Robert Bonomi wrote:
> In article <telecom24.288.13@telecom-digest.org>, Choreboy
> <choreboyREMOVE@localnet.com> wrote:
>> 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.
> 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).
>>>> 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.
>>>> 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?
>> 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.
Choreboy (choreboyREMOVE@localnet.com)