ponents such as monitors, speakers, and printers that receive a computer's data. Video Communication: the Whole Picture P frame Predictive framing, as specified in the MPEG Recommendation. Pictures are coded by predicting a current frame using a past frame. The picture is broken up into 16x16 pixel blocks. Each block is compared to a the block that occupies the same vertical and horizontal position in a previous frame. packet A unit of digital data that is switched as a unit. A packet consists of some number of bits (either a fixed number or a variable number), such as those that serve as an address. The packet can be sent over a packet switching network by the best available route (switched virtual circuit) or over a predetermined route (permanent virtual circuit). In a switched virtual circuit or TCP/IP networking environment packets from a single message may take many different routes. At the destination they are reunited with other packets that comprise the communication, re-sequenced and presented to the recipient in their original form. packet switching A technique for transmitting data in which the message is subdivided into smaller units called packets. These packets each carry the destination address and sequencing information. Packets from many users are then collated on a single communications channel. Phase Alternate Line. The television standard used in most of Western Europe except France. PAL is not a single format however; variations are used in Australia/New Zealand, China, Brazil, and Argentina. PAL uses an image format composed of 625 lines. Frames are sent at a rate of 25 per second and each frame is divided into two fields to accommodate Europe's 50 Hz electrical system. PAL uses YUV, a trichromatic color system. To pivot a camera in a horizontal direction. parallel communications A multi-wire or bus system of communications. The bits that make up the information are transmitted separately, each assigned to a separate wire in the cable. Parallel communications are used frequently in computer-