Browsing: U
|
|
|
UART |
Universal Asynchronous
Receiver/Transmitter. Integrated circuit, attached to the
parallel bus of a computer, used for serial communications. The UART
translates between serial and parallel signals, provides
transmission clocking, and buffers data sent to or from the
computer. |
|
UB Net/One |
Ungermann-Bass Net/One.
Routing protocol, developed by UB Networks, that uses hello packets
and a path-delay metric, with end nodes communicating using the XNS
protocol. There are a number of differences between the manner in
which Net/One uses the XNS protocol and the usage common among other
XNS nodes.
|
|
UBR |
Unspecified bit rate.
QOS class defined by the ATM Forum for ATM networks. UBR allows any
amount of data up to a specified maximum to be sent across the
network, but there are no guarantees in terms of cell loss rate and
delay. Compare with
ABR
(available bit rate),
CBR,
and VBR.
|
|
UDP |
User Datagram Protocol.
Connectionless transport layer protocol in the TCP/IP protocol
stack. UDP is a simple protocol that exchanges datagrams without
acknowledgments or guaranteed delivery, requiring that error
processing and retransmission be handled by other protocols. UDP is
defined in RFC 768.
|
|
UL |
Underwriters Laboratories.
Independent agency within the United States that tests product
safety.
|
|
ULP |
Upper-layer protocol.
Protocol that operates at a higher layer in the OSI reference model,
relative to other layers. ULP is sometimes used to refer to the
next-highest protocol (relative to a particular protocol) in a
protocol stack.
|
|
unbalanced configuration |
HDLC configuration with one primary
station and multiple secondary stations.
|
|
Underwriters Laboratories |
See
UL.
|
| Ungermann-Bass
Net/One |
See
UB
Net/One.
|
| UNI |
User-Network Interface.
ATM Forum specification that defines an interoperability standard
for the interface between ATM-based products (a router or an ATM
switch) located in a private network and the ATM switches located
within the public carrier networks. Also used to describe similar
connections in Frame Relay networks. See also
NNI,
Q.920/Q.921
and SNI
(Subscriber Network Interface).
|
| unicast |
Message sent to a single network
destination. Compare with
broadcast
and multicast.
|
| unicast address |
Address specifying a single network
device. Compare with
broadcast
address and
multicast
address. See also
unicast.
|
| uninsured traffic |
Traffic within the excess rate (the
difference between the insured rate and maximum rate) for a VCC.
This traffic can be dropped by the network if congestion occurs. See
also CLP,
insured
rate, and
maximum
rate.
|
| unipolar |
Literally meaning one polarity, the
fundamental electrical characteristic of internal signals in digital
communications equipment. Contrast with
bipolar.
|
| unity gain |
In broadband networks, the balance
between signal loss and signal gain through amplifiers.
|
| Universal Asynchronous
Receiver/Transmitter |
See
UART. |
| Universal Resource Locator |
See
URL.
|
| UNIX |
Operating system developed in 1969 at
Bell Laboratories. UNIX has gone through several iterations since
its inception. These include UNIX 4.3 BSD (Berkeley Standard
Distribution), developed at the University of California at
Berkeley, and UNIX System V, Release 4.0, developed by AT&T.
|
| UNIX-to-UNIX Copy Program |
See
UUCP.
|
| unnumbered frames |
HDLC frames used for various control
and management purposes, including link startup and shutdown, and
mode specification.
|
| unshielded twisted-pair |
See
UTP.
|
| unspecified bit rate |
See
UBR.
|
| UPC |
Usage parameter control.
See traffic
policing.
|
| upper-layer protocol |
See
ULP.
|
| UPS |
Uninterruptable power supply.
Backup device designed to provide an uninterrupted power source in
the event of a power failure. They are commonly installed on all
file servers and wiring hubs.
|
| Urgent Pointer |
Indicates the end of the urgent data.
|
| URL |
Universal Resource Locator.
Standardized addressing scheme for accessing hypertext documents and
other services using a WWW browser. See also
WWW
browser.
|
| usage parameter control |
See
traffic
policing.
|
| USENET |
Initiated in 1979, one of the oldest
and largest cooperative networks, with over 10,000 hosts and a
quarter of a million users. Its primary service is a distributed
conferencing service called news.
|
| User Datagram Protocol |
See
UDP.
|
| User-Network Interface |
See
UNI.
|
| UTP |
Unshielded twisted-pair.
Four-pair wire medium used in a variety of networks. UTP does not
require the fixed spacing between connections that is necessary with
coaxial-type connections. There are five types of UTP cabling
commonly used:
Category
1 cabling,
Category
2 cabling,
Category
3 cabling,
Category
4 cabling, and
Category
5 cabling. Compare with
STP.
See also EIA/TIA-586
and twisted
pair.
|
| UUCP |
UNIX-to-UNIX Copy Program.
Protocol stack used for point-to-point communication between UNIX
systems.
|
