The Two-Dimensional Window Protocol

Abstract

We develop a generalization of the window protocol where data messages are sent in independent streams. Each stream has its own window, but the window sizes of different streams can be changed at runtime under the restriction that their sum remains constant. This restriction is needed to establish an upper bound on the required resources for the protocol. Our development of this protocol is “gentle” as it is divided into three “easy” steps. First, a regular window protocol is presented and formally verified. Second, this window protocol is extended to allow multiple data streams with fixed window sizes. The extended protocol is verified by extending the verification of the window protocol in a straightforward manner. Third, the multiple stream protocol is modified to allow the window sizes of different streams to change at runtime. The modification is slight and verification of the resulting protocol is derived from the verification of the multiple stream protocol.