2 Wire T1 - HDLC

Barton F Bruce barton at cent.net
Wed May 16 17:50:01 UTC 2001

Even pre-HDSL2 vendors such as PairGain had single pair full T1 solutions,
but that suffered slightly in loop length capabilities compared to the 2
pair HDSL they were then selling.

We still have some of the older ones in use.

Now with HDSL2, they get the same range as 2 pair HDSL but use only one

But what we really should be talking about is something else.

We need to be able to provide the customer end of HDSL2 while the ILEC
provides the CO end for a lower cost local T1 loop that can still connect to
traditional other points in the network as any normal T1 can and does not
depend on a CLEC colocating a DSLAM for the savings.

If an ISP buys DSL transport from Verizon to connect his remote customers to
his Verizon ATM T3, he may use *ANY* suitable DSL box at the customer's end.
It could be a cisco 827 or some far less expensive other brand. It is
Verizon's DSLAM at the CO, but his IP addresses and service the customer

Here in the states, everyone uses ISDN U interface for the BRIs (i.e. we
provide our own NT1 function), not the S/T interface others suffer with, and
we provide our own CSU/DSU for other services.

But on standard T1 services (the prototypical EXPENSIVE last mile) we still
must $pay$ for *their*
HDSL2 box as it is part of a tariffed service.

Sure as a CLEC one can get copper pairs and do HDSL2 form COLO, but there
are situations where low density customer locations simply don't justify
colocating in THAT CO, and getting a LEC T1 type-2 end loop but at an even
lower price where WE provide the HDSL2 at the customer end (built into a
cisco router, even), and the ILEC provides the CO end would be a step
towards dragging T1 loop pricing down nearer ADSL pricing.

Other than loss of revenue, this is no worse for the ILEC than U interfaces
or their DSLAMs feeding customer owned cisco 827s.

----- Original Message -----
From: "Martin, Christian" <cmartin at gnilink.net>
To: "'John A. Tamplin'" <jat at liveonthenet.com>; "Hunter Pine"
<hunter at compuhelp.com>
Cc: "mike harrison" <meuon at highertech.net>; <nanog at nanog.org>
Sent: Tuesday, May 15, 2001 1:07 AM
Subject: RE: 2 Wire T1 - HDLC

> John,
> I believe you are referring to HDSL2, which can and does run over
> single-pair but uses advanced spectral shaping and error correcting
> mechanisms that weren't invented when HDSL was dreamed up by Bellcore.
> ./chris
> > -----Original Message-----
> > From: John A. Tamplin [mailto:jat at liveonthenet.com]
> > Sent: Monday, May 14, 2001 7:13 PM
> > To: Hunter Pine
> > Cc: mike harrison; nanog at nanog.org
> > Subject: Re: 2 Wire T1 - HDLC
> >
> >
> >
> > On Mon, 14 May 2001, Hunter Pine wrote:
> >
> > > That was my mistake Mike. HDSL is NOT two SDSL lines by
> > definition. It's
> > > just two circuits running symmetric 768k DSL (not SDSL)
> > bonded to form a
> > > single1.5mb line.
> >
> > Umm, no.  HDSL rides a single pair, and provides more than 1.5Mb.
> >
> > John A. Tamplin jat at jaet.org
> > 770/436-5387 HOME 4116 Manson Ave
> > 770/431-9459 FAX Smyrna, GA  30082-3723
> >
> >

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