SDSL vs T1 (was Locations with no good Internet)

Isn't this really an issue (political) with tariffed T1 prices rather
than a technical problem?

Yes, of course. It's even worse if you are tied to one particular ISP
(VZB) by non-portable IP addresses.

I wanted service from AS701 with a V.35 hand-off; both requirements
(the ISP choice and the hand-off type) were/are for sentimental reasons.
Speed was/is a lower-priority concern, i.e., I was/am willing to live
with sub-T1 speeds if it allows me to keep my 701-assigned IP addresses
for a lower monthly extortion payment.

My choices were:

1. Get a T1, enjoy the bandwidth (I live in an alternate Universe in
   which T1 bandwidth is almost infinity) and the SLA, and getting a
   V.35 hand-off would have been as easy as pulling an Adtran DSU out of
   my junk pile. But it was something like $650/month, probably before
   adding taxes and other extortions.

2. Opt for SDSL instead. I'm within a short walk of my CO, but I opt
   for only 384 kbps to reduce the monthly extortion payment. And since
   I still want V.35 hand-off, add the expense of designing and building
   my own CPE for it - but it's a one-time expense, and I have learned
   a *lot* in the process - as they say, happiness is a journey, not a

I was told that most T1s are provisioned over a DSLAM these days
anyways, and that the key difference between T1 and DSL was the SLA
(99.99% guarantee vs. "when we get it fixed").

My situation is different because I am deliberately opting for a lower-
speed service than what's available. At sub-T1 speeds SDSL has one
advantage: the actual electrical signaling rate on the circuit is
lowered to match the subscription data rate, unlike the fractional T1

But if you are specifically looking for a 1.5 Mbps service and are
prepared to pay for 1.5 Mbps, the T1 vs. SDSL trade-off starts to look

* With a T1 regardless of who serves it to you and how, you still get
  the classic HDLC encapsulation supported by every decent WAN router;
  with SDSL served out of a Covad DSLAM you get ATM cells on the line,
  wrapped in a wacky frame format:


* Prior to my invention of the OSDCU gadget, it was not possible to
  connect a Covad SDSL line to a real router like Cisco (or Juniper or
  a BSD/Linux box or whatever), only to some very inferior router brands
  supplied as the "standard CPE". And as far as my gadget goes, I've
  built the hardware, but I haven't finished the firmware part yet, so
  it's still technically vaporware.

* ATM is much less bit-efficient than HDLC, so a Covad SDSL circuit sold
  as "1.5 Mbps" actually has a little less real data carrying capacity
  than a T1.

* I don't know off the top of my head what the monthly price is for
  Covad SDSL at 1.5 Mbps, and there probably is some variability between
  different ISPs who go through Covad, but I assume that even with a
  good deal it would still be a bit more than what I pay to VZB for
  384 kbps. T1 prices have been coming down OTOH, at least for those
  who aren't tied to VZB. But I still expect T1 to be at least a little
  more expensive than SDSL @ 1.5 Mbps. I don't know how big this price
  delta is right now though - would anyone here have a better idea?

The magnitude of this price delta ought to have a critical impact on
whether or not it is worth putting up with all the quirks of SDSL listed
above. For my peculiar situation (willing to live with 384 kbps and
tied to VZB) the price delta (>3x increase in the monthly payment) is
most definitely worth the one-time expense of finishing my OSDCU gadget,
but I don't know how the cards would fall for someone who is looking for
full 1.5 Mbps (or more with bonding) and who has a choice of ISPs.

And T3/DS3 can run over what, 4 copper pairs? Yet how much is the
typical tariffed rate for that?

DS3 over 4 copper pairs? ~11 Mbps symmetric on each pair? That seems
like squeezing a lot out of a copper pair to me. Over what distance?

The major difference between using HDSL smart jacks and classic smart
jacks is that the HDSL ones don't need wire that's in quite as good
shape and they don't need repeaters between you and the CO as often.
They're still very much a T1 service.

Yup. Even though at the transceiver chipset level HDSL and SDSL are
very much alike, the powers that be configure them very very differently
at the higher layers. HDSL units are configured to pass the entire T1
frame structure (SF/ESF) unaltered, and within that T1 frame structure
you get the good old familiar HDLC. Covad SDSL uses the same 2B1Q line
code as HDSL and even the same transceiver chip (Bt8970 or RS8973), but
stuffs the bit stream with ATM cells in a wacky non-standard frame
structure instead of HDLC or T1 frames.

One can either pay a monthly premium for a more standards-based bit
stream format, or pay less per month for the hoary non-standard Nokia
flavor and make a one-time expense of building a converter gadget to
transform it into HDLC (per FRF.8 or FUNI) as soon as it enters your


You missed an option. Just change to another ISP. I know of at least one AS701 address block still attached to a company that hasn't been their customer for ten years or so.