Network protocol: A structured approach

Abstract

Network protocols are modeled by processes exchanging messages through communication channels. For finite state protocols, each process participating in the protocol can be represented by a finite state graph. In this paper, we introduce a structuring principle for finite state protocols in the form of subgraphs. By structured protocols, we mean the following. The protocol graph can be partitioned into or be constructed from subgraphs each having a unique entry node and zero or more exit nodes. The exit nodes of one subgraph can be connected only to the entry nodes of other subgraphs. Moreover, a process in one subgraph can exchange events with another process in its corresponding subgraph only, i.e. there are no 'cross interaction' between subgraphs. Finally, from the standpoint of protocol design or synthesis, we require that when one process makes a transition into another subgraph, the other process will follow suit. Protocols that satisfy the above properties are structured in the sense that their logical correctness can be inferred from the logical correctness of individual protocol subgraphs.