I don't have a link, but I can provide some advice. To understand these
words, remember your linguistics or Greek classes from college. You did
take such classes, I hope!? ;-) Math classes help also. What is an
isosceles triangle, for example? A triangle with two equal sides. Iso means
"equal" in Greek.
According to Webster's, isochronous or isochronal means uniform in time,
having equal duration, recurring at regular intervals. For example, a
multimedia application might require a transport that delivers data at
regularly occurring, equal intervals. The intervals between data delivery
events are all equal so that voice and video are not jerky.
Asynchronous means no timing. Adding an "a" negates something in Greek,
such as an amoral person who has no morals. Data can be delivered at any
time with asynchronous transmission.
Synchronous is similar to isochronous, but has the additional restriction
that data is delivered at specific intervals. A common timing is
established between communicating stations so that both sides know when it
is OK to send data. There is a separate clocking signal used to get both
sides "in synch." SONET is an example of a synchronous system. Manchester
encoding and other LAN encodings are isochronous. With LAN technologies,
clocking, which is embedded in the signal with the data, occurs at regular
intervals, but the communicating stations do not synch up to a clock first.
For communications to be truly synchronous, they must share a clock. You
are probably aware of WAN technologies that require a network clock.
Plesio means "almost" in Greek. Plesiochronous systems, such as the North
American Digital Hierarchy and European E systems, are almost synchronous.
They have almost all the same characteristics of a truly synchronous
system: a clocking signal, data sent at specific intervals, etc. But the
communicating stations are not sourced from the same clock and so, over the
long term, get skewed from each other. The inaccuracy of timing will force
a WAN switch, over time, to repeat or delete frames in order to handle
buffer underflow or overflow. These are called frame slips.
I have also read that one of the problems with plesiochonuos systems is
that it is hard to break out one channel. Although isolating a 64-Kbps
channel from a DS-1 circuit is straightforward, isolating a 64-Kbps channel
from a DS-3 trunk requires demultiplexing to the DS-1 level first. SONET
does not have this problem.
Hope that didn't muddy the waters too much!? ;-)
Priscilla
At 11:26 AM 7/16/01, Donald B Johnson jr wrote:
>Does anyone have a link to some detailed information concerning isochronous,
>pleisochronous, or any other flavor of communication. I did a couple of
>searches and was not satisfied with the results.
>Thanks
>Don
________________________
Priscilla Oppenheimer
http://www.priscilla.com
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=12519&t=12486
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