U

UBR (Unspecified Bit Rate) Level: 3 Definition: A type of traffic on an ATM network that is not considered time critical, UBR data is transferred with an unspecified bit rate using whatever bandwidth is available at any given time. In this sense, UBR transmissions are similar to IP service. UBR traffic is given a “best effort” priority in an ATM network. (See also ABR, CBR, and VBR.)

UDDI (Universal Description, Discovery, and Integration) Level: 3 Definition: UDDI is an open framework for describing or listing services on the Internet. Based on the W3C’s XML standard and closely integrated with SOAP, UDDI provides three types of listings: White Pages, which include address, contact, and other known identifiers; Yellow Pages, which include industrial categorizations based on standard taxonomies; and Green pages, which include information about the technical means to access services offered by a particular company. (See also SOAP and XML.)

UHF (Ultra High Frequency) Level: 2 Definition: The portion of the radio frequency spectrum ranging between 300 MHz and 3 GHz. The UHF band is used for transmission of television broadcast channels 14 through 67. Previously allocated television channels 68 through 83 have been reassigned for use as cellular telephone services, except for a few special cases. TV channels 52 through 69 are to be auctioned for other

to is also used for communication and for cordless telephones. (See also DTV and Spectrum.)

UI (See User Interface.)

Ultra Extended Graphics Array (See UXGA.)

Ultra High Frequency (See UHF.)

Underscanning Level: 3 Definition: The process of decreasing the horizontal and vertical size of an image permitting the view of the entire video picture, including sync and blanking. Many professional TV monitors have an underscan button or switch to allow for viewing the entire TV picture. On a television screen, underscanning allows viewing of skew and tracking that would not be visible in normal (overscanned) mode. Underscanning is also helpful when aligning test charts to be certain they touch all four corners of the raster. Likewise, when checking the alignment of multiplexer images from a film chain underscan allows proper framing of the projected image going into the video camera. Underscanning is also useful on a computer monitor, where a user might want to make sure that all display information around the fringe will be shown (such as the Start button in the Windows operating system). (See also Overscan.)

UNI (User Network Interface) Level: 3 Definition: A telephone industry protocol used to define the point at which the private subscriber and the public network meet. This protocol includes such items as signaling, addressing, and traffic management.