3Com 56K manual Glossary

2GLOSSARY

dynamically reverse the channels during a call if the volume of data transfer changes.

asynchronous Data transmission in which the length of time between transmitted transmission characters may vary.

Because the time lapses between transmitted characters are not uniform, the receiving modem must be signaled as to when the data bits of a character begin and when they end. The addition of start and stop bits to each character serves this purpose.

auto answer A feature in modems enabling them to answer incoming calls over the phone lines without the use of a telephone receiver.

auto dial A feature in modems enabling them to dial phone numbers over the phone system without the use of a telephone transmitter.

Automatic Repeat A general term for error control protocols which feature error detection Request (ARQ) and automatic retransmission of defective blocks of data. See HST,

MNP, and V.42.

baud rate The number of discrete signal events per second occurring on a communications channel. Although not technically accurate, baud rate is commonly used to mean bit rate.

binary digit (bit) A 0 or 1, reflecting the use of a binary numbering system (only two digits). Used because the computer recognizes either of two states, OFF or ON. Shortened form of binary digit is bit.

bit See binary digit.

bit-mappingA technique that lets one decimal number (in this case, a number between 0 and 255) stand for up to 8 separate binary settings.

bit rate The number of binary digits, or bits, transmitted per second (bps). Communications channels using telephone channel modems are established at set bit rates, commonly 300, 1200, 2400, 4800, 9600, 14400, and 28800.

bps The bits (binary digits) per second rate.

buffer A memory area used as temporary storage during input and output operations. An example is the modem's command buffer. Another is the Transmit Data flow control buffer used for flow control and to store