Compressing the X protocol

John Danskin

Department of Computer Science
Dartmouth

Abstract

The most common instance of networked graphics is the X terminal. X and other graphics protocols allow the application program to be independent of its display. This separation comes with a cost: bits must be shipped across a network which may have limited capacity. Wireless networks, telephone connections, and cellular telephone connections have especially limited capacity. HBX is a compression protocol for increasing effective network capacity for X. HBX uses predictive models, arithmetic coding, and syntactic and semantic knowledge about the X protocol to achieve compression ratios averaging about 7.6:1 across a representative trace suite (three times the compression performance of NCD's Xremote protocol). I will discuss network parameters, alternatives in graphics protocol design, the performance of Xremote (NCD's compressed X protocol), compression techniques, the HBX implementation and results, and outline some possible directions for future work.