rjd@occrsh.ATT.COM (06/16/88)
::What is the difference between a dial phone and a pushbutton phone. :: ::Is it the signal that is sent to indicate a certain number? :: ::And why is it more expensive to use a pushbutton phone? A dial phone uses pulse dialing, which is the method whereby the phone uses a timed series of on/off/on hook pulses to send the number to the phone switch (you can do the same thing by pushing the on-hook button in the proper pattern). A pushbutton phone can be either of the two methods of touch-tone or pulse dialing. If it uses pulse dialing (as most cheaper ones do), then the phone company does not charge any more. If it uses touch-tone, the phone transmits a mixture of two tones for each number (in practice, it happens to be one tone for the column and one for the row). The only reason it costs more is because the phone company wants to charge more. The equipment is newer than the old pulse-dialing decoding, so perhaps they are trying to re-coup the upgrade investment, but the equipment to decode touch-tone is actually cheaper, I hear, than the pulse-dialing decoding equipment. Randy
bobw@wdl1.UUCP (Robert Lee Wilson Jr.) (06/17/88)
The difference in the transmitted signal is considerable: A rotary dial phone (and some electronic push-button phones in a mode which imitates the rotary dialer) just open the line intermittently, once if you dial 1, twice for 2, ... ten times for 0. There are specifications for how long the line is open and the space between pulses: Mechanical dials have a governor mechanism which sets the rate at which the dial returns, and the switch contacts open and close the line during the return rotation. A touch-tone phone sends a pair of tones for each digit. I don't recall the exact frequencies, but there are two bands, each with several frequencies to choose. Each row on the keypad determines a tone from one group and each column determines a tone from the other, so that each key has a unique pair of tones. The spec here is (I assume from observation, i.e. I haven't read it) just a minimum duration, perhaps with some requirement on maximum skew in start/stop times between the tones of a pair: After all the system doesn't seem to care how long you hold the button beyond some minimum, and the tones _are_ generated for as long as you hold the button. Original touch tone phones had discrete transistors and LC tone generator circuits switched by a matrix of contacts corresponding directly to the rows and columns. The simultaneity of the two contacts for a key couldn't have been too great: That's why I assumed above there was no terribly strict spec for skew. Decoding the rotary at the switching office was traditionally done by a special stepping switch, and the 'phone companies had enormous amounts invested in that kind of technology. When touch tone capability was first added to any given exchange, new switching gear had to be added. It made sense, perhaps, to charge extra for the users of that gear. I don't see any reason now for a premium, and I don't recall that I pay any such to PacTel. Presumably every line (after some electronic conditioning) just goes to some specialized IC which is stamped out in enormous volume, can handle both kinds of inputs, and costs almost nothing compared to the labor costs of installing connections, etc. I would be interested if anyone does know of a reason for a differential cost at this stage... Bob Wilson (Disclaimer: As usual, my company wouldn't back up my opinions if they even knew what they were!)
