[lug] Running Linux Servers over DSL

[Sean Reifschneider]

On Fri, Jul 30, 2004 at 04:29:28PM -0600, Timothy Klein wrote:
>as long as your line is clean, DSL is now as fast as T1.  Upload, which would 

Not quite as fast as a T1 line.  It's 1.5mbps, but that's raw line
speed.  As near as I can tell, that's the ATM cell rate for the line.
ATM cells use very small packets with about 15% overhead.  This is what
they call the "ATM tax" and means that the 1.54mbps DSL line actually
gets more like 1.25mbps on file transfers with TCP/IP.  This is what
I've seen on my lines.

A T1 is 1.544mbps true data rate.  Close, but not quite.

It also explains why the bonded DSL lines that I've been playing with
only get around 300KB/sec downloads and 200KB/sec uploads, where a pair
of bonded T1 lines will give more like 375.  Not bad for a pair of
$28/month lines either way, though.  I need to do some more work on the
bonding setup, though, I seem to run into instances where some sites
don't respond properly.

>affect the server more, is slower).  Just make sure that your ISP allows the 
>server stuff, but I think all do.

Most put some sort of bandwidth cap on it or do not allow servers.  For
example, FRII charges for traffic after so many GB/month, and NeTrack
has an "unlimited" plan that is behind a firewall, or a metered plan
which is not.  Unfortunately, bandwidth is still pretty expensive for
the "little guys" (meaning pretty much anything under a OC3).  QWest is
one of the few that offers unlimited traffic with no filtering.

>No bandwidth cap is nice for piece of 
>mind, just in case your server were to become Slashdotted for some odd 
>reason.

Except that most slashdottings last *WELL* under the 95th percentile
time, they really aren't that much traffic unless you're serving up a
bunch of big files.  And then, your DSL line is probably going to get
way oversaturated, yet still drop off very quickly.  None of the times
we've been slashdotted has it really impacted our service.  The first
time our web server was running on a P100, even.

>The only thing you will lose, I think, is you most likely have a much higher 
>guarantee of service with T1.  If you are depending for anything vital on the 
>line, your T1 will get fixed much quicker than DSL, should something go 
>wrong.  At least in theory.

Yeah, in theory.  We had a T1 to our house about 6 months before they
started offering DSL in Colorado.  The T1 was up and down for most of
the time.  They also charged us nearly 20% over what we had signed a
contract for.  We finally canceled the line and switched to DSL when
they told us they had to re-write the contract.  The DSL was much more
stable over the next 6 months than the T1 had been in the first 6
months, but they had just moved the T1 to new pairs a week before we
canceled and it was rock solid.

While DSL is pretty good, I will say that in general the T1s we manage
are more reliable.  DSL is very close, though.

Sean
-- 
 I think you are blind to the fact that the hand you hold
 is the hand that holds you down.  -- Everclear
Sean Reifschneider, Member of Technical Staff <jafo at tummy.com>
tummy.com, ltd. - Linux Consulting since 1995.  Qmail, Python, SysAdmin