chen@cunixc.cc.columbia.edu (Bill Chen) (12/11/88)
We've been having progressively worsening noise problems on our dial
up modem pool for our PBX. It seems to occur mainly at nights and
consists mostly of "{" characters. These { comes periodically, about 1
every 30 secs to 2 minutes. Sometimes we get bursts of noise too. We
have checked the modems, Racal Vadic VA4492Es and the PBX, IBM/ROLM
9751 and neither seem to be the cause. We don't run error correction
such as MNP although our modems are equipped to do it. The noise
seems to be generally one way, from the host side to the terminal side.
Although recently, noise does seem to get to the host too.
Telco people haven't been too helpful. Calling 611 is useless. Trying
to talk to someone technical within the telephone company is next to
impossible.
Are there any people out there that may have seen this problem? I have
been told by some people that there might be some notch filters that
can cause this kind of noise. I don't know much about telephony
things, but maybe someone out there in netland can shed some light.
Thanks in advance.
Bill Chen
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_____________________________________________________________________
William Chen chen@cunixc.cc.columbia.edu
Network Planning 854-7593, 854-2455, 280-2455
Columbia Universityearly%css.DEC@decwrl.dec.com (Bob Early CSS/NSG dtn 264-6252) (12/12/88)
>From: chen@cunixc.cc.columbia.edu (Bill Chen) >Subject: Modem noise >Date: 11 Dec 88 00:28:10 GMT >We've been having progressively worsening noise problems on our dial : : >such as MNP although our modems are equipped to do it. The noise >seems to be generally one way, from the host side to the terminal side. Noise is just that. Random impulses being picked up by the telco lines as they pass through an 'electrically' noisy environment. Some such causes are elevator shafts; rotary machines (a such as motors, generators, and 'dynamos'), other wires such as HVAC transmission, poor grounding of the computer vequipment,; archaic telco equipment (step-and-select strowger swithches, etc). If you have the option of using MNP, use it. >Telco people haven't been too helpful. Calling 611 is useless. Trying >to talk to someone technical within the telephone company is next to >impossible. With most telephone companies you must be persistent,and give the impression that you *know* it is in the central office, and they *must* fix it. (I personally had a defective phone service, and it took three months to get it fixed.) >Are there any people out there that may have seen this problem? I have >been told by some people that there might be some notch filters that This is a common problem with BELL 212A implementations. The "{{{" or 'curly bracket' isn't *really* the true character. The curly bracket is the modems interpretation of the noise impulses it is seeing, in much the same manner if you privide a string of randoms 'ones and zeros' to a computers operating system you will see many 'odd' charcters as the CPU attempts to 'parse' the charcters. >Bill Chen Bob Early "Long live the Scholar-Plus" [Moderator's note: The phone company seems to think their customers are all dumb. Remind me to tell you about the time I spent several days convincing Repair Service that a bummed out interoffice trunk between Chicago-Kenwood and Chicago-Wabash was not '...a problem with my instrument, which will require our representative to visit your premises a week from next Tuesday...'. I was finally able to sneak in through the 'back door' and speak to the supervisor in night plant about two in the morning. I held up the troubled trunk on one of my lines while he went in the frames, found me and busied it out. But should customers have to do this sort of thing for Bell? Pat Townson]
ssr@cos.com (Dave Kucharczyk) (12/14/88)
In article <telecom-v08i0198m03@vector.UUCP> chen@cunixc.cc.columbia.edu (Bill Chen) writes: >X-Administrivia-To: telecom-request@vector.uucp >X-TELECOM-Digest: volume 8, issue 198, message 3 > >We've been having progressively worsening noise problems on our dial >up modem pool for our PBX. It seems to occur mainly at nights and >consists mostly of "{" characters. These { comes periodically, about 1 >every 30 secs to 2 minutes. [rest of description deleted] I had this problem for a few months when i moved to a place served by a #5 ESS. the problem is that the T1 line between two offices is not synced properly which causes the bit stream to slip (ie the offset between the two clocks becomes greater than one pulse width and a bit is missed). Why this causes "{" to appear I haven't figured out yet. My friend posted something about this (he got them to fix it), so I'll just repost it. dave [the entire message appears in 187...here are excerpts] .........forget to install, or improperly configure a board in the T1 carrier system equipment (this is not the analog switch, but before the switch) called an "OIU board". He didn't know what OIU stood for, but he tells me that it's fairly standard telco terminology. He said that this board provides the clocking for the link going from the analog office to the digital office. Without the board, the T1 carrier system uses a different clocking source (presumably an internal clock within the T1 equipment) which is not always quite in sync with the correct source. That's why things appear to work ok for voice, but not for data......