 some type of peripheral device, often a printer, in a series of bits in which each bit is sent one at a time as part of a sequence. Video Communication: the Whole Picture server In a network, a server is the device that host applications and allocates the activities of shared support resources. Servers store applications, files, and databases; they provide access to printers and fax machines, and they permit clients to access external communications networks and information systems. Session Description Associated with SIP, SDP is a Protocol for conveying Protocol information about streams in multimedia sessions to enable recipients of a session description to participate in a session. In a Multicast session, SDP is a means to communicate the timing and existence of a session, and to convey sufficient information to enable recipients to join and participate in the session. Session Initiation Protocol Defined in IETF RFC 2543, SIP is an application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants. Sessions can be Internet multimedia conferences, Internet telephone calls, or multimedia distribution. Members in a session can communicate via multicast, a mesh of unicast relations, or a combination of these. set-top box In a CATV environment, the cable terminates in the subscriber's location on a decoder or set-top box, which is connected directly to the television receiver. Set-tops vary greatly in complexity. Older models merely translate the frequency received off the cable into a frequency suitable for the television receiver; newer models are addressable and offer a unique identity much like a telephone. Interactive set-tops allow subscribers to communicate interactively. seven-layer model See OSI (Open Systems Interconnection) model. shadow mask In a color monitor, this component is placed between the electron guns and the screen to ensure that the electron beams are restricted to their targeted dots. shutter A device that cuts off light in an opt