casey@gauss.llnl.gov (Casey Leedom) (01/09/91)
I just moved into a house in the Berkeley hills. I plan on
tele-commuting to work several days a week using an X terminal and
V.32 over Telebit T2500s (GE7.00 PROMs.)
Unfortunately, my V.32 connections keep on dropping after anywhere
from 45 minutes to an hour and a half. When I examine the line
quality register, S78, it's 100 both before and after the connection
drops. It appears that the T2500s can maintain a PEP connection
forever, but the ``instantaneous'' transmit and receive bit rates, S70
and S72, are very low, in the 12K-15K range. When I look at the bit
assignments per PEP sub-carrier, I see a curve that looks like the
following:
6 | ------ - -----
4 | - -------------------------
2 | ---------
0 |-- - - -----
whereas the typical PEP bit assignment curve I've observed looks more
like:
6 | ------ - -------------------------------
4 | - -------
2 | --
0 |-- - - ----
(Sorry I can't give you exact figures -- I need to hook up a PC of
some kind to capture the data from the modem but I haven't had to time
to borrow one yet.)
I've been told that the two zero drop outs are for the PEP
retraining signals. The big issue is that the mid and high frequency
sub-carriers don't seem to be up to snuff.
I asked PacBell to come out and test the frequency response of the
line outside and inside the house to determine whether it was ``their
problem'' or my house wiring, but they don't seem to be able to do
that. Amazing. Apparently there used to be a PREFIX-00XX number that
the service technicians could call that would provide a 0DB frequency
sweep, but all they've got available now is PREFIX-0020 which provides
a 1004Hz tone at 0DB. I can't tell whether the central office was
jiving the technician who came out (he made a real and very valiant
effort to help me -- this is my second great experience with PacBell
service technicians by the way) or whether they really don't have any
method of doing a frequency response test.
I suppose their attitude could be that there's really nothing simple
(read "cheap") that can be done if there is a frequency line
impairment, so why bother test -- besides, it would give the customers
something solid to bitch about (corresponding computer programming
maxim: ``Don't test for bugs you either can't fix or don't want to
deal with.'')
The service technician who came out also mentioned that my house is
just about as far from the central office as I could get without being
assigned to a different CO. However, he thought that all the street
wiring was fairly new. By the way, the drop to my house is twisted
six-pair.
The other possible source of these problems is the house wiring.
The wiring in the house is very old, untwisted aluminum three-pair.
Yes, I said aluminum! Don't ask me -- everyone I've told of and
showed the wiring to says they've never heard of aluminum being used
for telephone wiring ... and some of them have been in the telephone
business for over twenty years!
I'm running a voice circuit on line one (green/red -- tied to the
white-blue/blue-white pair in the three-pair) and the modem on line
two (black/yellow -- tied to the white-orange/orange-white pair of the
three-pair.) The white-green/green-white pair of the three-pair is
unattached and unterminated.
There's about forty feet of the wire strung between the drop box and
the telephone jack I'm trying to use. It's also wired serially
through a jack about ten feet from the drop box. That earlier jack
has a telephone set on line one, but nothing on line two. The far
jack also has a telephone set on line one in addition to the modem on
line two.
While in PEP mode, I can hear a very small amount of cross talk when
both the modem and voice lines are idling (very low level regular
clicking.) As soon as the modems start up it becomes nearly
impossibly to hear the cross talk. I don't think I can hear any cross
talk when using V.32.
In any case, because I wasn't able to get anywhere with PacBell, I'm
left to simply replace the wiring in my house an hope that that clears
up the problems.
So, the point of this article:
1. I welcome any comments about frequency response testing and
getting PacBell to fix their wiring if it's the problem.
And just what are the nominal levels of service that they
do promise to provide?
2. I welcome any comments about the potential problems that very
old, untwisted aluminum wiring might generate and in particular,
does anyone think it could be responsible for my frequency
response loss?
3. I think I remember hearing, perhaps in this group, that twisted
pair wiring can actually *degrade* frequency response because of
capacitance coupling. Am I dreaming that up? Will I be doing
more harm than good by running copper twisted pair?
