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.
DUPLEX MODEM TRANSMISSION STANDARDS:
Bell 103 300bps USA standard.
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
HALF-DUPLEX MODEM TRANSMISION STANDARDS (USED FOR FAX):
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
PROPRIETARY TRANSMISSION PROTOCOLS:
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.
ERROR CORRECTION & DATA COMPRESSION STANDARDS:
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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Warum ist die Banane krumm?