larry@kitty.UUCP (Larry Lippman) (06/17/88)
In article <3310002@wdl1.UUCP>, bobw@wdl1.UUCP (Robert Lee Wilson Jr.) writes: > A rotary dial phone (and some electronic push-button phones in a mode > which imitates the rotary dialer) just open the line intermittently, once > if you dial 1, twice for 2, ... ten times for 0. There are specifications > for how long the line is open and the space between pulses: Mechanical > dials have a governor mechanism which sets the rate at which the dial > returns, and the switch contacts open and close the line during the return > rotation. The "open" specification is usually expressed in "percent break", and is nominally 60% break for most electromechanical switches; i.e., a rotary dial has a normally-CLOSED pulsing contact which opens for 60% of the intradigital pulsing interval. The "speed" specification for normal subscriber telephone applications is nominal 10 pulses/sec. This means that the intradigital pulsing interval is 100 ms, with an open of 60 ms. Therefore, dialing a "1" is equivalent to one line open of 60 ms; dialing a "2" is a 60 ms open, a 40 ms closure, and another 60 ms open; etc. For some PBX and Dial Service Assistance (operator) applications, there are "high speed" dials which run at 20 pulses/sec. These are now pretty much obsolete, however. > A touch-tone phone sends a pair of tones for each digit. I don't recall > the exact frequencies, but there are two bands, each with several > frequencies to choose. Each row on the keypad determines a tone from one > group and each column determines a tone from the other, so that each key > has a unique pair of tones. The spec here is (I assume from observation, > i.e. I haven't read it) just a minimum duration, perhaps with some > ... Touch-tone (which used to be a trademark of AT&T) is more properly called dual-tone multifrequency (DTMF) dialing. Tones are divided into a "low group" (697, 770, 852 and 941 Hz) and a "high group" (1209, 1336, 1477 and 1633 Hz). A digit consists of one frequency from the low group and one frequency from the high group (dual-tone :-) ). There are obviously 16 digit-combinations, but most telephones have only 12 such combinations (0-9, * and #); some VERY old telephones did not even have the * or # keys. The other four digits are used in special applications, most notably AUTOVON (they are usually used to assign a "priority" to calls). Normal central office dial registers do not respond to these other four digits. Most DTMF dial registers in central offices and PBX's will respond to DTMF signaling at the rate of 10 digits/sec, with each tone being present for at least 50 ms, and with an interdigital interval of at least 35 ms. The actual low and high group DTMF frequencies may seem to be a bizarre choice. In fact, they were carefully chosen by Bell Labs to minimize harmonic interference, and to be _least_ likely to be spoofed by speech. > Decoding the rotary at the switching office was traditionally done by a > special stepping switch, and the 'phone companies had enormous amounts > invested in that kind of technology. When touch tone capability was first > added to any given exchange, new switching gear had to be added. It made > sense, perhaps, to charge extra for the users of that gear. I don't see > any reason now for a premium, and I don't recall that I pay any such to > PacTel. Presumably every line (after some electronic conditioning) just > goes to some specialized IC which is stamped out in enormous volume, can > handle both kinds of inputs, and costs almost nothing compared to the > labor costs of installing connections, etc. > > I would be interested if anyone does know of a reason for a differential > cost at this stage... I agree! Additional charges for DTMF service should be abolished! <> Larry Lippman @ Recognition Research Corp., Clarence, New York <> UUCP: {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> VOICE: 716/688-1231 {hplabs|ihnp4|mtune|utzoo|uunet}!/ <> FAX: 716/741-9635 {G1,G2,G3 modes} "Have you hugged your cat today?"
raoul@eplunix.UUCP (Ignacio Nico Garcia) (06/17/88)
The reason it costs more is that the new switching system that uses the tone dialing costs more to install. The old system paid for itself decades ago, but replacing the old switches and wiring, especially with the extra services people expect and demand now, is a new capital expense. It is being spread out over the next generation of phone service, but it still costs an arm and a leg to install that much stuff. An additional major expense is keeping it retro-fitted. The new system has to work perfectly with old equipment still in place. This is why many businesses find it cheaper to rip out their entire old phone system and replace their phone system from the ground up, paying Ma Bell only for their outside lines. That the entire system didn't break down years ago, and that the standards have changed so little that my fifty-year old antique phone only needed a new cord to work properly, is a credit to Ma Bell's engineers and foresight when they installed it. It is also why they have been so reluctant to alter their standards: they are afraid of having to upgrade everything every two years, instead of the stability they have enjoyed in the past. The switchovers to optic cables and microwave uplinks could have happened years ago. Ma Bell waited until the standards were settled in that arena as strongly as they were in the electrical one before installing anything, though. For anyone in the Boston area who is interested in these technologies, I would audit the 6.311 course at MIT, which goes into depth on the telephone system. raoul
kamath@reed.UUCP (Sean Kamath) (06/18/88)
In article <131500002@occrsh.ATT.COM> rjd@occrsh.ATT.COM writes: > > The only >reason it costs more is because the phone company wants to charge more. >The equipment is newer than the old pulse-dialing decoding, so perhaps they >are trying to re-coup the upgrade investment, but the equipment to decode >touch-tone is actually cheaper, I hear, than the pulse-dialing decoding >equipment. > >Randy Not any more. We got a note on our phone bill about seven months ago saying they were removing the whopping $.55 a month charge for touch-tone (tm) because the FCC decided they couldn't charge more for it. I almost couldn't believe it when I saw it...The FCC trying to save *me* money? Ha. Sean Kamath -- UUCP: {decvax allegra ucbcad ucbvax hplabs ihnp4}!tektronix!reed!kamath CSNET: reed!kamath@Tektronix.CSNET || BITNET: reed!kamath@PSUVAX1.BITNET ARPA: reed!kamath@PSUVAX1.CS.PSU.EDU US Snail: 3934 SE Boise, Portland, OR 97202-3126 (I hate 4 line .sigs!)
