Colin H. West

An improved protocol validation technique

Abstract It is shown that communication between asynchronous processes can be expressed as sequences of nondecomposable, basic interaction which in the general case involve multiple message exchanges. Consideration of the form of these interactions leads to an understanding of the limitations of protocol-validation techniques and improves their efficiency.

An Automated Technique of Communications Protocol Validation

An interaction between two communicating processes can be defined in terms of a protocol or set of rules governing the exchange of messages between them. For any given protocol, it is a significant problem to determine whether or not errors can occur when the processes interact. In this paper, we describe an implementation of a recent theory of Zafiropulo, which defines protocols in terms of the interaction between two directed graphs, and uses set theory and predicate logic to determine all error conditions that can arise. The overall structure of the theory is used, but the determination of the error conditions is based on a graphical representation of the interaction, and particular emphasis is placed on the state of the channel between the two processes. The technique is currently limited to the validation of two-process protocols in which the processes return to an initial state after a finite number Of interaction steps. The implementation demonstrates that a completely automated procedure can be defined which finds a significant class of errors in communications protocols.

Protocol validation in complex systems

Protocol validation and verification techniques have been applied successfully for a number of years to a wide range of protocols. The increasing complexity of our communications systems requires us to examine existing techniques and make a realistic assessment of which techniques will be applicable to the complex systems of the future. We believe that validation techniques based on an exhaustive reachability analysis will not be effective. Sampling techniques, such as executing a random walk through the reachable state space, are effective in complex systems, since most protocol errors occur in many different states of the system. More than 10 years have elapsed since the first automated validation techniques were first applied to communications protocols [1,2]. In the meantime, considerable advances have been made in validation technology, but more significantly, the scale and nature of the validation problem have changed. The communications systems that we need to validate today are significantly more complex than those of ten years ago. Our methods must evolve in order to address the current challenge. This paper is concerned primarily with the nature of the validation process, and the results that we might reasonably expect to achieve when validating protocols in complex communications systems.

Automated protocol validation: One chain of development

Abstract The progress of one research effort in computer-automated protocol validation is summarized in this paper. It brings together in one place the results of a number of studies, some published and some to be published but all widely scattered in the literature. Described are a formal representation, the “duologue”, “phase-diagram”, and “state-pertubation” methods. These are discussed on the basis of a common example. Sample results from the validation of the CCITT X.21 interface are explained as an indication of what these techniques can achieve.

Protocol validation: principles and applications

Abstract We describe two techniques that have been developed for automated protocol validation, reachability analysis and random walk validation. A number of case studies are presented in order to demonstrate how the techniques can be applied to protocols of varying complexity. The effectiveness of automated protocol validation is discussed in terms of a simple model that shows why analysis of a restricted sample of the states in the reachable state space is sufficient to identify most errors when the latter are limited complexity.

Protocol Analysis and Synthesis using a State Transition Model

The growing trends both to increase the sophistication of functions implemented in information-handling systems and to distribute these functions in different processes has resulted in an enormous growth in complexity. This complexity is particularly acute in the interactions or protocols which specify how these processes are synchronized and communicate with one another. However, formal methods are gradually being introduced to describe these interactions; see chapters 20, 21, 23, and 25 as well as [l]–[5].

A validation of the OSI session layer protocol

Abstract The session layer of the ISO Open-System-Interconnection (OSI) Protocol has been validated using an automated state-exploration technique. The validation methodology is described, together with the particular way it has been applied to the session layer. A number of the protocol errors found is presented.

Proxy PNNI augmented routing (proxy PAR)

ATM networks often carry other popular communication protocols such as TCP/IP. LAN emulation techniques, with LANE and MPOA being the most prominent ones, make it possible to support existing applications, but do not take advantage of many ATM capabilities. Furthermore, such server-based solutions often suffer from single point of failure problems. PNNI Augmented Routing (PAR), based on Private Network–Network Interface (PNNI), enables ATM and TCP/IP to be better integrated than in an emulation environment. In addition to that, Proxy PAR has been introduced as a minimal version of PAR that gives ATM-attached devices the ability to interact with PNNI devices without the complexity associated with a full PAR implementation. Proxy PAR has been conceived as a client/server interaction in which the client side is much simpler than the server side, permitting fast implementation and deployment in existing IPv4 devices. The main purpose of Proxy PAR is to allow non-ATM devices to use the flooding mechanisms provided by PNNI for registration and automatic discovery of services offered. Proxy PAR capable servers support filtering based on Virtual Private Network (VPN) IDs, IP protocols and address prefixes. This enables, for example, routers in a certain VPN running OSPF to find their neighboring routers without the manual configuration implied by other technologies such as Frame Relay.

Some notes on the history of protocol engineering

During the 1970s and 1980s, the first computer communication networks were designed and implemented in the research and commercial sectors. Many of the protocols developed during that time are still in use today. This paper starts by giving an overview of these developments. Then it concentrates on the development of protocol engineering, that is, the methods for the specification of communication protocols and services, the verification of protocols and their implementation and testing. After personal views of the developments in the 1970s, the basic concepts developed at that time are explained. The standardization of Formal Description Techniques in the 1980s is discussed in the following section, as well as the standardization of conformance testing. The purpose of the paper is to show the long way we have come and to suggest that many of the basic concepts have not changed too much during these years, although more detailed aspects have evolved and given rise to new technological developments.

Experiences with a random test driver

We describe our experience with a methodology for testing implementations of communications protocols that uses autonomous test drivers to exercise the protocol service interface. The test drivers only generate random event sequences that the service interface specifies should be accepted by a correct implementation. Event rejection therefore indicates a discrepancy between the service specification and the implementation under test. The methodology has proved to be a powerful and cost-effective complement to other testing techniques.