ch latency is tolerable. In voice and video communications, a constant bit rate is required for smooth delivery. RTP's approach is to give low-latency connection-oriented communications a higher priority than connectionless data. RTP also addresses the need for multicasting and compression over the Internet and other TCP/IP-based networks. TCP is a reliable transport, but its efforts on behalf of reliability are not ideal for video communications. TCP re-sends packets of data that have not been properly received. In video communications, packets that do not arrive on time are no longer useful. RTP does not resend missed packets, but notifies a server that a packet was missed. If the missed packets threshold reaches a specified level, RTP can request additional bandwidth allocation. redundant In the context of compression, redundant information is that which does not change over time (temporal) or space (spatial). Temporal redundancy manifests in a sequence of video frames in which successive frames contain the same information as those that preceded them. This information is, thus, redundant; e.g., not necessary to convey. Rather, it is only necessary to convey the areas of the frame that didchange for that information is critical to the recipient's accurate interpretation of the new frame. Spatial redundancy manifests within a frame of video in which a group of Glossary of Terms similar pixels are clustered. The goal of video compression is to eliminate redundancy that, in turn, reduces the data rate required for transmission. reference frames In video compression reference or intra-coded frames are sent periodically to eliminate the accumulated errors generated through the process of interframe coding. refresh To recharge the cells of a volatile digital memory SO that their contents are not lost. Alternately, to "paint" a new picture on the screen of a VDT is to refresh the screen. repeater A device used to reprocess and amplify a weak signal in a transmission system. Used where the distance between the sender 