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From: Gord Hannah
To: All
Date: 2011-01-01 01:00:04
Subject: [4 of 12] Comm Primer

    ATX - enable result code formats and tone detection such as busy and
          dial tone
          X0 - most basic, just indicate CONNECT
          X1 - full message indicating line speed, eg. CONNECT 9600

    ATZ - reset modem to startup condition
          Z or Z0 - restore to conditions set in &W0
          Z1 - restore to conditions set in &W1

   AT&C - DCD/RLSD mode
          &C or &C0 - DCD always indicated on to terminal
          &C1 - DCD follows modem carrier

    AT&D - function of DTR line
           see your modem manual

    AT&F - set up factory configuration
           see your modem manual

    AT&W - store present configuration in modem's non-volatile memory.
           see your modem manual and the ATZ command above.

    These represent only a fraction of the commands available in any
    one modem, but beyond this, implementations of the AT command set
    begin to diverge widely and wildly.


    When implementors of modems are too lazy to conjure up a new AT
    command for a new function, the function is instead left in something
    called an S-register.  These vary even more widely between
    manufacturers than do the AT commands, so you are best off to remain
    away from these if and when you possible can.  Good manufacturers
    will have most or all of the functions in any S-register replicated
    in an AT command, with the exception of the first 13 "classical"

    S0 = number of rings before modem is permitted to grab the line
         (0 = no answer, ie. AutoAnswer off)
    S1 = ring count - read only, cannot be set
    S2 = escape code character - normally set as "+" to use +++
    S3 = carriage return, or RETURN or ENTER, character
    S4 = line feed character
    S5 = backspace character
    S6 = wait after going off hook, before dialling
    S7 = length of maximum wait for carrier after dial
    S8 = pause for "," in dial string - see details in your modem's
         ATD command
    S9 = carrier detect response time
    S10 = lost carrier to hangup delay
    S11 = tone duration during tone dialling
    S12 = escape code guard time

HSP - (H)ost (S)ignal (P)rocessor - a modem that depends of the CPU of
the host system for part or most of the data/signal processing.

HST - (H)igh (S)peed (T)echnolgy - a family of proprietary high-speed
modulation and error-correction protocols developed by US Robotics.

IRQ - (I)nterrupt (R)e(Q)uest Line - a hard-wired path to a CPU which
requests on a prioritized basis that the processor interrupt a task in
progress. On DOS systems, Comm Ports 2 and 4 are assigned to IRQ3, and Comm
Ports 1 and 3 are assigned to IRQ4. By virtue of Comm2 and 4 having a lower
(thus higher priority) IRQ, it is preferable to have a high-speed device
such a a modem attached to it when running multi-tasking platforms which
run on top of DOS, or when using multiple serial devices (eg. mouse and

ISDN - [I]ntegrated [S]ervices [D]igital [N]etwork is a set of standards
for transmission of simultaneous voice, data and video information over
fewer channels than would otherwise be needed, through the use of
out-of-band signalling. The most common ISDN system provides one data and
two voice circuits over a traditional copper wire pair, but can represent
as many as 30 channels. Broadband ISDN extends the ISDN capabilities to
services in the Gigabit range.

  BRI- A Basic Rate Interface is two 64K bearer ("B") channels and a
  single delta ("D") channel.  The B channels are used for voice or
  data, and the D channel is used for signaling and/or X.25 packet
  networking.  This is the variety most likely to be found in
  residential service.

  PRI - Primary Rate Interface. Inside North America and Japan, this
  consists of 24 channels, usually divided into 23 B channels and 1 D
  channel, and runs over the same physical interface as T1. Outside of
  these areas the PRI has 31 user channels, usually divided into 30 B
  channels and 1 D channel and is based on the E1 interface.  It is
  typically used for connections such as one between a PBX (private
  branch exchange, a telephone exchange operated by the customer of a
  telephone company) and a CO (central office, of the telephone company)
  or IXC (inter exchange carrier, a long distance telephone company).

ISP - (I)nternet (S)ervice (P)rovider, an organization that provides
access to the internet.

ITU-T - Formally the International Telecommunications Union - Technical
Standardization Sector. it is a consulting arm of the United Nations
chartered with the setting of international standards for
telecommunications services and equipment. Its members are the national
authorities in each country responsible for regulating and providing
telecommunication services. It should be noted that though the ITU is
chartered with technical tasks, it is a political organization, and
therefore subject to all of the trappings thereof.

KERMIT - Kermit is a protocol designed for transferring files between
micro- computers and mainframe computers.  It was developed by Frank DaCruz
and Bill Catchings at Columbia University in New York and is widely
accepted, especially in the academic world.  Kermit was named after the
fuzzy, green talking frog of Jim Henson's "The Muppet Show".

There are both public domain, and copyrighted Kermit programs that not only
include the protocol but are complete programs in themselves offering the
communication functions needed for the particular machine on which they are

LAP-M - (L)ink (A)ccess (P)rocedure for (M)odems - an error control
protocol incorporated into ITU-T recommendation V.42.

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