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Glossary Section "U" ( Definitions )

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0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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 network.

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 behalf.

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 example:   http://www.bestdatasource.com

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 networking technologies.

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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