Multitech MultiModem MT4X56USB User Manual page 92

MultiModemUSB User Guide
USB: See Universal Serial Bus.
USBD: See Universal Serial Bus Driver.
USB Performance categories: Low Speed (Interactive Devices at 10-100 Kb/s); Medium Speed (Phone, Audio,
Compressed Video at 500Kb/s - 10Mbp/s); High Speed (Video, Disk at 25-500 Mb/s)
V
V.25bis: An ITU-T standard for synchronous communications between a mainframe or host and a modem using HDLC or
other character-oriented protocol.
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.
92 MT4X56USB