Re: DSL Speed

Robert B>> >>> At the farm, it seems to be the wire that limited my dialups to 46k

>>> when I got 52k in town. >> Yes, and no. The particular _type_of_signaling_used_ over that wire >> was limited by that wire to 46k. >>> If the wire wouldn't carry more than 46k, it wouldn't matter what >>> the telco did at their end. >> *NOT* exclusively a 'wire' limitation. Also a limitation of the >> signalling technology employed. the distributed capacitance of the >> wire was such that it 'blurred' the signal such that reconstruction of >> the original waveform =after= the *VOICE*GRADE* analog-to-digital >> conversion in the CO switch lost the 'fidelity' required for the >> higher data rate. >>> I wonder how a DSL signal can carry 1.5M through those mile of wire. >> DSL uses a different 'signalling technology' for sending the data down >> the wire. >> The DSL signal does _not_ go through those 'voice-grade' >> analog-to-digital converters that PSTN calls do. the signal is >> isolated before that point, and dumped into a totally _different_ kind >> of receiver. > Is DSL modulated into some sort of analog signal? It's hard to imagine > carrying hig-frequency digital pulses on copper telephone lines.

Get thee to a _library_. they have entire books on the subject.

> DSL _does_ suffer 'performance losses', as the wire length gets >> greater. The degree of degradation is considerably worse than with >> POTS modems. E.g., at 1,000' from the C.O. you may be able to get >> several megabits/sec. at 15000 ft, you'll be lucky to get 256k. At >> 18,000 ft, even 144kbit/sec is iffy. Beyond 25,000 ft, "forget it" >> applies -- an analog POTS modem is higher performance. > The farm appears to be 35,000 feet from the central office. My browser > often shows downloads faster than 1.5 Mb/s (150kB/s).

That which "appears" to be the situation is often not the reality.

There may be a 'remote node' outlying from where you "think" the central office is. The DSLAM equipment can be located there.

>>>> I have trouble understanding on the phone, and I often resort to >>>>> the phonetic alphabet to be understood. I think the problem may be >>>>> more in the typical quality of phones than in bandwidth. You could >>>>> have broadcast quality microphones and loudspeakers and it will >>>>> still sound like a telephone because of the limited bandwidth. >>>>> Since bandwidth is limited, telephone components aren't high >>>>> fidelity as it would be a waste to make them so. (I believe the >>>>> modern "K" handset is clearer than the older "G" handset.) >>> Military AM and SSB are limited to 300-3000 Hz. Shortwave radios can >>> be filtered that way for tuning and difficult conditions. Speach >>> comes across pretty clearly. If telephone voices are harder to >>> understand, I think the problem must be something besides the nominal >>> bandwidth of a telephone. >> The official specification for a voice-grade POTS call is that same >> 300-3000Hz passband. Modern digital systems deliver a 'high end' of >> 4000hz. and often have a lower 'low end' as well. > Some modern phones sound very good. It depends on who's calling.

Some phones are made cheaper than others.

>>>> Does a POTS line from the CO to a house carry multiple voices? >>>> Depending on the location, often times yes. Between central offices >>>> or within the CO almost always yes. I mean if you live across the >>>> street from the CO you probably have dedicated copper pair, but you >>>> live some distance you probably are multiplexed over a carrier line. >>>> The degree of multiplex determines your bandwidth. >>> Would you be able to connect with V90 on a multiplexed line? >> Only in *very* rare situations. >>> As far as capacity goes, I don't know how fast is the digital stream >>> for a voice call, >> After digitalization, a standard POTS voice-grade call uses 64000 > bits/sec. > Is that between telco facilities?

Or even between the telco and _customer_ facilities that use 'digital entrance' to the telco.

>> but I'm sure DSL at 2.5Mb/s requires much more of the telco's >>> capacity. >> "Not Exactly" applies here. The DSL signal rides the wires from the >> customer premises _to_ the telco switching facility. *BUT* before it >> would get to the telco switching gear, it is separated out, >> segeregated, and sent to some *entirely*different* equipment -- called >> a DSLAM, if you care. Frequently that DSLAM equipment does *NOT* >> belong to the telephone company, but to the company providing DSL >> services. the 'upstream' connection out of the DSLAM is a dedicated >> data circuit -- possibly rented from the telco, but often _also_ >> supplied by the company that runs the DSLAM. Regardless, it is not >> using up any capacity on the Telco's VOICE network. > If the telco owns the DSLAM, won't their investment cost depend on > capacity? If they contract for the DSLAM service, won't they be > charged according to traffic?

If the telco itself is offering/providing DSL service, then it is virtually certain that they own the DSLAM equipment. If a third-party provider is doing the DSL provisioning, then the incumbent telco may, or _may_not_ have any involvement with the DSL equipment.

As to 'how things are priced/charged-for', that's a whole 'nuther kettle of fish. Some arrangements are 'flat rate', where you pay a fixed price for the capacity that is available to you. Pthers are so-called 'burstable' rates, where you pay based on how much traffic you send.

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Robert Bonomi
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