Only on longer lines where they need that much voltage to ensure enough current to power the remote equipment. With the phone operating this should drop considerably. Same with HDSL lines but not ADSL where the equipment is not powered over the line as the phone service is still as was.
Oh yes it can, I used to live in Denmark but moved to UK three years ago, and in DK i had a SDSL line at 512kbps (Symetric = 512kbps upstream /
512kbps downstream) ontop of a ISDN2 line, so yes it can be done, its just BT who is being a few years behind because I got this line 7 years ago from TeleDenmark...I don't know what equipment they use over here, but in DK the equipment used could support anything upto 8Mpbs agregated, ie. any combination of uplinks / downlinks ontop of whatever phone line you may have (within line length / qualility of line restrictions) that could be ISDN, POTS or just the lines (ie. no connection to the phonenetwork at all)
Until we put some pressure on BT nothing wil change! (comming from a cheased off ex ISDN costumer who had to convert back to POTS to get his ADSL installed)
/Morten
They use two lines, radio signals to you and ground back. Without a common ground / return you can't communicate, ie. you need to be able to detect a signal as a difference to the return lines / ground lines...
/Morten
I was only suggesting that this was the source of the "90V" that TNP was thining of.
Thinking on it, it comes from the old BBC telephone ringers - used to ring an 'in shot' phone in say a studio drama. They had selectable 17/25 Hz but IIRC could do UK, 'continental' and US type rings.
Which is why radios don't work in aircraft.
No connection to ground :-)
Hmmm, good point :-)
But for non radio wave comminication you still need two lines...
/Morten
I suspect Dave knows that other PTTs manage it, hence his comment about "according to BT", I seem to remember that in in Germany they do ISDN+DSL too, can't remember if there is/was a speed penalty to pay though ...
Ditto :-(
Would be so much easier to link ISDN into PC running asterisk that messing about with analogue FXO card (2 lines, no echo from impedance mismatch, CLI and multiple numbers)
"Morten" wrote | But for non radio wave comminication you still need two lines...
No you don't.
Piece of string between two cocoa tins is only one line and works fine.
Until it gets soggy.
Probably why there were never any 0898 services on cocoa-tin phones. Nor on speaking-tubes neither.
Owain
Quite, I'm glad some one reads usenet posts properly. B-)
Yes, they do have ISDN+DSL in Germany, and no speed penalty...
Thomas Prufer
It can be done, and there is a speed penalty, especially upstream, as all the lower bandwidth is used for ISDN. But the general view back when the system was being designed was this complicated matters so leave it out. Germany had already made a major committment to ISDN in the home and so had little choice but to implement it.
True SDSL does not work on top of POTS, ISDN or anything as it has low frequency components. It is more likely that the Danish ISDN data was instead decoded and sent over the SDSL link, then recoded into an ISDN link at the other line.
The BT ADSL equipment is the same as elsewhere in the world and so could run at 8 Mbps for short lines only. However most countries don't have a universal service obligation and so this has really held BT back to increasing speeds slowly in constant discussion with OFTEL/OFCOM. Even when
512kbps was introduced the howls from people on lines so long that could barely support audio still had MPs asking questions in Parliament.
Ground isn't needed. But yes there are are two signals from an aerial though, the E part and the M part. Each forms a carrier for the other.
On Tue, 21 Dec 2004 09:29:24 -0000, "Morten" strung together this:
Moist string and rusty tin cans mostly.
There was no coding / decoding of ISDN data over the SDSL, the ISDn worked just fine with / without the SDSL modem inline, there was a few of the lower channels that were missing, so the full available bandwidth was a few channels short, but still way more that the committed upstream / downstream they sold you, so it didn't matter.
It wasn't until recently they started to sell more than 2Mbps lines but they normally only works on shorter lines...
In Denmark it was tough luck if the wire that TeleDK supplied didn't work for ADSl / SDSL, as long as they could get a POTS / ISDN signal through the line their obligation stopped. I spoke to one of their technicians once and he said that it was common for them to convert a faulty POTS line to ISDN for a few days, that would burn out any loose connections and either open the line completely (making it much easier for them to find the blown connection via time / domain analysis) or fixing the line.
Incidently there was far more problems with POTS that ISDN, the only downside of ISDN was that they charged you an arm and your soul to pay for it...
And they supplied a ISDN2 connection with full commandset, and not a bastardised ISDN like the one they flunk here in UK...
/Morten
No, you really sort of don't, byt it helps :-)
AC power can be entirely communicated by capacitors which are open circuit to DC.
But teh exact specifications are non trivial.
Just a quick update. Had BT round two days in a row sorting out new line
- ended up replacing yards of cable - and they confirm that ADSL often 'works' when baseband phone doesn't.
Now I have to wait for new phone to come up in 'ADSL compliant' register before ordering broadband.
It is taking WEEKS to get teh HS stiff...
shouldn't you see a doctor about that?
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