lagasse@biomed.UUCP (Robert C. Lagasse) (07/26/85)
Does anyone have any idea how much a telephone company "leased-line" costs? Is it so much per mile? ( A leased line is a pair of wires from one point such as a business or residance to another site such as a repeater site or another building). These are usually used with buglar alarm systems and commercial broadcast radio "remotes" and I believe consist of nothing more than a pair of wires from one site, to the phone company central office , then to the other site with no switching or electronic intervention in between. ( Does anybody have any ideas how many junctions the installer of such a line has to make? I figure a minimun of three. One at the pole at one end, one that he must call into a central ofiice to have someone make between two big fat trunk cables, and then another at the pole at the other end). I believe you can put a battery of, say, 10V at one site and measure the battery voltage at the other, minus the voltage drop due to connections and distance. By the way, does anyone know?: a) the maximum allowed voltage on a leased line b) how many volts/mile is usually lost, and c) maximum allowable current (do they fuse it somewhere?). I called the phone company and got the royal run-around. I tried to explain what I wanted but was told of auto-ring circuits like the taxi phones use (how much do they charge for those/month). As soon as I mentioned that it would be for ham-radio remote control and also possibly burglar alarm monitoring, I was referred to the "mobile-phone" group which deal with mobile phone companies (probably that cellular garbage) and they told me their lines cost $24.50/month and then an additional fee for each minute of "air-time". I then tried calling back the original office and re-explained that it would be like a burglar alarm line, was then asked if it was for voice, I was puzzled and said no, and was then told that burglar alarm lines run ONLY to the police station and could not go between residences.(when she asked me if it would be used for voice, it made me wonder if they sell different kinds of lines , like, voice-quality, and not voice-quality?? What good is a non-voice quality line anyway????) I then tried to explain that all I wanted was a pair of wires from point A to point B but then she asked, " what kind of jack do you need, an RJ-11C?" As you can see, I could not get past the non-technical salespeople. What is the OFFICIAL name for this kind of line? If there are any phone company gurus out there, H E L P! Thank you for any and all answers. Bob Lagasse N 1 A L G
connolly@steinmetz.UUCP (C. Ian Connolly) (07/27/85)
> ... (when she asked me if it would be used for voice, it made me > wonder if they sell different kinds of lines , like, voice-quality, and not > voice-quality?? What good is a non-voice quality line anyway????) > Bob Lagasse N 1 A L G They were probably wondering if you wanted voice quality or data quality. Data quality lines are less noisy than voice quality. It sounds like you want a data-quality leased line. -- C. Ian Connolly, WA2IFI - USENET: ...edison!steinmetz!connolly , , ARPANET: connolly@ge-crd An rud a bhionn, bionn.
hoffman@pitt.UUCP (Bob Hoffman) (07/29/85)
The name you'll want to use when dealing with the telco is
"Local Area Data Channel", or "Local Area Data Service". We
usually just call them LADS lines. You will probably want to
get a publication from the telco called "Data Communications
using Local Area Data Channels". Its number is PUB 41028, dated
June 1979. This used to be called a "Bell System Technical Reference",
but is probably something else since the divestiture. All of the
technical questions you raised are answered in this publication.
If you want end-to-end DC continuity, you must ask for it specifically.
As for cost, the ones we have that connect buildings on campus cost
$38 per month per pair ($76/month for a 4-wire DC line). Using
Bo-Sherrell M1 short-haul modems (actually differential DC line
drivers), we can get no more than 2400 baud on them.
I hope this helps.
---Bob.
