U

UDP/IP

See User Datagram Protocol/Internet Protocol.

UHTTP

See Unidirectional Hypertext Transfer Protocol

unicast

A point-to-point networking model in which a packet is duplicated for each address that needs to receive it. See also multicast.

Unidirectional Hypertext Transfer Protocol

(UHTTP) A protocol designed to deliver data in a one-way-only environment such as IP multicasting. The UHTTP protocol has mechanisms for forward error correction and for the reordering of packets upon arrival at a broadcast client. ATVEF-compliant enhanced television broadcasts use UHTTP for resource transfers.

upstream

One-way data flow from broadcast client to head end. See also downstream.

User Datagram Protocol/Internet Protocol

(UDP/IP) A networking protocol used to send large unidirectional packets across interconnected networks made up of computers with diverse hardware architectures and operating systems. The UDP portion of the protocol, a networking layer above IP, is used to send unidirectional packets of up to 64 kilobytes in size and includes standards for routing data within a single computer so it reaches the correct client application. The IP portion of the protocol includes standards for how computers communicate and conventions for connecting networks and routing traffic. See also Transmission Control Protocol/Internet Protocol.

user mode

Software processing that occurs at the application layer, ring 3.

utility filter

A filter that supports the processing of audio and video without necessarily directly manipulating the broadcast stream. See also renderer filter, source filter, transform filter.