IBM Nways 2216, Руководство по обслуживанию и ремонту

Страница: 160 / 168

Trivial File Transfer Protocol (TFTP). In the Internet
suite of protocols, a protocol for file transfer that
requires minimal overhead and minimal capability.
TFTP uses the connectionless datagram delivery
services of the User Datagram Protocol (UDP), which
allows hosts that have no disk storage to implement
TFTP in read-only memory (ROM) and use it to boot
themselves.
U
UDP. User Datagram Protocol.
UNI. User network interface (protocol).
UTP. Unshielded twisted pair.
V
V ac. Volts alternating current.
V.24. In data communications, a specification of the
CCITT that defines the list of definitions for interchange
circuits between data terminal equipment (DTE) and
data circuit-terminating equipment (DCE).
V.25. In data communications, a specification of the
CCITT that defines the automatic answering equipment
and parallel automatic calling equipment on the General
Switched Telephone Network, including procedures for
disabling of echo controlled devices for both manually
and automatically established calls.
V.35. In data communications, a specification of the
CCITT that defines the list of definitions for interchange
circuits between data terminal equipment (DTE) and
data circuit-terminating equipment (DCE) at various data
rates.
V.36. In data communications, a specification of the
CCITT that defines the list of definitions for interchange
circuits between data terminal equipment (DTE) and
data circuit-terminating equipment (DCE) at rates of 48,
56, 64, or 72 kilobits per second.
version. A separately licensed program that usually
has significant new code or new function.
virtual circuit. (1) In packet switching, the facilities
provided by a network that give the appearance to the
user of an actual connection. (T) See also
data circuit.
Contrast with physical circuit. (2) A logical connection
established between two DTEs.
virtual connection. In frame relay, the return path of a
potential connection.
VPD. Vital product data.
W
WAN. Wide area network.
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. (T) (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) and metropolitan area network (MAN).
X
X.21. An International Telegraph and Telephone
Consultative Committee (CCITT) recommendation for a
general-purpose interface between data terminal
equipment and data circuit-terminating equipment for
synchronous operations on a public data network.
X.25. An International Telegraph and Telephone
Consultative Committee (CCITT) recommendation for
the interface between data terminal equipment and
packet-switched data networks. See also
packet
switching.
X-10
2216 Maintenance Manual