>>. I know there are a couple different kinds of speed data being mentioned here lately which I haven't yet sorted out...
Yes, there were other posts which I hadn't read that explained
it better than I did.
DCE vs DCT speeds are merely the speed the modem communicates
with the computer vs the speed it communicates with the
communication line. With compression, the two don't have to
be equal, so you can get (say) 56kb off the line, decompress it,
and ship 115kb to the computer, and vice-versa. When the
modem is compressing/decompressing data, bit rate in one side
doesn't have to equal bit rate out the other.
Simple, no?
The point about the upper limit on the DCE speed is that
the UART in the serial port has to be able to handle the
max uncompressed bit rate (the high one). Up till two
or three years ago, you had to go pay for a port that could
handle 115kb. Now, they all come with it. You get to
go pay for a port that will handle higher. I forget the
new top end, and also the numbers of the UARTS. Used to
know 'em by heart when I was shipping mostly text <gg>.
BTW, UART is universal asynchronous receive/transmit.
Async serial I/O in other words, though v.3xx/4xx up actually
goes synchronous at the higher bit rates, I believe.
(Translation: async means, roughly, that one "character"
can follow another at an indefinite later time; synchronous
means it follows at a specific interval. This is oversimplified,
but the right idea. Synchronous is faster at the same
bps because you can omit synching bits [called start/stop bits]
because the receiver knows when the next bit is supposed to
arrive.) |