--
Bob Hoffman, N3CVL {allegra, bellcore, cadre, idis, psuvax1}!pitt!hoffman
Pitt Computer Science hoffman%pitt@csnet-relaylarry@kitty.UUCP (Larry Lippman) (07/30/85)
> Does anyone have any idea how much a telephone company "leased-line" > costs? Is it so much per mile? ... Having battled with Ma Bell (or what *used* to be Ma Bell) for a number of years on leased lines for process control and telemetering purposes, I'll try to give you a brief summary of what you can and cannot do. First of all, there may be some variations of what I have to say, depending upon the tariffs of your local telephone company. What I am saying is correct for NY Telephone, however. Charges are based upon where the two leased line termination points fall with respect to telco-defined central office boundaries. There boundaries generally bear little resemblence to city/town/village/county boundaries. If the two points fall within the same central office district, then the charges consist of central office loop charges - one for point A to the CO, and one for point B to the CO. In addition, there are local wiring and jack charges for each end. The average charge for a leased line having both points within the same central office in upstate New York is around $ 35.00/month, with an installation charge of around $ 300.00. Don't forget - this charge could well be different in your area. If the two points are in different CO's, you will pay the airline mileage between the two CO's in addition to the central office loop and local wiring/jack charges If the two termination points are only 1,000 feet apart but in different CO districts, you will *still* pay the airline mileage! This is referred to interexchange mileage (IXC). In upstate New York this is around $ 24.00 per mile per month for an IXC of less than 12 miles. The rate decreases for over 12 miles. Let's assume your leased line is in the same CO district. What do you get for your 35 bucks a month? You get a pair of wires have a DC loop resistance of no more than 1,000 ohms and an attenuation at 1 kHz of no more than 5.5 dB. If your total *loop* distance is greater than 2 miles you will most likely have a pair with loading on it, which will automatically limit your high frequency response to 3 kHz. You should not assume an upper frequency response of greater than 3 kHz anyhow. In general, you cannot apply tone signalling to the leased pair in excess of 0 dBm. You cannot exceed 135 volts from either conductor to ground, or 270 volts from conductor to conductor. You cannot exceed 150 milliamperes in loop current. Any circuit which you connect to the leased line must be longitudinally balanced. You can request a line impedance of 600 or 900 ohms; whether the circuit is actually engineered for the requested impedance is another matter. If there is significant distance between the two terminal points, the telco may provide (as part of the expense) a repeater amplifier so that they will meet the 5.5 dB transmission requirement. This repeater will be of either a negative-impedance E-type, or of a hybrid V-type. If there is a repeater provided, you MUST maintain your requested 600 or 900 ohm impedance at BOTH ends or the circuit may `sing`; this is your responsibility, and not the telco's. Either of the above repeaters will pass DC signalling and will of course provide the same gain in both directions. Unbalanced DC currents may also saturate the transformers in the repeaters and cause them to sing. In general, your equipment should work on a 1,000 ohm loop. While you can request a lower loop resistance, you might have to pay extra for it, or it simply may be unavailable for the particular circuit. If your circuit runs between two central offices, you cannot get DC continuity from the telco, and you will have to use tone signalling, all of which will have to be inband (300 to 3,000 Hz). There is a type of DC signalling called E&M signalling which is availavle at extra cost. In simple terms, E&M signalling will give you a contact closure in each direction at a rate not to exceed 20 Hz. The telco installs additional equipment to facilitate the E&M signalling function - which is *their* responsibility. You must be able to source a current-limited -48 volts DC in order to interface with the E&M signalling equipment. If your IXC is greater than 12 miles, you are entitled to get a four-wire termination if you so choose at no extra cost. Four-wire circuits for less than 12 miles IXC cost twice as much as a two-wire circuit. To order your circuit you should request a "Radio Tie Line" to make things simple for the usual idiots at the business office. They will no doubt refer you to a specialized salesperson who handles leased-lines, who will send you an engineering form to fill out where you describe your terminal equipment and your desired circuit specifications. You will also have to certify on this form that you will not exceed any pre-defined circuit limits (like voltage, current, etc). The limits really *DO* have to be adhered to so as not to cause interference to other services in the same cable, or cause harm to the network or telco craftspersons. Chances are you will find the cost of *any* leased-line prohibitive for amateur radio use, but I thought I would at least take some mystery out of the world of leased-lines. Larry Lippman Recognition Research Corp. Clarence, New York UUCP {decvax,dual,rocksanne,rocksvax,watmath}!sunybcs!kitty!larry {rice,shell}!baylor!kitty!larry syr!buf!kitty!larry VOICE 716/741-9185 TELEX {via WUI} 69-71461 answerback: ELGECOMCLR "Have you hugged your cat today?"
