Robust chat for airborne command and control

Abstract

We present the design, implementation, and evaluation of a prototype robust textual chat application to be utilized in dynamic distributed environments such as the Multi-Sensor Command and Control Constellation (MC2C). The MC2C environment consists of a set of airborne and ground sites, each of which contains a cluster of clients. Intra-site communication is reliable and exhibits high performance, whereas the performance and reliability of inter-site communication is variable and unpredictable. The two primary goals of the chat application are to deliver messages to clients with low latency and a globally consistent ordering. Since these goals conflict, our protocols strike a balance by satisfying a new property that we call the Intermittent Global Order (IGO) property. A protocol satisfying the IGO property guarantees global order while network connectivity permits, and sacrifices global order for bounded message delivery latencies while maintaining an intuitive and well-defined ordering on the message delivery when critical network connections are lost. We implemented our protocols on a hierarchical system architecture that places a server at every MC2C site. We developed a test-bed that simulates four MC2C sites in order to test the prototype. Testing revealed that the various IGO protocols implemented in the prototype all achieve the goals of robust and efficient collaborative communication even in the face of frequent link outages, but differ in how each balances global order and latency.