Glossary Section "U" ( Definitions )
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U-interface A twisted pair
subscriber loop that connects the NT1 reference point to the ISDN network, as defined in
the 1.411 Recommendation. This interface provides Basic Rate Access with an operating
frequency of 160 kbps and an information rate of 144 kbps. Under U.S. regulations, this
also marks the line of demarcation between customer-owned equipment and the public
UA User Agent. An OSI
application process that represents a human user or organization in the X.400
Message Handling System. Creates, submits, and takes delivery of messages on the user's
UART The Universal
Asynchronous Receiver-Transmitter (UART) is an integrated circuit that contains the
software programming control of the PC serial port.
UBR Unspecified Bit Rate. An
ATM service type in which the ATM network makes a "best effort" to meet the
transmitter's bandwidth requirements; essentially a "send and pray" service like
that available from today's networks.
UDP User Datagram Protocol. A
transport protocol in the Internet suite of protocols. UDP, like TCP, uses IP for
delivery; however, unlike TCP, UDP provides for exchange of datagrams without
acknowledgments or guaranteed delivery.
UKERNA UK Education and
Research Networking Association. See JANET, Super-JANET.
UNI User Network Interface is a demarcation point between the user and the service provider.
URL Uniform Resource Locator.
An identifier which describes the location of a particular piece of information
("document") including the protocol used to retrieve that information. For
USB Universal Serial Bus
USENET A collection of
thousands of topically named newsgroups, the computers which run the protocols, and the
people who read and submit USENET news. Not all Internet hosts subscribe to USENET and not
all USENET hosts are on the Internet.
UTP Unshielded Twisted Pair.
Generic term for "telephone" wire used to carry data such as l0Base-T and
l00Base-T. Various categories (qualities) of cable exist certified for different kinds of
UUCP UNIX to UNIX Copy
Program. A protocol used for communication between consenting UNIX systems. Somewhat
historic as most UNIX systems today communicate using the TCP/IP protocol suite.
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