markz@ssc.UUCP (Mark Zenier) (06/19/88)
In article <2565@kitty.UUCP>, larry@kitty.UUCP (Larry Lippman) writes: > ... > I agree! Additional charges for DTMF service should be abolished! As of May 2, Pacific Northwest Bell, " a US West Company" dropped the $0.50 a month charge for tone dialing for residential customers. I bet they'll stick me with a healthy one time charge to get it turned back on, though. Mark Zenier Holder of the Cliff Claven chair at the school of uunet!pilchuck!ssc!markz Unsubstantiated Opinion
henry@utzoo.uucp (Henry Spencer) (06/20/88)
> ... the equipment to decode > touch-tone is actually cheaper, I hear, than the pulse-dialing decoding > equipment. In fact, this was the major motive behind tone dialing. It's not so much that the equipment is cheaper, as that it is tied up for a shorter period of time because tone dialing is quicker. This means that a phone exchange can get by with fewer dialing-receivers (don't remember the proper buzzword for them) than it would need for pulse dialing. (No, your line is not connected to one at all times -- that's why you get a dial tone, to tell you that the exchange has noticed you lifting the phone and has connected one to your line. This situation may be changing in the very latest LSI-based exchanges, but the traditional designs have an absolute minimum of dedicated equipment per line.) The phone companies originally charged more for tone dialing because the new equipment had to be installed and it seemed reasonable that the folks who wanted it should help pay for it. Now that tone dialing is nearly universal, they really should start charging extra for *pulse* dialing, since its lower speed ties up the equipment longer. However, the Bell empire is under great pressure to hold down the price of the most basic form of phone service, and this means charging extra for absolutely everything else to make ends meet. Today's political environment discourages short-term upheavals even when they would lead to long-term savings. -- Man is the best computer we can | Henry Spencer @ U of Toronto Zoology put aboard a spacecraft. --Von Braun | {ihnp4,decvax,uunet!mnetor}!utzoo!henry
awpaeth@watcgl.waterloo.edu (Alan Wm Paeth) (06/20/88)
> ... Original touch tone phones had discrete transistors >and LC tone generator circuits switched by a matrix of contacts >corresponding directly to the rows and columns... Original touch tone phones had *ONE* transistor -- there is nothing prohibiting an oscillator's generating two simultaneous frequencies, and Bell's introduction of solid state electronics into the consumer phone followed the KISS "keep it simple, stupid" philosophy to its extreme. Phone system design in North America has always followed this design principle -- clever circuits and architecture minimize the the "per circuit" complexity of each line, thereby allowing a system of around 10^8 telephones to be maintained by a huge decentralized pool of minimally trained maintainers ("the phone men"). As a second example, consider that a consumer phone line (one twisted pair) allows simultaneous (full duplex) conversation, yet each speaker hears his own voice in the headset at a much lower volume than the remote sender, all this done without the benefit of digital, let alone solid state components. Moreover, each phone contains no power supply -- the two leads to the exchange supply power, bidirectional data and also allow for remote ringing, yet each set contains only a handful of 1950's parts [but no vacuum tubes :-)]. I don't think most folks could draw the circuit off the tops of their heads. /Alan Paeth Computer Graphics Laboratory University of Waterloo
neals@tekigm2.TEK.COM (Neal Sedell) (06/21/88)
In article <1274@ssc.UUCP> markz@ssc.UUCP (Mark Zenier) writes: ... >As of May 2, Pacific Northwest Bell, " a US West Company" dropped the >$0.50 a month charge for tone dialing for residential customers. I bet ... Now, if only they would drop the charge for an unlisted/unpublished number that whoever calls directory assistance PAYS FOR ANYWAY!!! Talk about shady practices by military contractors... Neal Sedell disclaimer: I am a PNB customer and dislike having to pay to not be harassed by some bozo's unsolicited solitication every other day!
