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MultiModemZPX User Guide
V.54: The ITU-T standard for local and remote loopback tests in
modems, DCEs and DTEs. The four basic tests are:
• local digital loopback (tests DTE send and receive
circuits),
• local analog loopback (tests local modem operation),
• remote analog loopback (tests comm link to the
remote modem), and
• remote digital loopback (tests remote modem
operation).
Virtual Circuit: A logical connection. Used in packet switching
wherin a logical connection is established between two devices
at the start of transmission. All information packets follow the
same route and arrive in sequence (but do not necessarily
carry a complete address).
W
Wide Area Network (WAN): 1. A network that provides
communication services to a geographic area larger than that
served by a local area network or a metropolitan area network,
and that may use or provide public communication facilities. 2.
A data communications network designed to serve an area of
hundreds or thousands of miles; for example, public and private
packet-switching networks, and national telephone networks.
Contrast with local area network (LAN).
Wide Area Telecommunications Service (WATS): A low-cost
toll service offered by most long distance and local phone
companies. Incoming (800 call service, or IN-WATS) and
outgoing WATS are subscribed to separately, but over the same
line.
X
X.25: ITU-T’s definition of a three-level packet-switching
protocol to be used between packet-mode DTEs and network
DCEs. X.25 corresponds with layer 3 of the 7-layer OSI model.
Y
Yellow Alarm: An error indication sent by the T1 device when it
has not gotten a receive signal, or cannot synchronize on the
receive signal received. Contrast “Red Alarm” and “Blue Alarm”.
Z
Zero Byte Time Slot Interchange (ZBTSI): A method for
allowing 64 Kbps unrestricted user data (allowing all 0s in the
user data). An alternative to (but not as popular as) B8ZS.