Communication Standards

Author: Bill Karwin
Copyright: (c) 1994 Bill Karwin
Version: 0.5 July 8th, 1994
[This is a preliminary copy.]
Updated by Wolfgang Henke, 03/11/1996

We need standards so we can talk to each other.

ITU-T     The International Telecommunications Union Telecommunication
          Standardization Sector (formerly called the CCITT) makes
          recommendations for global telecommunications standards.
          They're the people who design and approve most of the "V.xx"
          standards you hear about all the time.

bis/ter   Sometimes ITU standard names have a suffix, either "bis" or
          "ter".  These mean "two" and "three", respectively.
          So V.32bis is like saying, "V.32 -- The Sequel!"
	  "terbo" seems to be a play on words.

baud vs. bits per second
          The highest number of individual signals per second on a
          phone line is 2400.  If you only have two different tones
          then you are transmitting 1 bit per signal, or 2400bps.
          Higher modem bits-per-second rates are achieved by transmitting
	  more bits per signal, using more than two distinct tones.


Bell 103  300bps USA standard.
V.21      300bps.
Bell 212A 1200bps USA standard. (same as V.22? *)
V.22      1200bps with fall back to 600bps
V.23      1200bps with 75bps back channel, fall back to 600bps/75bps
          Used by Brazilian Videotext service.
V.22bis   2400bps with fall back to V.22
V.32      9600bps with fall back to 4800bps
V.32bis   14400bps with fall back to 12000bps, 9600bps, 7200bps and 4800bps
V.32terbo 19200bps, with fall back to 16800bps and V.32bis
V.34      28800bps.  Approved 6/9/94.  Previously called V.FAST.  Includes:
          o "line probing", to test reliability of a connection.
          o 28800bps half-duplex transmission for FAXes.
          o fallback to existing V-series modems.
          o 200bps channel for modem control data.
          o Trellis coding to correct for line noise.
          o Handshaking with telephone network equipment. *
V.FC      "V.Fast Class" 28800bps industry standard, by Rockwell and Hayes.
          Not an ITU-T recommendation, despite the "V." prefix.
          Incompatible with V.34, but many modem vendors may offer 
          dual-standard modems.


V.27ter   4800bps with fall back to 2400bps
V.29      9600bps with fall back to 7200bps and 4800bps
V.17      14400bps with fall back to 12000bps, 9600bps and 7200bps
V.34      28800bps.


HST       9600bps/14.4kbps/16.8kbps/21kbps/24kbps "High Speed Technology",
          US Robotics' proprietary full duplex protocol.  USR puts out modems
          that use HST, modems that use V.32bis, and modems that support both
          standards, called "dual-standard".

PEP       "Packetized Ensemble Protocol", Telebit's proprietary 9600bps
          full duplex error-correcting protocol.  Reported to sustain noisy
          connections better than V.32.  TurboPEP is an improvement, and can
          achieve 24000bps or more.

Express 96 "Ping Pong Protocol", Hayes' proprietary 9600bps protocol.

CSP       "CompuCom Speed Protocol", CompuCom's proprietary 9600bps protocol.
          In 1992, the SpeedModem Champ was unique in that it was cheaper than
          V.32, but CompuCom went out of business.


V.42      Error correction with asynchronous to synchronous conversion.
          Includes MNP-1 through MNP-4 and LAP M.  Not used by UUCP, kermit,
          xmodem, etc., since they do their own error correction.

V.42bis   Data compression.  The rhetoric claims you can get compression
          up to 4:1, but it is more typical to get 2:1 or maybe 5:2.
          V.42bis always uses V.42 error correction.

MNP       "Microcom Network Protocols"
MNP1      Asynchronous, half duplex transfer.
MNP2      Simple error correction, asynchronous, full duplex.
MNP3      Error correction, synchronous.  Not a big win over MNP2.
MNP4      Error correction, better throughput than MNP2-3.
MNP5      Simple data compression, about 2:1.  Often included with V.42.
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.

LAPM      "Link Access Protocol for Modems".  AT&T/Hayes error correction
          standard.  Included in V.42.


CAS       IBM and DCA standard for computer-faxmodem interface.
Class 1   Electronic Industries Association/Telecommunications Industry
          Association standard for minimal computer-faxmodem interface.
Class 2   EIA/TIA standard for extended computer-faxmodem interface.
Group 3   Fax protocol.  9600bps.  203x98dpi/203x196dpi.  Compression.
Group 4   Fax protocol.

V.24      Connection between DCE and DTE.  Effectively the same as RS232,
          though V.24 only specifies the meaning of the signals, not the
          connector nor the voltages used.
V.25bis   A cryptic command language for modems.
V.54      Modem diagnostics standard, frequently included by V.32 modems.
V.18      Interoperability for communications devices for the deaf.


Name            Bandwidth  Notes
DS-0              64 kbps  Equal to one voice phone connection.
DS-1           1.544 Mbps  Used for T1.  Secondary Internet connections.
DS-1C          3.15  Mbps  Not used.
DS-2           6.312 Mbps  Only used for microwave.
DS-3          44.736 Mbps  Used for T3.  Primary Internet backbone.
OC-1          51.840 Mbps  SONET level 1.
OC-3         155.530 Mbps  SONET level 3. NFS's vBNS 
DS-4         274.100 Mbps  Not used.
M560         560.000 Mbps  Proprietary.  Current telephone backbone.
OC-24      1,244.16  Mbps  Also called G1.
OC-48      2,488.32  Mbps  Also G2, Future telephone backbone.
OC-192     9,953.28  Mbps  Also G8, Not available yet.

ISDN is a normal phone line, used for digital data instead of an
  analog signal.  The wires carry two "B channels", each capable of
  64kbps.  There is also a 16kbps "D channel" normally used only for

Leased Lines are DS-0 lines, with some bits stolen for signalling,
  so the line ends up being 56 kbps.

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Bill Karwin                        

WH Networks

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