maxwell@ablnc.ATT.COM (Robert Maxwell) (06/21/88)
I don't remember the details, and I don't want to try to look them up, but one of the reasons there is a charge is tariffs. Whether or not it costs the phone company extra to provide the service, if they cannot offer it to all their customers at the same time, they need to tariff it as an extra cost item. When they first offered Touch-Tone, it was costing them extra to provide the equipment for it, especially if they had to retrofit existing step-by-step or crossbar offices for it. The extra charge will be with around in individual service areas at least until the service can be offered to all subscribers using the equipment already in place. By the same reasoning, the day may come when pulse dialing is an extra cost service. -- ----------------------------------------------------------------------------- R. M. Maxwell AT&T IMS | I speak for nobody- Maitland, FL ablnc!jezebel!bob | not even myself. -----------------------------------------------------------------------------
markz@ssc.UUCP (Mark Zenier) (06/22/88)
In article <531@ablnc.ATT.COM>, maxwell@ablnc.ATT.COM (Robert Maxwell) writes: > ... > By the same reasoning, the day may come when pulse dialing is an extra > cost service. I heard a rumor that it is a legal requirement that you can get the operator on a phone with no dial by tapping the hookswitch 10 times. That would require TPC to provide pulse dialing. Is this so? Mark Zenier Holder of the Cliff Claven chair at the school of uunet!pilchuck!ssc!markz Unsubstantiated Opinion
wte@ncrcae.Columbia.NCR.COM (Bill Eason) (06/23/88)
In article <4937@watcgl.waterloo.edu> awpaeth@watcgl.waterloo.edu (Alan Wm Paeth) writes: >Original touch tone phones had *ONE* transistor -- there is nothing >prohibiting an oscillator's generating two simultaneous frequencies... How? >As a second example, consider that a consumer phone line (one twisted pair) >allows simultaneous (full duplex) conversation, yet each speaker hears his >own voice in the headset at a much lower volume than the remote sender, all >this done without the benefit of digital, let alone solid state components. >Moreover, each phone contains no power supply -- the two leads to the exchange >supply power, bidirectional data and also allow for remote ringing, yet each >set contains only a handful of 1950's parts [but no vacuum tubes :-)]. >I don't think most folks could draw the circuit off the tops of their heads. Can you? Not to be sarcastic, just curious about how it's done. How hard would it be to make the support electronics (power supply, etc.) for your own private in-house telephone setup? Disregard touch tone decoding and call routing, I guess... just the duplex/ringing/volume stuff. > /Alan Paeth > Computer Graphics Laboratory > University of Waterloo (I never can remember when my .signature is automatically included...) Bill Eason (803) 791-6419 ...!ucbvax!sdcsvax!ncr-sd!ncrcae!sauron!wte NCR Corporation ...!rutgers!mcnc!ece-csc!ncrcae!sauron!wte E & M Columbia 3325 Platt Springs Rd. West Columbia, SC 29169 -- Bill Eason (803) 791-6419 ...!ucbvax!sdcsvax!ncr-sd!ncrcae!sauron!wte NCR Corporation ...!rutgers!mcnc!ece-csc!ncrcae!sauron!wte E & M Columbia 3325 Platt Springs Rd. West Columbia, SC 29169
dasilva@savax.UUCP (Herbert S. DaSilva) (07/08/88)
In reply to the question: Can anyone see a reason to pay a premium for touch-tone service? I live in Taxachussetts, and in my town, you can just plug a touch tone phone into the wall, and it works. (Even though the phone bill doesn't reflect any special charges for Touch-tone service. This has been the case for the last 6-8 years, before then, I didn't care...:-) Herb