in which the image appears as pixel blocks. Can be caused by compression when the sampling rate or bandwidth is not adequate to fully describe the original image. time-division multiplexing A way of enabling a single bearer signal to carry more than one information channel simultaneously. This is achieved by sharing the common transmission path on a cyclical basis. Each channel takes a turn using the path by entering the source data into a "time slot." Common TDM systems can support 24 channels in the US and 32 in Europe. time slot In TDM or TDSW, the slice of time that belongs to a digitized communication whether it be voice, data or video communication. transcoding Conversion from one format to another. This may be from one digital format into another, or between dissimilar formats such as from digital frames into analog video or from text into speech. transform coding A technique of video compression that requires VLSI chips with hundreds of thousands of gates. See DCT for a description of one type of transform coding. Video Communication: the Whole Picture TransMux MPEG-4 specifies an interface to the TransMux (Transport Multiplexing) models, the layer that offers transport services for matching the requested QoS. Any suitable existing transport protocol stack (e.g., RTP in UDP/IP, AAL5 in ATM, or Transport Stream in MPEG-2) over a suitable link layer may become a specific TransMux instance. transponder A microwave repeater mounted on a satellite and used to receive communication from an uplink and retransmit it at a different frequency on a downlink. tree and branch A cable television arrangement in which large capacity cables called super trunks radiate from the head-end to various sectors of the franchise area to hub sites. From these hub sites, lower-capacity cables branch out into the surrounding districts to be split and split again until cable runs along every street. A tapping point outside each residence enables the final connection to the residence. tuner A piece of equipment or portion of a circuit