Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/5/84; site kitty.UUCP Path: utzoo!watmath!sunybcs!kitty!larry From: larry@kitty.UUCP (Larry Lippman) Newsgroups: net.ham-radio Subject: Re: leased lines Message-ID: <176@kitty.UUCP> Date: Tue, 30-Jul-85 01:18:36 EDT Article-I.D.: kitty.176 Posted: Tue Jul 30 01:18:36 1985 Date-Received: Wed, 31-Jul-85 02:20:07 EDT References: <103@biomed.UUCP> Organization: Recognition Research Corp., Clarence, NY Lines: 86 > 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?"