Transducer-Based Algorithmic Verification of Retransmission Protocols over Noisy Channels

Abstract

Abstract. Unreliable communication channels are a practical reality. They add to the complexity of protocol design and verification. In this paper, we consider noisy channels which can corrupt messages. We present an approach to model and verify protocols which combine error detection and error control to provide reliable communication over noisy channels. We call these protocols retransmission protocols as they achieve reliable communication through repeated retransmissions of messages. These protocols typically use cyclic redundancy checks and sliding window protocols for error detection and control respectively. We propose models of these protocols as regular transducers operating on bit strings. Streaming string transducers provide a natural way of modeling these protocols and formalizing correctness requirements. The verification problem is posed as functional equivalence between the protocol transducer and the specification transducer. Functional equivalence checking is decidable for this class of transducers and this makes the transducer models amenable to algorithmic verification. We present case studies based on TinyOS serial communication and the HDLC retransmission protocol.

Non-deterministic transducer models of retransmission protocols over noisy channels

“…In a recent work, Thakkar et al [15] present an approach of transducer based modeling of retransmission protocols over noisy channels. They show that the usual approach of abstracting message contents by symbolic constants (e.g.…”

“…a sequence of message corruptions inducing the receiver to deliver an incorrect sequence of messages to its client (see [15], Section 2). Thus, we need an expressive framework to precisely model retransmission protocols.…”

“…Thakkar et al [15] have recently presented an algorithmic verification technique for deterministic streaming string transducer (DSST) models of such protocols. The verification problem is posed as equivalence checking between the specification and protocol DSSTs.…”

On the Minimization and Equivalence Checking of Sequential Reactive Systems

“…The more succinct is the presentation of these transducers, the more efficient are regular model checking algorithms. The authors of [17] proposed models of communication protocols as regular transducers operating on bit strings and set up the verification problem as equivalence checking between the protocol transducer and the specification transducer. These considerations show that algorithms for building compositions of transducers, checking equivalence, reducing their state space considerably enhance the effectiveness of designing, verification and maintenance of software routines.…”

On the Minimization of Finite State Trans- ducers over Semigroups

“…Понятно, что чем проще устроены эти преобразователи, тем эффективнее работа-ют алгоритмы верификации регулярных моделей такого рода. В статье [14] пред-ложено использовать в качестве модели коммуникационных протоколов автоматы-преобразователи, работающие над битовыми строками, и решать проблему вери-фикации протоколов как задачу проверки эквивалентности двух преобразователей, один из которых моделирует протокол, а другой описывает его спецификацию. При-веденные примеры свидетельствуют о том, что алгоритмы проверки эквивалентно-сти и уменьшения размеров автоматов-преобразователей востребованы для решения задач проектирования, верификации и оптимизации некоторых программ.…”