mailing list archives
Re: People who purchase unproven technologies to support their Business, and whine about it. RE: To CAIS Engineers - WAKE UP AND , TAKE CARE OF YOUR CUSTOMERS
From: "John A. Tamplin" <jat () liveonthenet com>
Date: Mon, 14 May 2001 10:35:05 -0500 (CDT)
On Mon, 14 May 2001, mike harrison wrote:
You are aware that a good percentage of the T1's you purchase nowadays are
just a pair of bonded 768 dsl lines, right? The phone companies have been
doing that for over 20 years to save on copper.
Just for starters: HDLC circuits run on different voltages, have timing
and a bunch of other characteristics that xDSL never heard of.
I am confused -- HDLC is a link-level protocol which has nothing to do
with voltages, and since you compare it to xDSL you can't have meant HDSL
instead. If you meant T1 instead (which can carry 24 DS0s of digitized
voice, PPP, or other protocols besides HDLC), remember that a POTS line
has very different characteristics than an optical signal, yet aside from
the last mile they are mostly carried over fiber, encapsulated in a T1
frame which is encapsulated in a T3 frame, which is encapsulated in OCx,
etc. Likewise, a point-to-point T1 doesn't have much in common with an
ATM PVC, yet you can carry a T1 across an arbitrarily complex ATM network
using circuit emulation. (Yes, I am talking about the US system here, and
I know elsewhere is different but a similar concept).
We are seeing BellSouth run 2 wire T1's, which have been working well so
far. Still not DSL (approx 900mhz over POTS). --Mike--
AFAIK, the 2-wire T1s are in fact carried over HDSL to the smartjack, and
the smartjack extracts the T1 -- I have two of these in my house, using
Pairgain (now ADC)'s HiGain Solitaire H2TU.R402 for T1 transport. The URL
of the frame describing the product line is at (minus any line breaks or
spaces added along the way):
This specific card is under HDSL2 RT Modules.
John A. Tamplin jat () jaet org
770/436-5387 HOME 4116 Manson Ave
770/431-9459 FAX Smyrna, GA 30082-3723