4. We're thinking of running twisted copper six-pair throughout the
house to accommodate future expansion with an Ethernet, AppleTalk
net, and up to three phone lines. Does anyone see any problem
with cross talk doing this?
Thanks for any help you may be able to offer. Since this is such a
broad question, may spark a lot of discussion, and be of interest to a
lot of people, I think that posting followups would be best rather
than sending me mail.
P.S. I just learned about the ATJ6J0 command. Here's the output of that
command after one of my line drops. Unfortunately I have no idea
what the output means ... Is the interpretation of this output part
of the ``Undocumented Features'' document by Telebit?
ATJ6J0
R000000 R000 N003 EC000
T000000 F000000 R000000 M000000 E000000
F000000 000000
000 000 000
001
000 000 000 000 L L T000
M000 L001 C000
OK
Thanks,
Caseykgdykes@watmath.waterloo.edu (Ken Dykes) (01/10/91)
In article <15903@accuvax.nwu.edu> casey@gauss.llnl.gov (Casey Leedom) writes: > The other possible source of these problems is the house wiring. >The wiring in the house is very old, untwisted aluminum three-pair. >Yes, I said aluminum! Don't ask me -- everyone I've told of and I wouldn't worry so much about Aluminum, but UNtwisted? eeeeeek! > There's about forty feet of the wire strung between the drop box and >the telephone jack I'm trying to use. It's also wired serially >through a jack about ten feet from the drop box. That earlier jack >has a telephone set on line one, but nothing on line two. The far Does your wiring-run pass any furnace/air-cond/water heater/etc which may have a relay/starter going about every 45 minutes? perhaps when it "starts" you get some sort of induction pickup on your wires. Also, do your mid->high frequency response problems occur at harmonics of 60hz (ie: your phone wires pass hydro wires, the 60hz induction provides a possible dampening effect?) [caveat: I really dont know what I'm talking about.] > While in PEP mode, I can hear a very small amount of cross talk when >both the modem and voice lines are idling (very low level regular Cross-talk will disappear with twisted pair (or at least "very small" levels will :-) > 2. I welcome any comments about the potential problems that very > old, untwisted aluminum wiring might generate and in particular, > does anyone think it could be responsible for my frequency > response loss? I think UNtwisted is unwise at best of times, heck, bite the bullet install lots of twisted pairs and run Ethernet all over your house :-) > 3. I think I remember hearing, perhaps in this group, that twisted > pair wiring can actually *degrade* frequency response because of You got it backward in my belief. > 4. We're thinking of running twisted copper six-pair throughout the > house to accommodate future expansion with an Ethernet, AppleTalk > net, and up to three phone lines. Does anyone see any problem Yes, yes, capacity planning! wire is cheap, the "running it" is a pain, do it once, but run a lot of pairs. Ken Dykes, Software Development Group, UofWaterloo, Canada [43.47N 80.52W] kgdykes@watmath.waterloo.edu [129.97.128.1] watmath!kgdykes postmaster@watbun.waterloo.edu B8 P6/6 s+ f+ m t w e r p
IZZYAS1@mvs.oac.ucla.edu (Andy Jacobson) (01/22/91)
Casey Leedom <casey@gauss.llnl.gov> writes: >Apparently there used to be a PREFIX-00XX number that the service >technicians could call that would provide a 0DB frequency sweep, but all Well some places they still do ... in 415, you could try NXX-0046. This motif is by no means universal though. I do know that in S.F., (where the protesters are burning CHP cars right now) 431-0046 will provide sweep tone, but I don't know the range or response. Andy Jacobson <izzyas1@oac.ucla.edu> or <izzyas1@UCLAMVS.bitnet>
forrette@cory.berkeley.edu (Steve Forrette) (01/24/91)
In article <16264@accuvax.nwu.edu> Andy Jacobson writes: >Well some places they still do ... in 415, you could try NXX-0046. >This motif is by no means universal though. I do know that in S.F., >(where the protesters are burning CHP cars right now) 431-0046 will >provide sweep tone, but I don't know the range or response. People outside the bay area can feel free to try this, as the call never supervises. (The downside of this is that you can't use it to haze people with three-way calling! :-) :-) ) Steve Forrette, forrette@eccs.nwu.edu