Standards determine whether a given modem can successfully connect with any
other modem in the world.



Bell 103   Uses a kind of modulation called Frequency Shift Keying, or KSK, in
	  which a specific tone frequency signifies a digital one and another a
	  digital zero. Each change in the modem's signal thus carries one bit
	  of digital information. Consequently, the Bell 103 standard is the
	  only one in which the baud rate (the rate at which signals change) is
	  equal to the data rate of 300 bps (Bits Per Second).


Bell 212A  is the next logical step and the second modem standard to find wide
	  application in the United States. It achieves a data-transfer rate of
	  1,200 bps by using phase modulation of a carrier signal. The phase of
	  a fixed tone, called a carrier wave, is shifted by any of four phase
	  angles. Under Bell 212A, the carrier wave can change phase up to 600
	  times per second, or 600 baud. The four phase states are sufficient
	  to represnet any of four two-bit patterns. Thus each baud can carry
	  two bits of information, raising the actual throughput to twice the
	  baud rate of 1,200 bps.

	   While widely used in America, many foreign countries prohibit the
	  use of Bell 212A, prefering instead the similar international
	  standard, V.22.

NOTE: Why do rockwell controllers, in Bell 212A mode require a CCITT V.22 BIS 
answer tone?

Cause their controller code is buggy! However, they've shipped a few million of 
them, so it's a "standard" now.

LAP-B	   stands for Link Access Procedure, Balanced, an error-correction
	  protocol designed for X.25 packet-switched services like Telebit and
	  Tumnet. Some modem makers adapted it to their dial-up products before
	  the V.42 standard was agreed upon. For example, the Hayes Smartmodem
	  9,600, form Hayes Mirocomputer Products, includes LAP-B error-control
	  capabilities.

LAP-M	   is an acronym for Link Access Procedure for Modems and is the
	  error-correction protocol used by the CCITT V.42 standard.

MNP	   Microcom Networking Protocol is an entire hierarchy of standards,
	  starting with MNP Class 1, a no longer used error correction
	  protocol, and running to MNP Class 10, designed to induce the highest
	  data transfer performance from poor connections, especially those
	  found in cellular phone systems.

	   MNP classes 2 though 4 deal with error control and are in the public
	  domain; classes 5 though 10 are licensed by Microcomm

MNP-2	   is designed to work with any modem capable of full-duplex
	  communications. It works by confirming each byte as it is sent - by
	  having the receiving modem echo back each character.

MNP-3	   improves on MNP-2 by wirking synchronously instead of asyncronously.
	  As a result, no start and stop bits are required for each byte,
	  trimming the data-transfer overhead by 25 percent or more.

MNP-4	   is an error correcting protocal that also yields some data
	  compression. It incorporates two innovations. The first, Adaptive
	  Packet Assembly, allows the modem to package data in blocks or
	  packets sent and error-checked as a unit, The second, Data Phase
	  Optimization, eliminates repetitive control bits from the data
	  traveling across the connection to streamline trasnmissions. Together
	  these techniques can increase the throughput of a modem by 120
	  percent at a given bit rate.

MNP-5	   is purely a data compression protocol that squeezes some types of
	  data into a form that transmits faster. MNP-5 can compress up to a
	  factor of two, effectively doubling the speed of data transmissions.
	  On files that have been already compressed, however, MNP-5 may
	  actually increase the transmission time.

MNP-6	   is designed to help modems get the most out of telephone
	  connections, independent of data compression. Using a technique
	  called Universal Link Negotiation, modems can start communicating at
	  a low speed, then, after evaluating the capabilities of the teliphone
	  line and each modem, switch to a higher speed.

MNP-7	   is a more efficient data compression algorithm (Huffman encodeing)
	  than MNP-5, premitting increases in data throughput as much as
	  threefold on some data.

MNP-8	   was never released.

