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Bell 103J U.S. standard 300bps
Bell 212A U.S. standard 1200bps
CCITT V.17 Int. fax standard 14400bps
CCITT V.21 Int. standard 300bps
CCITT V.22 Int. standard 1200bps
CCITT V.22bis Int. standard 2400bps
CCITT V.23 Int. standard 1200 and 75bps
CCITT V.24 Serial interface standard (EIA/RS232-D)
CCITT V.27ter Int. fax standard 4800bps
CCITT V.29 Int. fax standard 9600bps
CCITT V.32 Int. standard 9600 and 4800bps
CCITT V.32bis Int. standard 14400/12000/9600/7200/4800bps
CCITT V.34 Int. standard 28800/26400/24000/21600/19200 .. to 2400bps
CCITT V.34+ Int. standard same as V.34 plus X2 technology up to 56000bps
CCITT V.42 Standard for detection and negotiation for LAPM
CCITT V.42bis Extension of V.42 specifying the data compression protocol
CCITT V.FAST Int. standard 28800bps
ITU V.90 Int. standard 56000 kBit/s
X2 and K56Flex Modem's are not compatible to V.90.
Most of this Modems (X2 and K56Flex) can be upgraded for V.90 (Flash-code).
V.110 ISDN Europe (old) 38400 kBit/s
V.120 NDIS U.S. 57600 kBit/s
X.75 ISDN Europe std. 64000 kBit/s
T70 BTX <-> ISDN Europe 64000 kBit/s
ISDN - Integrated Services Digital Network (Germany - Europe)
NDIS - Network Device driver Interface Specification (USA)
DSS1 - Digital Subscriber Signalling System No. 1 (aka Euro ISDN)
1TR6 - ISDN-Protocol for D-channel / control for (up to 30) B-channels - Germany only
(1TR6 is now obsolete -> use DSS1)
Error Control
There are two important sets of standards that define how transmission errors are to be detected and
corrected. They are MNP (Microcom Networking Protocol) classes 2,3 and 4 and the CCITT V.42.
V.42 uses a protocol called LAP-M (Link Access Protocol for Modems). For compatibility, V.42 contains MNP 2-4.
Data Compression
To reduce the amount of data that must be transmitted, there are two important standards
that describe automatic data compression. They are MNP class 5 and CCITT V.42bis.
V.42bis requires that both modems use V.42 error control with LAP-M. It is claimed that MNP 5
offers 2:1 compression and V.42bis offers 4:1 compression. If this were true, we would see
the following effective speeds:
2400bps + MNP 5 --> 4800bps
2400bps + V.42bis --> 9600bps
9600bps + MNP 5 --> 19200bps
9600bps + V.42bis --> 38000bps
14400bps + MNP 5 --> 28800bps
14400bps + V.42bis --> 57600bps
The actual throughput is significantly less and depends on the type of data being transmitted.
(Because MNP/V.42 uses near the same algorithmus than compression programs, a packed file transmitted
with MNP will have the same throughput, as a transmit w/o MNP, but when you send uncompressed ASCII-text or binary
files then the transmission speed will be faster than w/o MNP or V.42)
AT Command's (ATtention cmd.)
The AT command-set is not standarized , always use the literature and software that comes with the
modem. However, this description should assist, to understand the basic's of TELE-PROCESSING.
Under no circumstances try to work / manipulate a MODEM during a THUNDER-STORM !
MODEM's are normally shipped, with a tailored software-package. During start testing a MODEM, always use
the software that comes with the MODEM. The defaults included in such a modem program (protocol used for DIAL / RESET / COMMUNICATE) will
work in near all situations.
When you enter AT command's, the input should be done, either in UPPER or LOWER case (do not mix).
MODEM Data Terminal Interface
The modem connector interfaces with the DTE via a 25-pin connector.
(for 9-pin DB-9 connector see > Serial DB-9 pin-layout).
| Pin | EIA-232C Circuit |
CCITT V.24 Circuit |
Function |
|---|---|---|---|
| 1 | AA | 101 | Frame ground (FG) |
| 2 | BA | 103 | Transmitted data (TD) |
| 3 | BB | 104 | Received data (RD) |
| 4 | CA | 105 | Request to send (RTS) |
| 5 | CB | 106 | Clear to send (CTS) |
| 6 | CC | 107 | Data set ready (DSR) |
| 7 | AB | 102 | Signal ground (SG) |
| 8 | CF | 109 | Data carrier detect (CD) |
| 9 | +12 V dc voltage reference | ||
| 10 | -12 V dc voltage reference | ||
| 11 | Flow control | ||
| 12 | CI | Speed indicator (from DCE) | |
| 15 | DB | 114 | Transmitter signal element timing (from DCE) (TC) |
| 17 | DD | 115 | Receiver signal element timing (from DCE) (RC) |
| 20 | CD | 108/2 | Data terminal ready (DTR) |
| 21 | 140 | Remote loopback command | |
| 22 | CE | 125 | Ring indicator (RI) |
| 23 | CH | External speed control (from DTE) | |
| 24 | DA | 113 | External transmit clock (ETC) |
| 25 | CN | 141 | Analog loopback command |
Please see the LEGAL - Trademark notice.
Feel free - send a 
for any BUG on this page found - Thank you.