larry@kitty.UUCP (Larry Lippman) (07/31/85)
> > ... (when she asked me if it would be used for voice, it made me > > wonder if they sell different kinds of lines , like, voice-quality, and not > > voice-quality?? What good is a non-voice quality line anyway????) > > Bob Lagasse N 1 A L G > > They were probably wondering if you wanted voice quality or data quality. > Data quality lines are less noisy than voice quality. It sounds like you > want a data-quality leased line. There are several basic categories of leased lines: (1) SIGNAL GRADE lines provide metallic continuity and will generally provide a frequency response up to 30 Hz. There is absolutely no attempt at loading or other circuit design for voice frequencies. Nothing prevents voice frequency use if the loop is short and within the same central office. (2) TELEGRAPH GRADE lines provide neutral or polar signalling for tty's, and are available up to 150 baud. Voice transmission is not possible because all you get are signalling leads from a telco interface. (3) VOICE GRADE lines give you a bandwidth of 300 to 3,000 Hz with DC continuity if within the same central office. E&M signalling is available if more than one central office is involved, but you won't get actual DC continuity any more. (4) OFF-PREMISES EXTENSION lines giving you voice frequency range with DC and ringing transmission *specifically* intended for use with PBX's. (5) RINGDOWN TIE LINES like taxicabs, hotels, etc. use. You pick up a non-dial telephone at one end and a similar telephone rings at the other end. (6) DATA GRADE lines still give you only 300 to 3,000 Hz frequency response with *no* DC signalling; however, the lines are carefully designed for flat frequency response (i.e., equalized), low noise, low envelope delay, low phase jitter, etc. There are various categories of the above parameters called 'conditioning', with typical grades of C1, C2, and C3 conditioning. The higher numbers give better quality for more $$$. Conditioning becomes critical when data circuits must run through carrier equipment. (7) WIDEBAND DATA lines available in typical bandwidths of 48 kHz and 256 kHz. These lines are so expensive it's unreal. (8) RADIO PROGRAM lines typically provide *one-way* service for radio stations, and are available equalized for 5 Khz and 15 kHz bandwidth. (9) VIDEO CIRCUITS where available are gen-u-wine coaxial cable or telco microwave link with a 6 MHz bandwidth. These lines are *so* expensive you don't even want to ask... (10) DIGITAL DATA SERVICE is pretty much an AT&T offering where you can get data circuits with data sets for speeds from 2,400 baud to 1.5 Mbits/sec. There are all sorts of variations of the above, like multi-point lines, special burglar alarm lines (series circuits), telex/twx lines, etc. And then if you want a *real* laugh, ask your telephone company for Picturephone (tm) service... :-) to AT&T Larry Lippman Recognition Research Corp. Clarence, New York UUCP {decvax,dual,rocksanne,rocksvax,watmath}!sunybcs!kitty!larry {rice,shell}!baylor!kitty!larry syr!buf!kitty!larry VOICE 716/741-9185 TELEX {via WUI} 69-71461 answerback: ELGECOMCLR "Have you hugged your cat today?"
hes@ecsvax.UUCP (Henry Schaffer) (07/31/85)
We rent copper telco pairs on campus, and use two pairs per terminal for a switched data network. We use a home-made line driver, and routinely run at 9600 bps, with 19,200 bps appearing to work, as well. Our longest run is probably 1-2 miles. If you can't run copper pairs that fast you may have loaded lines. --henry schaffer
stekas@hou2g.UUCP (J.STEKAS) (08/03/85)
> We ... routinely run at 9600 bps ... Our longest run is probably 1-2 miles. > If you can't run copper pairs that fast you may have loaded lines. I recall reading that Telcos will, on occaision, resort to filters and other devices to prevent a line from grossly exceeding specifications. Apparently, people needing short voice grade private lines were ordering alarm/telemetry lines and using them for voice. Maybe they got tired of complaints about "voice quality". Jim - NJ2F