[OT] Re: DSL Coming -- I may need help! : My ranting :)

From: Jay West <west_at_tseinc.com>
Date: Mon Feb 28 20:13:07 2000

Bruce wrote...
> connection! It'll be (minimum) 256K up/downstream guaranteed, and those
> rates could fluctuate a bit depending on the usual variables.

Um... you might want to check the fine print on the DSL service agreement.
At least in SWBell (and I strongly suspect it's also true in other DSL
carriers infrastructure) DSL speed guarantees are only from the copper jack
in your house to your central office DSLAM. When your DSL traffic hits the
DSLAM it is moved off from the PSTN to a cell relay ATM network, where all
the DSL-offering ISP's (including SWBell if that's your ISP) actually
compete for bandwidth availability. As a result, DSL speed guarantees have
absolutely NOTHING to do with the internet speed you get. I won't go into
examples, but I'm sure many folks here will immediately see the
ramifications of this. Think of a file download where each packet comes at
256k but there's 300ms pauses between each packet!

Add to this that most ISP's are implementing PPP over ATM for
authentication, so there's also some minor extra overhead in addition to the
above cell relay latency.

Not to mention that DSL traffic is carried as UBR (unspecified bit rate) on
the ATM cell relay network. This means no QOS, no commited cells, no
standard ATM service classes of any kind! UBR basically means "We might get
your packets there if we have absolutely nothing else to do. Then again, we
might not".

Just my own 2c worth.

Jay West
Received on Mon Feb 28 2000 - 20:13:07 GMT