MNP-9	   is desinged to reduce the transmission overhead required by some
	  common modem operations. The acknowledgments of data packets is
	  streamlined by combining each acknowledgement with the next data
	  packet instead of sending a separate confirmation byte. While some
	  error-correction schemes require all information transmitted after an
	  error to be resent, an MNP-9 modem only requires the incorrect data
	  to be sent again.

MNP-10	   is a set of Adverse Channel Enhancements that help medems work
	  better with poor connections, compensating for line noise, echo
	  problems, and limited bandwidth. Modems with MNP-10 will make
	  multiple attempts to set up a transmission link, optimize the size of
	  data packets for a connections, and adjust to the highest rate
	  possible.

V.22	   is the CCITT equivalent of the Bell 212A standard, a transfer rate
	  of 1,200 bps at 600 baud. It uses the same form of modulation as Bell
	  212A but is not compatible with the bell standard, because it uses a
	  different protocol to set up the connection. Some modems support both
	  standards and allow you to switch between them.

V.22bis    was the first true world standard, adopted in both the United States
	  and Europe. It allows a transfer rate of 2,400 bps at 600 baud by
	  using a technique called trellis modulation that mixes two simple
	  kinds of modulation; quadrature and amplitude. Each baud has 16
	  states, enough to code any pattern of four bits. Each state is
	  distinguished both ny its phase relationship to the unaltered carrier
	  and its amplitude (or strength) in relation to the carrier. There are
	  four distinct phases and four distinct amplitudes under V.22bis

V.32	   is an international high speed standard that permits data-transfer
	  rates of 4,800 and 9,600 bps. At 4,800 bps, it uses quadrature
	  amplitude modulation simiar to Bell 212A, but at 2,400 baud rather
	  than 212A's 600 baud. At 9,600 bps, it uses trellis modulation
	  similar to V.22 bis's 600 baud) and with a greater range of phases
	  and amplitudes.

	   Note that while most Group III FAX machines and modems operate at
	  9,600 bps, a FAX modem with 9,600 bps capability isn't necessarily
	  compatible with the V.32 standard.

V.32bis    extends the V.32 standard to 14,400 bps, while allowing intermediary
	  speeds of 7,200 and 12,000 bps in addition to the 4,800 and 9,600 bps
	  speeds of V.32.

	   Note that all of these speeds are multiples of a basic 2,400 baud
	  rate. The additional operating speeds available to V.32bis are
	  generated using different ranges of phases and amplitudes in the
	  modulation. At 14,400 bps, there are 128 potentially different
	  phase/amplitude states for each baud under V.32bis, enough to encode
	  seven data bits in each baud. Because there are so many phases and
	  amplitude differences squeezed together, a small change in the
	  characteristics of a telephone line might mimic such a change and
	  cause transmission errors. Consequently, error detection and
	  correction become increasingly important as transmission speed goes
	  up.

V.42	   is a world wide error correction standard designed to help make
	  V.32, V.32bis and other modem communications more reliable. V.42
	  incorporates MNP-4 as an "alternative" protocol. That is, V.42 modems
	  can communicate with MNP-4 modems, though a connection between the
	  two won't use the more sophisicated V.42 error correction protocol.
	  At the beginning of each call, as the connection is being negotiated
	  between modems, a V.42 modem will determine whether MNBP-4 or full
	  V.42 error correction can be used by the other modem, MNP-4 being the
	  second choice.

V.42bis    is a data compression protocol endorsed by the CCITT. Different from
	  and incompatible with MNP-5 and MNP-7, V.42bis is more efficient than
	  either. On some forms of data, it can yeild compression factors up to
	  four, potentially quadrupling the speed of modem transmissions. (With
	  PCs, the effective saximum communication rate is limited by the
	  serial port itself to no more that 38,400 bps.) Unlike MNP-5, V.42
	  never slows transmission of "incompressible" data. Worst case
	  operation is the same speed as would be achieved without compression.

See also:

• ftp://ftp.kiarchive.ru/pub/.1/misc/standards/itu/ for v. standards

  .