Is this claim true, or not?

[Charles Steinkuehler]

Seth Dimbert wrote:
> PLEASE: let's not let this become a debate of TWC vs. Everest or such
> things... Can anyone give me the straight dope?

This gets ugly and complicated, because there is more than simply the 
"last mile" (here defined as the link between you and your ISP's 
network) involved in what most folks are referring to when discussing 
"Bandwidth".

Yes, the "last-mile" bandwidth for cable-modem connections will slow 
down based on how many of your neighbors are currently donwloading Pr0n 
(or otherwise generating high-bandwidth traffic).  This effect does not 
happen with xDSL, where there is a unique head-end circuit for each 
customer.

This does *NOT* however, mean that cable is better (or worse) than DSL. 
  For instance, I was on a high-speed ADSL link with SWBT before I moved 
my office, and I saw my usable bandwidth drop from well over 1.5 MBits/s 
down to sub 700 KBits/s before I switched to an SDSL provider for 
greater upstream bandwidth.  The drop was *NOT* due to anything related 
to my DSL link, but has everything to do with the fact that SWBT 
oversubscribes their upstream bandwidth (note: EVERYONE does this, the 
big question is how much they oversubscribe, which is something you'll 
never get any consumer ISP to tell you).

To truely judge an ISP, you have to factor in not only the bandwidth and 
type of the last-mile link, but also the ISP's internal network 
structure, their upstream connections, and maybe even one or two more 
layers of upstream links, until you get to the internet backbone.  You 
want to see multiple upstream links to backbone providers with good 
peering arrangements to other carriers.

As another example, I have some servers on a 100 MBit/s link to the 
"internet" provided by Cogent.  Cogent runs a non-blocking optical 
backbone which guarantees a full 100 MBit/s to anywhere on Cogent's 
network.  Once I try to access something outside the Cogent network, 
however, I'm fighting with all their other customers for limited 
bandwidth at the handful of peering points that link Cogent with the 
internet, so maximum bandwidth is typically *FAR* less than 100 MBits/s 
to anywhere on the actual "internet".

If the above hasn't completely confused you, I have had both DSL and 
Cable-Modem connections personally, and know numerous folks in other 
regions who have also had DSL and/or cable-modems.  As a general rule of 
thumb, I would have to say Cable-Modems are better, assuming the 
cable-modem folks and the DSL folks are both doing an OK job of running 
their networks.  If the system admins are utter bone-heads (or are 
forced to be bone-headed by managment decree), DSL seems to deteriorate 
a bit better than Cable-modems (ie a poorly run DSL network will operate 
better than a poorly run cable-modem network).

The other thing to watch for with cable-modem service is area-by-area 
variation in service quality.  In all the town's I'm familiar with, 
there are regions where cable-modem service totally *ROCKS* (ie where 
the yuppies, lawyers, and city-council types who can make life hard for 
the cable-company if they desire live), and regions where service 
absolutely *SUCKS* (ie the "wrong side of the tracks", where no one 
cares if the folks complain).  The only way to know which sort of area 
you live in is to check with your neighbors.  Even then, remember 
everything can change in a few months, when your ISP (either DSL or 
cable-modem) signs up another few thousand customers and doesn't add any 
upstream capacity (or add nodes to the cable modem network).  I have not 
seen DSL experience these sorts of problems, since this is pretty much 
caused by a lack of cable-modem node density, which doesn't apply to 
DSL.  While it would be possible to regionally prioritize traffic once 
it got on the ISP's internal network, this would require work by a 
competent network admin (ie probablility of actually happening 
approaches zero :), and would likely get the ISP's in lots of trouble if 
word of it ever leaked out.

Bottom line, networks are big, complex things.  No single metric will 
tell you how good or bad a particular network is (for instance, it's a 
not uncommon practice for some ISP's to prioritize "ping" traffic, so 
gamers will think their network is blazingly fast, when in fact their 
UDP gaming packets get flagged as "bulk", and experience 50% or higher 
packet loss along with massive latency).  Lost traffic is another killer 
of bandwidth...I've gotten faster speeds on general browsing (but slower 
bulk downloads) by reducing my downstream bandwidth to get rid of packet 
loss on a marginal DSL link.

Pick an ISP with a good technical staff, and good upstream connections 
(you can ask about this, and do traceroutes into their network to find 
out who's providing them connectivity) and you probably won't go too far 
wrong.

-- 
Charles Steinkuehler
charles at steinkuehler.net