Reed
Guest
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 Posted:
Sun Oct 30, 2005 12:53 am Post subject:
Re: Unattended Initiate (UI) and Round Robin (RR) |
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Perdition wrote:
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I need to learn about these two modem features/mechanisms but I can't
find anything in my available literature or by googling. I'm hoping
someone can explain these to me or give me a good site/ebook on both,
also if anyone knows where I can learn about Constant and Switched
Carriers I would be grateful :) Thanks alot in advance
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The terms UI and RR, while probably not exclusive to them, were
used by 9600bps 4-wire analog modems of the 1970's made by Codex
Corp of Newton, MA, USA. (later a sub of Motorola, since sold
off).
Analog modems that use complex modulation schemes like QAM need to
be in constant synchronization. Prior to the advent of UI,
re-synchs (retraining) would be done manually as needed. UI meant
the modem itself could detect loss of sync and start the retrain
process automatically.
RR is an extension of this, merely meaning the retrain would be
accomplished in both directions on the 4-wire circuit. Prior
methods might only retrain in one direction.
Constant Carrier means that the modems analog carrier signal is
constantly sent into the circuit, usually on a point-to-point
circuit
Switched Carrier means the modem's (DCE) signal is turned on and
off as data is ready to be sent by the terminal device (DTE). This
switching is controlled by the DTE, using the RTS (Request To
Send) lead in the DCE/DTE interface. Switched carrier is used in
applications where Constant carrier is not possible. Some of these
are:
Multidrop circuits
2-wire circuits & Modulation schemes that do not allow CC; ie Bell
202 & 208
Since this all predates the Internet by about 20 years, you may
only be able to find written info in old user manuals of the era,
or older technical references at a library.
Good luck,
Reed |
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