> > POTS is about analouge transmition, but the media isn't as clear as
> > you might think. Depending on the kind of connection, and the used the
> > bandwidth may reach up beyond 30 kHz, alowing rates of more than
> > 100 Kbps transmission - remember, POTS starts as direct coupled
> In the US, POTS service is bandlimited to roughly 300-3300 Hz.
AFAIR over here it's 300-3000 Hz (to fit within a 3000 Hz chanel when
multiplexed, together with a 200 Hz signaling chanel)
> The
> local loop (between you and the CO) has more bandwidth, which is why
> it can (sometimes) be used for ISDN or DSL, but the switched voice
> network does not.
I tried to bring in _real_ old switches :)
> I was of the impression that POTS in the rest of the world worked
> similarly, but I could easily be mistaken about that.
If you take POTS just as the minimum standard as suportet
(almost) everywhere, you're right, but thruout the years
there have been several diferent technologies used and it
was (before the network was completly digitalised) possible
to find different situations if you tried things outside
the guaranteed bandwidth. (And sometimes you even had lines
where not even the guaranteed signaling was possible.)
> > But in fact, this is all history, POTS no longer exists over here
> > since years.
> Really? You can't use cheap analog telephones any more? I knew ISDN
> was more widely deployed in some other countries than in the US, but I
> had no idea that it had completely displaced POTS.
Shure, you can still get an analouge line, but this is only analogue
until the next switch - sometimes they even insall an ISDN-NT in your
basement with an integrated a/b adaptor to fullfill the request. The
last (partly) analouge switch has been abdoned here in Germany some two
years ago.
The situation varies within Europe, Germany just jumped first on
the ISDN trail.
> Even so, however, if you use an ISDN B channel for a voice bearer to carry
> alaw or mulaw audio samples, you still can't get more than 8000 baud through
> it in any particularly useful or effective manner.
Speaking of chanels - there is also a neat offering for the D channel:
A permenent X25 connection with no time based payment. Neat if you got low
data rates but round the clock availability (up to 9600 bps).
> The actual baud rate of the raw ISDN BRI varies. In the US it uses 2B1Q
> signalling, with a rate of 80 Kbaud in each direction. Other countries
> use other signalling schemes, such as 4B3T. IIRC, Germany uses a different
> scheme than most of Europe. However, in most countries the telephone
> company provides the ISDN NT1, so the customer equipment is connected to
> the S/T interface, which is the same worldwide.
Within the system even in Germany there are different signalings, but
thats without any influence, thanks to the NT - but even here Germany
had it's own protocoll (1TR6) - thats the curse of beeing early. But
nowadays 1TR6 is only available on special request for compatibility
issues (Sad, since it had some realy neat features).
Gruss
H.
ObCC: Has anyone an issue of Captain Zilog for sale (or is willing
to provide a colour copy) ?
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HRK
Received on Thu Apr 01 1999 - 16:03:56 BST