haleden@ncar.ucar.edu (Hal Eden) (06/23/89)
I'm sure that this has been discussed here before, so if you reply
to me, that would be fine.
Could someone give me a semi-technical explanation for those {{{{{{{{
which appear as interference at 1200 baud? I am going round and round
with USWestComm about this.
About a month ago a new office was installed in Boulder (apparently a
DMS100 ? 3rd hand info) and ever since then I have had to re-call
numerous times to get a "clean" line. It seems that discussions I
have seen in the past referred to something being "out-of-phase".
What exactly is out of phase? Whose responsibility is it? How would
be the best way to pursue this? I have gone through several levels of
supervisors and still get "no satisfaction". I am not the only one
with the problem, and I have pursued it from the "other" end (the
problems only happen when I call modems at the university where I
work). Apparently the problem has been fixed for most people, but I
am served by a different central-office than most of my colleagues.
Here's some idea of the interaction from this end --
Calls 1-3: I have "data noise" (with description) on my line
response 1-3: your line checks out, must be your equipment
counter response: but I can call englewood, denver, elsewhere with no
problems; I only get this when I call the university in boulder!
Call 4: Escalate, supervisor says he will check it out
call 5: no response so I call again this time another supervisor gives
me a (next level) supervisor, this supervisor gives me a spiel
about how above 300 baud they cannot guarantee anything
without me acquiring a "conditioned line"
my response: well, let's see; a conditioned line from where to where?
answer: from your home to the central office.
resp: and don't I go through that same central office when I call
denver, englewood, etc?
answer: yes
resp: then why do I need a conditioned line from my house to the
central office when when I go via that path to denver,etc I
have no problems?
answer: I don't know. Well maybe you could turn down your bauds a
little bit, say to a thousand or so and see if you still have
the problem....
me: sheesh!
so HELP, can someone educate me a little bet so that I can better
communicate what the problem is AND perhaps point me to the sort of
department within the operating company which would understand the
problem and could do something about it? I am primarily a software
person who knows enough about hardware to get my self in trouble, and
have worked at a company who was working on an integrated phone/data
network/workstation (but I was in the database group not the telecom
group) so I know some small amount of terminology related to this, but
not a lot, so too low level a description might lose me, but I don't
need a laymans explanation either.
thanks
hal
haleden@boulder.colorado.educlements@bbn.com (06/26/89)
>Could someone give me a semi-technical explanation for those {{{{{{{{ >which appear as interference at 1200 baud? I am going round and round >with USWestComm about this. > [Saga, involving new phone exchange in the area, deleted.] Assuming that the errors happen at a quite steady rate, this is the problem known as "clock slip" or "frame slip" on a digital inter-office trunk. The basic concept is that all the digital phone exchanges and trunks in the USA are supposed to be run from one master clock! That is, the 1.544 MHz frequency on all T1 lines (and related ones on other lines) and the internal clocks of the digital exchanges which pass samples through them are all supposed to be locked together. If they are not, one end will supply bits slightly faster or slower than the other end will consume them. When this happens, and the error builds up to the length of one sample on the trunk, all channels on the trunk drop or gain one digital sample, causing a phase error of 1/8000 second, typically causing the data error you are seeing. So the new exchange, or some of the trunks through it, are not properly phase-locked to the rest of the system. Fixing it is PROBABLY just a matter of flipping a configuration switch (in hardware or software) to establish master clock distribution correctly through the system. The hard part is finding one of the few people in your local TELCO who understands the issue. Keep asking for technical supervisors until you find someone who sounds like they recognize the concepts of master clocks and phase locking and frame slip on a digital trunk. You may have to find a name at the "engineering" department of the TELCO, who normally don't deal directly with customer complaints, and get them to work back from their side. They probably specified the system and would be annoyed that it wasn't implemented correctly. >thanks >hal > >haleden@boulder.colorado.edu Bob Clements, K1BC, clements@bbn.com
ceb@csli.stanford.edu (Charles Buckley) (06/27/89)
Concerning the following: From: clements@bbn.com Newsgroups: comp.dcom.telecom Date: 25 Jun 89 19:56:49 GMT >Could someone give me a semi-technical explanation for those {{{{{{{{ >which appear as interference at 1200 baud? Assuming that the errors happen at a quite steady rate, this is the problem known as "clock slip" or "frame slip" on a digital inter-office trunk. That may well be, but it can also simply mean that the isolation relay in the modem has dirty contacts. I had a 1200'er which would work error free for a month or two, and then start to generate such errors, at a more or less steady rate too. To fix it, I would open it up, pop the cover off the relay, clean it with electronic solvent (doing my share for the ozone layer, I'm sure ;-{), and then be okay for two more months. I just bought a new modem, and was surprised to find such a relay still present. I guess they're needed for FCC regulations, or something, but my ideal solution would probably use silicon and *no* *moving* *parts*. One easy way to tell if this is what needs to be done is to thwack on top of the modem. If that gives you a fistful of {'s, then clean the relay, and leave the poor functionaries at the telephone company alone.
ch%maths.tcd.ie@cunyvm.cuny.edu (Charles Bryant) (07/01/89)
In article <telecom-v09i0211m01@vector.dallas.tx.us> boulder!sigi.Colorado.EDU. colorado.edu!haleden@ncar.ucar.edu (Hal Eden) writes: <X-TELECOM-Digest: volume 9, issue 211, message 1 of 7 <I'm sure that this has been discussed here before, so if you reply <to me, that would be fine. <Could someone give me a semi-technical explanation for those {{{{{{{{ <which appear as interference at 1200 baud? I am going round and round <with USWestComm about this. When a V.22 (or Bell 212) modem gets a single bit error (when no data is supposed to be being transmitted), this gets turned into a DEL character (which normally is not seen on the screen) and a '{'. This is due to the scrambling used with this type of modem (the scrambling is used to spread the frequencies used). <About a month ago a new office was installed in Boulder (apparently a <DMS100 ? 3rd hand info) and ever since then I have had to re-call <numerous times to get a "clean" line. It seems that discussions I <have seen in the past referred to something being "out-of-phase". <What exactly is out of phase? Whose responsibility is it? How would There should be nothing that can get 'out of phase'. <so HELP, can someone educate me a little bet so that I can better <communicate what the problem is AND perhaps point me to the sort of <department within the operating company which would understand the <problem and could do something about it? You have described the problem perfectly. If you can get a clean line by redialling it must be a problem between the exchanges (damn!). cb -- Charles Bryant. Working at Datacode Electronics Ltd. (Modem manufacturers)