31 Mar
1999
31 Mar
'99
7:50 a.m.
I have an 7 KBaud modem over here so, where's your
stick ?
(Hint: server side of an 56K analouge dial in :)
(small print: the calculation can be done different :)
As I understand it, a baud is 'number of signal changes per
second'. If you use an encoding method which requires a signal
change for each bit, then 9600baud = 9600bps. Another encoding
scheme might only require 4800baud (4800 signal changes) to get
9600 bps across the wire.
In this case, it sounds like your modem uses a scheme which
somehow gets 4 bits across the wire per signal change, so
7Kbaud (7000 signal changes per second) gets across 56Kbps
(56000 bits per second).
Megan Gentry
Former RT-11 Developer
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31 Mar
31 Mar
9:42 a.m.
Hans wrote:
I have an 7 KBaud modem over here so, where's your
stick ?
(Hint: server side of an 56K analouge dial in :)
(small print: the calculation can be done different :)
Megan wrote:
In this case, it sounds like your modem uses a scheme
which
somehow gets 4 bits across the wire per signal change, so
7Kbaud (7000 signal changes per second) gets across 56Kbps
(56000 bits per second).
No, if it was 7Kbaud and 56Kbps, it would need to get 8 bits per symbol,
not 4. 7000 symbols/second * 8 bits/symbol = 56000 bits/second. Note
that this would require a constellation of 256 distinct symbols (2^8).
However, as previously noted, 56K modems actually operate at 8000 baud,
with up to 7 bits/symbol.
Anyhow, this is OT for another 7 years or so.
10:49 p.m.
[56K/ISDN technology]
However, as previously noted, 56K modems actually operate at 8000 baud,
with up to 7 bits/symbol.
AFAIK the US ISDN uses only 56K chanels - or am I wrong ?
Anyhow, this is OT for another 7 years or so.
Depends on personal experiance - I got my hands on ISDN
equippment first in 1981, and used ISDN Parts for my own
design first in 1985 (to rebuild an /370 Mainframe into
a voice mail system). So, from this point it is clearly
older than 10 years, if you have (had) access to the
early development samples - but Even when thinking of
mass availability, ISDN and ISDN based technologies
already fit into the 10Y rule - at least here in Germany.
Gruss
H.
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Ich denke, also bin ich, also gut
HRK
1 Apr
1 Apr
4:59 a.m.
Hans wrote:
Yes, but the topic was 56K voice-band modems, which have not existed that
long.
Eric
AFAIK the US ISDN uses only 56K chanels - or am I
wrong ?
No, both 56K and 64K ISDN B channels are available in most of the US.
But we were talking about using a 56K voice-band modem (V.90, X2, or K56flex)
on a POTS line. The server end uses ISDN.
The data rate on the POTS line is limited to 53 Kbps by FCC regulations.
The signalling on the POTS line is 8000 baud with up to 7 bits per symbol.
At the server end, the data is still 8000 samples per second, of 7 bits
each. However, those samples are presented digitally, so in some sense it
could be considered to be 56000 baud at the server end *only*. On the other
hand, to be decoded properly, the modulation technique is such that the
integrity of the byte framing of the samples must be maintained, so
effectively it really is still 8000 baud.
Anyhow, this
is OT for another 7 years or so.
Depends on personal experiance - I got my hands on ISDN
equippment first in 1981, and used ISDN Parts for my own
design first in 1985 (to rebuild an /370 Mainframe into
9179
days inactive
9180
days old
3 comments
3 participants
participants (3)
-
eric＠brouhaha.com -
Hans.Franke＠mch20.sbs.de -
mbg＠world.std.com