Terms To know
- ARQ - Automatic Repeat Request. A general term for error control protocols featuring
hardware detection and retransmission of defective data. This term is used primarily by US
- ASCII - American Standard Code for Information Exchange. A 7-bit binary code
representation of letters, numbers and special characters. It is universally supported in
computer data transfer.
- Asynchronous - Data transmission in which the actual data is preceded by a start bit and
followed by a stop bit since the time between transmitted characters varies. Compare
- Auto Answer - The modem feature which enables detection of a ring and answering without
assistance from a program.
- Baud Rate - The number of discrete signal events per second occurring on a
communications channel. It is often referred to as Bits per second (BPS) which is
technically inaccurate but widely accepted.
- BBS - Bulletin Board System.
- Bit - Binary Digit. A single basic computer signal consisting of a value of 0 or 1, off
- Buffer - A memory area used for temporary storage during input/output operations.
- Bulletin Board System - A host system, into which callers may dial with their modems to
read and send electronic mail, upload and download files, and chat online with other
- Byte - A group of Bits acted upon as a group, which may have a readable ASCII value as a
letter or number or some other coded meaning to the computer. It is commonly used to refer
to 8-bit groups. 1 kilobyte = 1,024 bytes; 64K = 65,536 bytes or characters.
- Carrier - A continuous frequency capable of being either modulated or impressed with
another information-carrying signal. Carriers are generated and maintained by modems via
the transmission lines of the telephone companies.
- Conference - An area of public messages on a Bulletin Board System, usually with a
particular topic and, often, a conference host or moderator to guide the discussion. Also
called Folder, SIG (for "Special Interest Group") or Echo.
- CCITT - A French acronym for the International Telephone and Telegraph Consultative
Committee. This international organization defines the standards for telephone equipment
such as the Bell 212A standard for 1200 baud, CCITT V.22 for 2400 baud and CCITT V.32 for
- CPS - Characters Per Second. A transfer rate estimated from the bit rate and length of
each character. If each character is 8 bits long and includes a start and stop bit for
Asynchronous transmission, each character needs 10 bits to be sent. At 2400 baud it is
transmitted at approximately 240 CPS.
- CRC - Cyclical Redundancy Check. An error-detection technique consisting of a cyclic
algorithm performed on each "block" of data at the sending and receiving end of
the transmission. As each block is received, the CRC value is checked against the CRC
value sent along with the block. Many protocols including XMODEM- CRC and ARQ will request
a resend until the block is received correctly.
- Download - Receiving a file from a Bulletin Board System, using a terminal program (for
example QModem) and a transfer protocol (for example Zmodem).
- DTE - Data Terminal Equipment. The device that is the originator or destination of the
data sent by a modem.
- DTR - Data Terminal Ready. A signal generated by most modems indicating a connection
between the DTE (computer) and the modem. When DTR is "high" the computer is
- Data Compression Protocols - Compression of data by the modem allows more information to
be transferred in a shorter time frame. Protocols for data compression include CCITT
V.42bis and MNP 5.
- Data Transmission Protocols - These are standards for modulation and transmission of
data at various speeds. The standards are Bell 103 & V.21 for 300bps, Bell 212A &
V.22 for 1200bps, V.22bis for 2400bps, V.32 for 9600bps and V.32 bis for 14,400bps.
Proprietary protocols are also used extensively for higher baud rates.
- Echomail - Public Message Conferences on a Bulletin Board System which are shared and
distributed among other Bulletin Boards as part of an Echomail Network.
- Expanded Memory - Extra memory (above 640k) on your XT or AT-compatible computer, which
is installed with an EMS driver, and may be used by some programs to store data.
- Extended Memory - Extra memory (above 640k) on your 80286 or 80386 compatible computer.
Not normally usable by DOS applications, but may be configured as a virtual drive or a
disk cache on an 80286 computer, or as Expanded Memory on an 80386 computer.
- Flow Control - A mechanism that compensates for differences in the flow of data to and
output from a modem or computer. Either hardware or software can be used for this control
to prevent data loss. Hardware flow control using the modem makes use of a buffer to store
data to be sent and data received. Flow control is necessary if the Communications port is
locked at a higher rate than the connection rate.
