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Glossary
61202.086L1-1 ISU 512 User Manual 105
V.35
CCITT standard for trunk interface between a network access device and a packet net-
work that defines signaling for data rates greater than 19.2 kbps.
videoconferencing
The real-time, usually two-way, transmission of digitized video images between
two or more locations. Teleconferencing requires a wideband transmission facili-
ty. Transmitted images may be freeze-frame (where television screen is repainted
every few seconds to every 20 seconds) or full motion. Bandwidth requirements
for two-way videoconferencing range from 6 MHz for analog, full-motion, full-col-
or, commercial grade TV to 56 kbps for digitally-encoded freeze-frame to 1.544
kbps for very good quality, full-color, full-motion TV.
XMODEM
An error-correcting file transfer, data transmission protocol used to transmit files
between PCs. The XMODEM protocol sends information in 128 byte blocks of da-
ta. Some sums (check sums) are done on each block and the result is sent along
with the block. If the result does not check out at the other end, the computer at
the other end sends a request (a NAK - negative acknowledgment) to retransmit
that block once again. If the block checks out, the computer sends ACK (an ac-
knowledgment). In this way, relatively error-free transmission can be accom-
plished.