Multitech CommPlete MT5634HD8, User Manual, Page: 91 / 99

Glossary
CommPlete Communications Server 85
V.42bis : A CCITT recommendation for data
compressing hardware on a modem that accepts
asynchronous input. V.42bis is based on a
dynamically updated dictionary that looks up
common strings and replaces the strings with
code words. This reduces the amount of
characters actually transmitted. V.42bis has
been found to be most effective for file transfers
that contain long strings of repetitive
information and least effective for short strings
of unique data.
V.54 : The CCITT recommendation to
standardize Bit Error Rate Testing (BERT) and
Loopback testing (Local Analog and Digital
Loopback, as well as Remote Analog and
Digital Loopback).
VRC (Vertical Redundancy Check ): An error
checking method that generates and tests a
parity bit for each byte of data that is moved
or transmitted.
W
WATS (Wide Area Telephone Service) : A
discounted long-distance calling plan that
allows calls in or out. The popular 800 numbers
are WATS lines in. The calls are charges to the
holder of the 800 number at a discounted rate.
Workstation : Traditionally a dumb terminal
connected to a host. However, with the advent
of LANS and WANS, PCs that are connected to
a LAN are now called workstations too, even
though they are capable of independent
processing. A workstation is simply an
input/display device through which a user
accesses a resource.
X
X.121 : CCITT’s recommendation for unique
addressing of each DTE connected to a
communications network throughout the world.
X.121 uses fifteen digits: a one-digit prefix, a
four-digit DNIC number (which identifies the
country and PDN), and a ten-digit national
terminal number.
X.21 : CCITT’s recommendation for a 15-pin,
digital interface. It is not widely accepted,
because of the analog loops still prevalent in
data communications. For this reason, CCITT
introduced the X21bis standard for use with
synchronous modems.
X.25 : CCITT’s definition of a three-level
packet-switching protocol to be used between
packet-mode DTEs and network DCEs. X.25
corresponds with the lower three/four layers of
the seven layer OSI model.
X.28 : CCITT’s definition of asynchronous
commands used by a local ASCII terminal to
configure an X.25 PAD.
X.29 : CCITT”s definition of packetized
commands sent to configure a remote PAD via an
X.25 link.
XModem : A widely used asynchronous file
transfer protocol. Programs typically use both
the older version, checksum, and the new
version, CRC method, to detect errors. If CRC is
not present at the other end of a file transfer,
then it will use checksum.
Y
YModem : An asynchronous file transfer
protocol that improves speed by transmitting
1,024-byte (1K) blocks and batch file transfer.
Z
ZModem : An asynchronous file transfer
protocol that is more efficient than XModem. It
sends file name, date and size first, and
responds well to changing line conditions due to
its variable length blocks. It uses CRC error
correction and is effective in delay-induced
satellite transmission.