- Error Control Protocols - These are various modem-based techniques which check the
reliability of characters or blocks of data at a hardware level. Examples include MNP 2-4,
- Freeware - Computer software which may be distributed on Bulletin Board Systems, and for
which the author requests no license fee or registration fee.
- Full Duplex - Signal flow in both directions at the same time. It is sometimes used to
refer to the suppression of online LOCAL ECHO and allowing the remote system to provide a
- Half Duplex - Signal flow in both directions, but only one way at a time. It is
sometimes used to refer to activation of LOCAL ECHO which causes a copy of sent data to be
displayed on the sending display.
- Host System - Another name for a Bulletin Board System (BBS)
- Local Area Network (LAN) - A group of computers joined with cables and software,
allowing hard disks and other devices to be shared among many users.
- Mail Door - A subsection of a Bulletin Board System which creates .QWK mail packets.
- MNP - Microcom Networking Protocol. A set of hardware error protection protocols (MNP
levels 1 - 4) and data compression techniques (MNP level 5) developed by Microcom, now in
the public domain. It makes use of CRC and retransmission of defective blocks by checking
performed within the modem.
- Netmail - Private electronic mail which is transmitted by a user calling one Bulletin
Board System to another user calling a different Bulletin Board System.
- NRAM - Nonvolatile Random Access memory. A user-programmable memory chip whose data is
retained when power to the chip is turned off. NRAM is used in many modems to store
- ON/OFF Hook - A descriptive term referring to manually lifting a telephone receiver
(taking it OFF Hook) and replacing it (going ON Hook). OFF Hook produces a busy signal on
the phone line.
- Packer - A program to compress multiple files into a single file, such as PKZIP, ARC or
- Packet - A mail packet (with a .QWK extension) from a host system
- Parity - An error detection method used in both communications and computer memory
checking to determine character validity. Communications now makes use of more efficient
"block" checking although parity must still be matched in a communication
session for transfer to take place correctly. Host communication in the BBS environment
omits parity checking (no parity).
- Protocol - A system of rules and procedures governing communications between two
devices. File transfer protocols in your communications program refer to a set of rules
governing how error checking will be performed on blocks of data.
- Public Domain - Computer software on which no copyright exists (usually by a specific
statement to that effect by the author), and which may be freely used and distributed.
- Remote Echo - A copy of the data being received is returned to the sending system for
display on the screen. See Full/Half duplex.
- Shareware - Computer software which is distributed on the "Honor System",
which may be freely copied and distributed, but for which a registration fee or payment is
required for continued use beyond an initial evaluation period.
- SysOp - The SYStem OPerator of a Bulletin Board System. The person responsible for
setting up and maintaining the BBS.
- Thread - A group of BBS messages and replies linked and sorted by topic.
- Unpacker - A program to uncompress a file from a Packer
- Upload - To transfer a file from your computer to another computer, using your terminal
program (for example Qmodem) and a transfer protocol (for example Zmodem)
- V.21 - CCITT standard for modem communications at 300bps. Modems made in the US follow
the Bell 103 standard.
- V.22 - CCITT standard for modem communications at 1200bps, compatible with the Bell 212A
standard used in the US and Canada.
- V.22 bis - CCITT standard for modem communications at 2400bps. It includes automatic
fallback to 1200bps and compatibility with Bell 212A and V.22 modems.
- V.23 - CCITT standard for modem communications at 1200bps with a 75bps back channel. It
is used in the United Kingdom.
- V.32 - CCITT standard for modem communications at 4800 and 9600bps. It includes
automatic fallback to 4800 when line quality is poor.
- v.34 -CCITT standard for modem communications at 28,800bps
- V.32 bis - CCITT standard for modem communications at 14,400bps with automatic fallback
to 12,000, 9600, 7200 and 4800bps. As line quality improves communications speed can also
be increased to the next higher rate.
- V.42 - CCITT standard for modem communications that defines negotiation for LAPM error
control. V.42 also includes support for MNP error correction protocol levels 1 - 4.
- V.42 bis - CCITT extension of V.42 that adds data compression to the V.42 correction