3.1) Adaptive update.
A set of rectangles of pixel data makes a frame buffer update. An update is a change from one valid frame buffer state to another. In this sense an update is similar to a frame of video. It differs; however in that it usually affects only small area of the framebuffer.Each rectangle may be encoded using a different scheme. The server can therefore choose content encoding, most appropriate for a particular screen content being transmitted and the available network bandwidth. The update is only driven by the client. This gives the protocol an adaptive quality, the slower the client and the network, the slower the rate of updates.