eric J. Korpela <korpela_at_ellie.ssl.berkeley.edu>
Date: Fri Jul 20 12:46:13 2001

> I seem to remember reading that the former RBOC's are required to provide a 256k
> minimal transfer rate in either direction, while the cable service providers
> have more latitude. Everyone I know who's got/had the AT&T cable modem service
> has had lower slower transfer rates. My understanding is that AT&T is
> provisioned such that they can provide the full 256Kb to one block (whatever
> that means, but presumably a city-block, since that's how they're physically
> structured) and that's what the customers on that block have to share. I find
> that a little hard to swallow, but it's possible, since these companies are run
> by bean-counters.

Yep, I generally get about 240 kbps upload from my cable modem. The 4-6 Mbps
typical download makes up for the lost 16 kbps. Biggest problem I have with
my cable modem is latency which can be 100 to 300 ms (round trip) at times. It
can be annoying for shell access. Then again, I still remember getting
30000 ms latency the consoles of overworked unix machines as an undergrad,
so I can cope

> Though the statistics my DSL modem software provide suggest I receive lots of
> bandwidth, my transfer speeds vary widely. I have made a few cursory tests, and
> found on one occasion, that when I used my notebook via dialup on the voice
> line, at 56Kb, I got faster transfer (concurrent transfer of the same file from
> the same place took WAY less time) than concurrently and through the same ISP
> via my DSL connection. Weird!

Transfer times are dominated by bottlenecks that could be anywhere in between
you and the source. All bandwidth is shared bandwidth. Your 56k modem
connected to another modem on the other side of the DSL bottleneck, meaning
a bunch of DSL users were sharing a small pipe somewhere.

Last time I checked, ISP's were paying about $600/mo/Mbps for
connectivity. That means if they've got 100Mbps to the backbone, they
need to share those costs among 2000 users at $30/mo before they can
even think about making a profit (making the bad assumption no other
costs are involved). In other words, your ISP is betting that
your monthly average transfer rate is substantially less than 50 kbps. Ever
wonder why DSL and cable providers get upset when people paying residential
rates try to set up a server?

It also means that when all 2000 users try to download porn simultaneously
their data rates are going to drop to <50 kbps.

Of course the same is true at both ends of a connection.

Eric
Received on Fri Jul 20 2001 - 12:46:13 BST