Glossary of terms for laptop and notebook modems.

analog data - Continuously variable data. (Compare with digital data.)

answer mode - The mode in which the modem is set to answer the phone.

ASCII - An acronym for American Standard Code for Information Interchange (pronounced as' kee). ASCII is a code where the alphabet, the digits 0-9, punctuation marks, special characters and control characters are represented by the numbers 0-127. It's used as a standard to transfer text between computing devices.

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asynchronous - Not synchronized by a clocking signal; in code sets. When communications aren't paced by a clock, it's necessary to add start and stop bits to the characters.

auto answer - Same as "answer mode."

baud - The speed, measured in signals per second, at which two modems communicate. Since each signal can represent more than one bit, don't confuse baud with bits per second (bps).

bit - The smallest unit of digital information, one of two possible states. Those two states are normally represented by the digits "0" and "1".

bps - Stands for "bits per second" and refers to the rate at which information is transmitted. Not to be confused with baud rate.

CCITT - Stands for "Comité Consultatif International Télégraphique et Téléphonique", an international organization which devises recommendations for international telecommunications, and establishes standards.

command - A directive from the user to the computer to perform an immediate action.

configuration - Variable modem characteristics that must be set properly for a modem to communicate with a computer or another modem.

data - Any type of information which a computer can process, such as numbers, letters or symbols.

data compression - The reduction of data by removing repetitive data or place holders and replacing them with shorter strings of data in order to reduce the size of a file. This is done in such a way that the original data can later be restored to the file with little or no loss of integrity.

digital data - A discontinuous signal whose various states are discrete intervals apart. (Compare to analog data.)

echo - A signal sent back to the originating device for display or verification.

error control - A process where data is broken down into blocks, and then a checksum is calculated. The checksum is transmitted with the data for the receiving computer to verify the integrity of the data.

flow control - Signalling between computers where pauses in data transmission pace the data received.

full duplex - A four wire telecommunication circuit allowing simultaneous two-way transmission.

handshaking - A protocol for modems to indicate when to start and stop transmitting, and other information about the connection.

ITU-T - Stands for International Telecommunications Union, Telecommunication Standardization Sector. This is the group that's responsible for setting the standards for telephone, data and fax communications. They used to be known as CCITT, but on March 1, 1993 they changed their name.

MNP - Microcom Networking Protocol. Error protocols = MNP Class 2-4; Data Compression protocols = MNP Class 5.

modem - Modulates and demodulates serial information to tones and back for transmission over phone lines.

parity/parity bit - A check bit added after a group of binary digits as a method of detecting errors in data transmission. Always odd, or always even. Not supported by some computers due to higher quality phone lines.

PCMCIA - (also called PC Card) An acronym that stands for Personal Computer Memory Card International Association, a nonprofit trade association that has set up standards for personal computer input/output slots that will accept small credit card size devices which can contain anything from additional random access memory to fax/modems to network cards. For some time now, PCMCIA slots have been appearing on almost all new portable computers as well as many of the pocket-sized personal digital assistants.

protocol - The convention between two modems/computers regarding the form/content of the information they exchange.

register/status register - An S-register is a part of memory in a modem where information is stored, and retrieved during operation to perform certain functions.

RS-232-C - A serial-type connection, both physical and electrical, between computers and modems. (Electronics Industries Association [EIA] standards.)

serial communication - Transmits data one bit at a time over one wire; vs. parallel communication which transmits several bits at a time over several wires.

stop bit - The last element (bit) of a character in a character set designed for asynchronous communications.

synchronous - Timed by a clocking signal. Incoming data is synchronized with a clocking signal to eliminate the need for start and stop bits.

throughput - The total amount of data received per second after it's uncompressed. The actual connection rate might only be 14,400 bits per second. However, if 57,600 bits of data can be compressed down to 14,400 bits (a typical 4:1 compression scheme), then they can be sent in one second and expanded back into 57,600 bits at the other end. In this example, the actual data transmission rate was 14,400 bps, but the throughput was 57,600 bps.

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