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From: Gord Hannah
To: All
Date: 2011-02-15 01:00:00
Subject: [6 of 12] Comm Primer

    programmable (Flash) type ROM memory (eg. USR Courier). In other designs
    DSP code is stored in driver files on the user's system (eg. USR
    WinModem, IBM MWave).

       CAVEATS: In general, operational characteristics relative to basic
       modulation functions are unalterable when "static" ROM is employed
       (ie. bug fixes, changes in protocol implementation, or support for
       new operational modes, cannot be accomplished without physically
       changing the data pump).

       The USR WinModem is a special case of the configuration where DSP
       code is loaded in the form a a driver from the user's system in that
       it is platform specific - it will only function under Windows
       incarnations where virtual device drivers are supported (ie. Windows
       3.X and Windows 95), IT CANNOT BE USED UNDER DOS, OS/2, WINDOWS NT,
       OR ANY FLAVOR OF *NIX.

    The controller section is typically composed of a general purpose CPU
    and ROM where code governing the command interface, higher-level
    protocols (eg. error correction and data compression), facsimile
    functions, and ring pattern recognition, etc, are implemented. As is the
    case with the DSP section, the type of ROM used varies. The typical
    design employs fixed ROM, but many vendors have begun to use flash
    memory in the high-end models. The controller section of the modem is
    typically what is referred to when a particular model advertises that it
    employs Flash ROM.

MNP - (M)icrocom (N)etworking (P)rotocol - a family of proprietary error
correction and data compression protocols developed by Microcom. MNP levels
1-4 are error correction protocols, and MNP level 5 is a complementary data
compression protocol which functions under MNP4 error control. NOTE: MNP
Levels 1-4 have been placed in the public domain by Microcom.

   MNP1     Asynchronous, half duplex transfer.
   MNP2     Error correction, asynchronous, full duplex.
   MNP3     Error correction, synchronous.  Not a big win over MNP2 about
            20%.
   MNP4     Error correction, better throughput than MNP2-3. a modification
            which rides on top of MNP2 or 3 to improve throughput.
   MNP5     Simple data compression, about 2:1.
   MNP6     Statistical duplexing and Universal Link Negotiation.
            With V.29, modems can emulate full duplex operation.
            Also supports fall-forward operation between two MNP modems.
   MNP7     Data compression, about 3:1.
   MNP8     MNP7 for pseudo-duplex modems.
   MNP9     Data compression, about 3:1.  Includes V.32 technology. (?)
   MNP10    Dynamic fall-back and fall-forward adjusts modulation speed
            with link quality. Intended for use for cellular, but doesn't
            work too well for cellular transmissions!

NYQUIST THEOREM - a fundamental dictum of data communications that governs
channel capacity. In simple terms it states that frequencies can only be
accurately reproduced at up to half the sampling rate. Stated differently,
the maximum theoretical signaling speed of a channel in baud is twice its
bandwidth.

Relative to the telephone system, it dictates that no frequency above 4kHz
can be transmitted over a typical phone line.

OCTET - An octet is a string of 8 bits, and not necessarily the same thing
as a byte. Communications switches transfer information by the octet. If you
are using a packet switch to transfer telex messages, then every 8
characters will occupy 5 octets. If you are transferring a binary file from
one PC to another, then every 8 characters will occupy 8 octets.

PCM - (P)ulse (C)oded (M)odulation, a method of encoding an audio signal
in digital format.

PEP - (P)acketized (E)nsemble (P)rotocol - a proprietary multi-carrier
high-speed modulation protocol developed by Telebit.

POP - (P)oint (O)f (P)rescence, a dial-in point for acessing an ISP.

POTS - (P)lain (O)ld (T)elephone (S)ervice - an ordinary voice quality
telephone line.

PROTOCOL - A protocol is a set of rules governing the communication and the
transfer of data between two or more devices.  The rules define the
handling of certain communication problems, such as framing, error control,
sequence control, transparency, line control, and start-up control.

The Technical Standardization Sector of the International
Telecommunications Union, (ITU-T) renders technical recommendations which
are typically adopted as standards by manufacturers of telecommunications
devices. The recommendations are referenced with an alphanumeric
designation of the form V.### which may also include a modifying suffix
such as "bis" or "ter" (meaning second and third
respectively). The
suffixes signify a complementary modification or extension of an existing
like-numbered recommendation (eg. V.32 relates to modulation technology for
operation of modems on the GSTN at 9600 and 4800bps DCE rates, while
V.32bis modifies and extends the scope of V.32 to include rates of 4800,
7200, 9600, 12000, and 14400bps, plus add logic for enhanced retrain
turnaround). Similarly, but somewhat different, V.42 recommends
error-control methodology, and V.42bis defines data compression technology
which functions under V.42 error-control.

In addition to the standards established by ITU-T recommendations,
manufacturers offer products which feature proprietary modulation or error
control technology which may be technically and/or functionally superior to
the methods recommended by ITU-T.

RBOC - (R)egional (B)ell (O)perating (C)ompany, one of the "Baby Bell"
teleco operating companies created by the government mandated break-up

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