Post by thread:[OT] Telephone use & time calculation

At 18:43 02/08/99 -0500, dave vanhorn wrote: >>in germany they optionally send a billing impulse -- 15kHz, some 10 ms >>duration -- which signifies a certain billing increment. works for all >>billed calls, and is kinda helpful in some situations. but it can mess with >>your modem communication quite a bit if your modem is not prepared and has >>the appropriate filters :) > >You ain't just whistlin 15khz either. That is one HOT tone! it has to be pretty hot, because the system wasn't designed for that bandwidth, so the losses are not precisely calculable and there has to be a pretty big margin. pretty lucky though that it doesn't actually get to the ears :)) >As usual, the americans do it first, the europeans think (argue?) about it >for a while, and come up with a better system.. Witness NTSC. did you have billing tones here once? but better or not -- it might be complicated to fit into the billing system here. germany's billing system is based on those billing units, whereas here carriers are allowed to bill however they like. and as far as europe goes: i think it's a pretty much german only thing; i'm not aware of billing impulses in any other european country. maybe because we're accountants by nature after all? :) ge

Gerhard Is it 15 KHz or 16 KHz ? Here in India, we have 16 KHZ metering pulses. Pailoor Gerhard Fiedler wrote: {Quote hidden}> At 23:13 02/08/99 +1000, Paul B. Webster VK2BZC wrote: > > You can tell when the phone goes "off-hook", when and which tones > are > >dialled, and when it goes back "on-hook". You can´t easily tell when > > >(and if) it is actually answered so you have to make an assumption > that > >it is answered shortly after the *last* tone is dialled, and toll > paid > >until it goes back on hook. > > in germany they optionally send a billing impulse -- 15kHz, some 10 ms > > duration -- which signifies a certain billing increment. works for all > > billed calls, and is kinda helpful in some situations. but it can mess > with > your modem communication quite a bit if your modem is not prepared and > has > the appropriate filters :) > > ge -- Chip Technologies Microchip Design Consultant No. 70, 9th Main Road, Mathikere, Bangalore - 560 054. INDIA Tel : +91-80-3362807 Fax : +91-80-3369451 Email : spam_OUTchiptechTakeThisOuTvsnl.com Webpage : http://business.vsnl.com/chiptech

At 08:25 02/09/99 +0530, Ravi Pailoor wrote: >Is it 15 KHz or 16 KHz ? Here in India, we have 16 KHZ metering pulses. yes, you're right, it's 16kHz in germany as well. and it's gotten slightly confusing there since i left: they opened the long distance carrier market, and since the telcom switches don't transmit billing information, calls using one of the optional carriers (a similar access system as with the 1010257 or so prefixes here in the usa) don't provide the billing pulse. many hotels and other enterprises seem to have troubles adapting to the new situation of the possibility of having calls on the system that don't provide a billing pulse but nevertheless get billed -- probably in the beginning a couple of verrry smart guys got away without paying their phone bill :) FWIW, at www.ct.heise.de/ct/faq/hotline/97/05/hotline9705_15.shtml is a nice suggestion to wire a modem with a filter so that the modem signal goes through the filter but not the phone signal (if you're using a pulse counter in the phone). no other components necessary. ge

Gerhard Fiedler wrote: > yes, you're right, it's 16kHz in Germany as well. and it's gotten > slightly confusing there since I left: they opened the long distance > carrier market, and since the telcom switches don't transmit billing > information, calls using one of the optional carriers (a similar > access system as with the 1010257 or so prefixes here in the usa) > don't provide the billing pulse. Of course they don't, because ... you don't want to be billed for them! Billing pulses are to register charges to your primary (local) carrier. If the others provided these pulses, you'd be paying double! In this country, public phones used to be metered by "flash reversals" which produced a "plop-plop" on the line, but I understand have now been converted to 50 Hz (Mains frequency!) pulses. > many hotels and other enterprises seem to have troubles adapting to > the new situation of the possibility of having calls on the system > that don't provide a billing pulse but nevertheless get billed -- > probably in the beginning a couple of verrry smart guys got away > without paying their phone bill :) They would have to have a "lock" so that only one carrier is used. Administration otherwise would be too complex (though I reckon someone will have a go at this!). > a nice suggestion to wire a modem with a filter so that the modem > signal goes through the filter but not the phone signal (if you're > using a pulse counter in the phone). 16 kHz is so far from the upper line bandwidth (3 kHz or 3.3 kHz) that most modems *should* filter this automatically (DSP anti-alias). > it has to be pretty hot, because the system wasn't designed for that > bandwidth, so the losses are not precisely calculable and there has to > be a pretty big margin. Well, that's not quite so. This signal is injected at the SLIC anyway as it is certainly not carried over the exchange circuits (or are we talking pre-digital systems?). The subscriber line *can* handle that bandwidth because it at least potentially, can be used for higher-grade digital transmission. Or so they're *hoping* for the next century. > pretty lucky though that it doesn't actually get to the ears :)) Wouldn't be noticeable, since most adults are fairly deaf to it! When could *you* last hear the TV set's horizontal scan whine from the other end of the house? It's most certainly filtered out by the telephone receiver. -- Cheers, Paul B.

