[Tutor] OT: need computer advice from wise Tutors

[David Hutto]

On Wed, Jun 30, 2010 at 3:06 AM, ALAN GAULD <alan.gauld at btinternet.com> wrote:
>
>
>> > If its a typical ADSL line it will be conneced to a DSLAM at
>> > the centeral office(by the telco) and  that will be shareed.
>>
>> > ADSL also loses bandwidth the further you are from the office
>
>> process has to be diversified for each customer, because it
>> all travels at the speed of light.
>
> It is diversified on the individual line leading to your house
> but it is shared from wherever it gets converted to a digital
> multiplex. That could be at the roadside cabinet or at the
> central office. At that point the data is mixed together
> using a round-robin type algorithm. The more active signals
> that are present the lower the proportion of the total bandwidth
> available to each.
>
> The speed of transmission is not really relevant (it only affects
> transit time not bandwidth) although it is as you say the
> speed of light (but not the speed of light in a vacuum, much
> lower than that) within the bearer. However within the electronics
> the signal travels more slowly - around the speed of sound - but
> fortunately for very small distances.
>
>> sometimes had a weak signal depending on the distance
>> from the consumer. This signal could be modified from the cable
>> company, so the box amplified the 'weak', but not further away,
>> signal.
>
> Its not a matter of signal strength but of signal smearing as it
> travels along the line. The digital data is sent as pulses (a great
> simplification!) but those pulses lose their shape as they travel
> along the line until eventually the electronics cannot distinguish
> one from another. The only way to improve is to send the
> pulses more widely spaced, which reduces the bandwidth,
> or to have repeater boxes which regenerate the pulses at
> regular intervals. On long distance routes, between cities, the
> telco will install repeaters but for domestic use they progressively
> reduce the bandwidth.
>
>> So this would also be a matter of what was being sent/received
>> being modified, depending on the priority (given by the ISP provider)
>> of the current DSL (or whatever connection) consumer?
>
> No, it doesn't matter what priority the comnsumer has it is down
> to the physical characteristics of the line. Telcos typically use
> copper or aluminium conductors in the local lines with paper
> or PTFE insulation and either crimped, twisted or soldered joints.
> All of these affect the transmission characteristics but the biggest
> factor is the length of the line. Its not economical to install
> repeaters in every consumer line so the bandwidth must be
> adjusted to match what the line is capable of. (This is done
> dynamically so you may even find your bandwidth varies slightly
> depending on the weather!) In practice it should be fairly stable
> and the biggest variations will be due to contention at the
> DSLAM.
>
> HTH,
>
> Alan G.
> (Who works for a telco! :-)
>
>

Thanks for taking the time to answer, and sorry for somewhat hijacking
the op's thread.