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From: cyamamot@aludra.usc.edu (Cliff Yamamoto)
Newsgroups: comp.dcom.modems,sci.electronics
Subject: Please define these CCITT
Summary: Just a few lines of explanation each
Keywords: CCITT, modems, protocols, compression, error correction
Message-ID: <12087@chaph.usc.edu>
Date: 21 Sep 90 06:07:38 GMT
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I've been thinking about gettinng a 9.6Kb modem, but w/ all these
standards, I'm confused.  I'm not too interested which is better or
more popular, just what the *heck* is each one?  Can anyone shed
some light on the following:

V.32    - Is this *real* 9600 baud at full duplex?

V.22bis - ????

V.22    - Was this the "fake" 9600 that ran 300 baud in one direction but
          9600 baud in the other, and used some 'ping-pong' algorithm to
          see who sends at 9600 baud?

V.21    - ????

V.13    - ????

V.23    - ????

PEP     - Don't know what each letter means, but this is some proprietary
          Trailblazer error correction and/or compression technique used
          by Telebit?  Does it substitute the V.42 and/or V.42bis?

HST     - Is this another proprietary error correction and/or compression
          technique from US Robotics?

Bell103 - I think this is what defines the 300 baud analog modulation and
          demodulation characteristics.

Bell212 - And this defines the 1200 baud full duplex analog characteristics.

Bell202 - Was this 1200 baud half duplex analog characteristics?

V.42    - Some sort of error control, does it ONLY run with V.32?  Can
          it work without any data compression?

V.42bis - Data compression.  Does it NEED to have V.42 to work properly?
          Does this V.42bis only work at 9600 baud and faster?

MNP2-4  - Error control from Microcom?  Like V.42 but different capabilities.
          Does it ONLY run with V.32?

MNP5    - Data compression from Microcom?  Does this work with MNP2-4?
          Does it only work at 9600 baud and faster?

V.25bis - ????

Yes, these are a lot of questions, but I'm sure there must be someone
out there who'd like to know about this stuff.  I guess I'd like to see
some hierarchy diagram too like:
       
 Serial | Compression |  Error  |  Analog   | Band-limited
  Data  |  Algorithm  | Correct | Mod/Demod |   carrier
------------------------------------------------------------
       +-->   MNP5  ---> MNP2-4 -+
RS232 ----> V.42bis --->  V.42  --> V.32 -----> phone-line
       |                                  |
       +--> V.22bis --->  none  --> V.22 -+

                  (just an example)

Is that diagram even correct?  I am used to the encapsulated format of
TCP/IP and I guess I'm expecting this modem stuff to be the same.  Also
as a side question, do all these "multi-CCITT/MNP" modems use DSP?  Is
it better if the modem has a DSP chip in it?  I understand the data
compression (V.42bis/MNP5) requires a lot of CPU power.  What do the
more powerful modems use? (80188/68000).

Thanks for any and all responses.  If I get enough email, I will compile
all posted replies and email replies into a summarized post.

Regards,
Cliff Yamamoto