USRobotics V.34 user manual Dce

COURIER HIGH SPEED MODEMS

Cyclic Redundancy Checking (CRC)

An error-detection technique consisting of a cyclic algorithm performed on each block or frame of data by both sending and receiving modems. The sending modem inserts the results of its computation in each data block in the form of a CRC code. The receiving modem compares its results with the received CRC code and responds with either a positive or negative acknowl- edgment. In the ARQ protocol implemented in U.S. Robotics high speed modems, the receiving modem accepts no more data until a defective block is received correctly.

Data Communications

A type of communications in which computers and terminals are able to exchange data over an electronic medium.

Data Compression

When the transmitting modem detects redundant units of data, it recodes them into shorter units of fewer bits. The receiving modem then decompresses the redundant data units before passing them to the receiving computer.

Data Compression Table

A table of values assigned for each character during a call under data compression. Default values in the table are continually altered and built during each call: the longer the table, the more efficient throughput gained.

If a destructive Break is sent during a call (see the &Y com- mand), causing the modems to reset the compression tables, you can expect diminished throughput.

Data Mode

The mode in which the fax modem is capable of sending and receiving data files. A standard modem without fax capabilities is always in Data mode.

DCE

Data Communication (or Circuit-Terminating) Equipment. In this manual, the term applies to dial-up modems that establish and control the data link via the telephone network.

Glossary J-5