Multitech RouteFinder MTASR2-203, Руководство пользователя, Страница: 88 / 90

RouteFinder-T1 User Guide
MTASR2-203 88
U
UART (Universal Asynchronous Receiver/Transmitter) (pronounced “you art”): A chip that transmits and receives
data on the serial port. It converts bytes into serial bits for transmission, and vice versa, and generates and strips the
start and stop bits appended to each character.
User Datagram Protocol (UDP): A TCP/IP protocol describing how messages reach application programs within a
destination computer. This protocol is normally bundled with IP-layer software. UDP is a transport layer, connectionless
mode protocol, providing a (potentially unreliable, unsequenced, and/or duplicated) datagram mode of communication for
delivery of packets to a remote or local user.
UNIX: An operating system developed by Bell Laboratories that features multiprogramming in a muti-user environment.
Unshielded Twisted Pair (UTP): Telephone-type wiring. Tansmission media for 10Base-T.
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 64K bps unrestricted user data (allowing all 0s in the
user data). An alternative to (but not as popular as) B8ZS.