At 00:21 02/10/99 +1000, Paul B. Webster VK2BZC wrote: >Gerhard Fiedler wrote: > >> yes, you're right, it's 16kHz in Germany as well. and it's gotten >> slightly confusing there since I left: they opened the long distance >> carrier market, and since the telcom switches don't transmit billing >> information, calls using one of the optional carriers (a similar >> access system as with the 1010257 or so prefixes here in the usa) >> don't provide the billing pulse. > > Of course they don't, because ... you don't want to be billed for >them! Billing pulses are to register charges to your primary (local) >carrier. If the others provided these pulses, you'd be paying double! for one, that's apparently different in germany. the calls made through these carriers get billed on the same main bill. and in any case, that's not the issue: even if i got billed by them directly, they still could send the local carrier the billing information (while i'm talking), and i could get the pulses accordingly, without double billing (since the local carrier would know that the billing information came from another carrier, and just put the corresponding pulses on the line without charging me). it's just that the switch protocols don't provide that information, i'm told. this seemed to have been (or maybe still is) a big issue in germany, since a lot of telco equipment and procedures relied on the pulses, and it seems to me that if the switch protocol would make it possible to provide that information, they probably would've designed something to get it done. but i'm no telecom specialist... >> many hotels and other enterprises seem to have troubles adapting to >> the new situation of the possibility of having calls on the system >> that don't provide a billing pulse but nevertheless get billed -- >> probably in the beginning a couple of verrry smart guys got away >> without paying their phone bill :) > > They would have to have a "lock" so that only one carrier is used. >Administration otherwise would be too complex (though I reckon someone >will have a go at this!). yes, that's what they're doing now. it's just that for ages hotel systems had all their billing (and billing equipment) based on the pulses, so this change apparently had quite an impact. >> a nice suggestion to wire a modem with a filter so that the modem >> signal goes through the filter but not the phone signal (if you're >> using a pulse counter in the phone). > > 16 kHz is so far from the upper line bandwidth (3 kHz or 3.3 kHz) >that most modems *should* filter this automatically (DSP anti-alias). i can tell you from my own experience that this is not true. at least during the time i used imported modems in germany (that was pre-v.34, 10 to 8 years ago), most of them got heavy hiccups from the pulses (up to loosing carrier without being able to reconnect -- the zyxel modems, with their proprietary 19k2 protocol when everybody else was happy to get 14k4, were particularily difficult), which could be solved by a filter -- that's where those suggestions came from. >> it has to be pretty hot, because the system wasn't designed for that >> bandwidth, so the losses are not precisely calculable and there has to >> be a pretty big margin. > > Well, that's not quite so. This signal is injected at the SLIC anyway >as it is certainly not carried over the exchange circuits (or are we >talking pre-digital systems?). probably, at least historically. i think the billing pulse predates all-digital systems; they may be it by now, but the standard probably has been desgined to work on analog systems as well (or only). >The subscriber line *can* handle that >bandwidth because it at least potentially, can be used for higher-grade >digital transmission. Or so they're *hoping* for the next century. is that true? i mean, i figure that =some= lines are good enough, but that's not reliable. especially in countries like australia and the usa with the long distances in some places, there seem to be a number of remote subscriber lines which i assume would damp a 16kHz pulse quite considerably. do you think you can go with, say, 12kbaud (not 12kbps! this is of course possible) over all subscriber lines? >> pretty lucky though that it doesn't actually get to the ears :)) > > Wouldn't be noticeable, since most adults are fairly deaf to it! When >could *you* last hear the TV set's horizontal scan whine from the other >end of the house? not from the other end... but i uauslly don't hold the phone receiver at the other end of the house, either :) >It's most certainly filtered out by the telephone receiver. i guess i'm in the age by now where my audio bandwidth is getting smaller; i haven't tested it in a while but i'm still happy that the receiver isn't a piezo or something which wakes up at 16kHz for real activity :) ge

I read a discussion of metering pulses on a Usenet news group once and it seems that several versions of the system are or were used. Each pulse stood for one billing unit and each billing unit always cost the same amount of local money, but the trick was that the billing agent would change the pulse rate to deliver more pulses in a given period of time for a call that cost more per minute. If each billing unit was, say worth $0.10 and the call cost $0.30 per minute, you would get hit with a pulse every 20 seconds. The pulses were supposed to be inaudible. Since a modern telephone line is a balanced pair, the billing pulses were fed via the common mode to both wires and theoretically did not show up as a signal between the two wires. One had to read between one conductor and Earth to receive the 50-HZ bursts. I think the older systems actually had a small relay or solenoid-driven counter to allow one to see how much money was drip-dripping away while they were talking. Obviously, the German system is one of the variations on this theme, but the 16-KHZ pulses still stand for some preset unit of cost and the rate is simply sped up or slowed down depending upon the per-minute cost of the call. Martin McCormick WB5AGZ Stillwater, OK OSU Center for Computing and Information Services Data Communications Group