naftoli@aecom.UUCP (Robert N. Berlinger) (08/07/86)
I use a Multitech 224E modem to connect to our system from home at
2400 baud with group 3 MNP protocol. This all worked fine until
recently when it mysteriously stopped working. The modem works fine
on any other phone line, and also works fine at 1200 baud. 2400 is a
no go. I measured the voltage on the phone line and it was only ~13 volts.
I thought that all phone lines are supposed to be 48 volts (all others
that I tested were). Could this be causing the problem? It works ok
(a bit noisy and low volume) for voice.
How would I go about getting NY Tel. to fix this? They usually are unwilling
to listen to any problems dealing with data equipment.
--
Robert Berlinger
Systems Analyst
Albert Einstein College of Medicine
UUCP: ...{philabs,cucard,pegasus,ihnp4,rocky2}!aecom!naftoli
Compuserve: 73047,741bzs@bu-cs.BU.EDU (Barry Shein) (08/09/86)
>How would I go about getting NY Tel. to fix this? They usually are unwilling >to listen to any problems dealing with data equipment. >-- >Robert Berlinger Ok, due to circumstances, different BOCs etc it's hard to say anything that's absolutely true. I once found the following out from my local phone co (AFTER MUCH PERSISTANCE): You are right, if it is only a problem with data they start resisting you. HOWEVER, that is because they fix voice problems for free. After much persistance (I say again) I found out they would be "glad" to come out and clean up any problems such as you mention (bring it all up to spec) for (at the time) $150. Like I said, the problem is that the general repair folks don't seem to know about this. I think the way I finally got to the right people is I called and asked about leasing a modem for my home. When I got to that person (after a few calls) I asked "what if my lines are too noisy or something for the data", they told me about the above service and gave me a phone # to call. They also said if the problem was "out on the pole" they would repair that for no charge (I guess tho you are still stuck with the initial fee as they did come out, I dunno, it turned out in the end it was my modem after all.) The woman on the line was quite insistant that "on the pole" it should all be of data quality as they might have to support someone "on the same pole" (they love that phrase I guess) who is a bona-fide data customer (business I suppose.)* She also strongly suggested that I go down in the basement and unscrew the terminators, clean them up so they shine, and screw it back together as that (corrosion) is the problem 99% of the time. Check the voltage down there at the origin if you can. -Barry Shein, Boston University * Obviously this may not be at all true outside of a major city.
larry@kitty.UUCP (Larry Lippman) (08/09/86)
In article <416@aecom.UUCP>, naftoli@aecom.UUCP (Robert N. Berlinger) writes: > I use a Multitech 224E modem to connect to our system from home at > 2400 baud with group 3 MNP protocol. This all worked fine until > recently when it mysteriously stopped working. The modem works fine > on any other phone line, and also works fine at 1200 baud. 2400 is a > no go. I measured the voltage on the phone line and it was only ~13 volts. > I thought that all phone lines are supposed to be 48 volts (all others > that I tested were). Could this be causing the problem? It works ok > (a bit noisy and low volume) for voice. I am assuming that you measured ~13 volts when the telephone line was on hook (idle)... Sounds to me that you no longer have a "physical" pair from your home to the central office. In some congested or rapid-growth areas telephone companies adopt techniques to effect "pair gain". The most common technique is "added mainline carrier" (AML), which allows one telephone line to serve more than one subscriber line. The simplest version allows one physical line to provide one additional carrier line; the carrier line works by providing transmit and receive channels in the frequency range of 25 to 100 kHz. There is also a six channel version of this technique which uses a somewhat larger bandwith. In either of these applications, a subscriber line carrier terminal is provided in the subscriber premises. There is the older 1A Line Concentrator which uses an outdoor pole-mounted "demultiplexer". Transmission is not too bad on this type of system since the multiplexing is "space division"; i.e., by means of a crossbar switch, so there is no significant insertion loss or degredation of transmission. There are newer digital multiplexing systems, which also use a pole-mounted "demultiplexer". I have no first hand experience with these, but modem transmission impairment is a possibility anytime digital sampling and analog reconstruction is used. In general, telephone companies use the above techniques for low-traffic residential lines only (high-traffic business lines would defeat the purpose of this "statistical" multiplexing) - but anything is possible. AML is BAD NEWS for any type of data transmission; the reason is that the carrier frequencies are determined solely by L-C networks, and the circuitry can readily drift creating all sorts of transmission anomalies. An AML line (like Superior-Continental equipment) would present between 6 and 14 volts to the local subscriber loop - so it sounds like this is what you have. I believe the 1A Line Concentrator presents 24 volts; I am not certain what the digital "SLC" units present as a local loop voltage. > How would I go about getting NY Tel. to fix this? They usually are unwilling > to listen to any problems dealing with data equipment. Sorry, but you gotta problem if all you are paying for is residential service. You could _try_ to talk the telephone company into giving you a metallic pair, but they are not obligated to do so. Your only guaranteed solution is to request a business line with the specific representation that it will be used for data transmission. This will cost you more money, but the charge won't really be absurd if you are making serious use of data transmission. ==> Larry Lippman @ Recognition Research Corp., Clarence, New York ==> UUCP: {allegra|decvax|rocksanne|rocksvax|watmath}!sunybcs!kitty!larry ==> VOICE: 716/688-1231 {hplabs|ihnp4|seismo}!/ ==> FAX: 716/741-9635 {G1,G2,G3} "Have you hugged your cat today?"
w8sdz@brl-smoke.ARPA (Keith B. Petersen ) (08/13/86)
If your modem line is noisy when you try to use it for voice, call the phone company and complain. You have a right to normal volume voice calls with no noise. Don't mention the modem. -- Keith Petersen