An Inproved Method for Constructing Multiphase Communications Protocols

Research has shown that many communications protocols exhibit multiple phases of behavior, performing a distinct function in each phase. A systematic method has been proposed by Chow, Gouda, and Lam for building multiphase protocols. By connecting several simpler protocols modeling the specific phases in a disciplined way, the newly constructed multiphase protocol enjoys the same correctness properties as the individual phases. The inherent modularity of the resultant protocol makes it easier to understand and analyze. However, the applicability of the existing method is subject to two rather stringent restrictions: the inability to handle message corruption or loss during phase transitions, and a rigid requirement on the selection of the points that connect different phases. This paper describes an improved method that either relaxes or eliminates the above restrictions. The construction of the Normal Response Mode of HDLC (Highlevel Data-Link Control) is presented to illustrate the use of this new method.