Sliding Window Protocol Research Articles

Sliding window protocol with selective-repeat ARQ: performance modeling and analysis

A sliding window mechanism is well known to be a convenient way to integrate cumulative acknowledgement and flow control functions in a simple manner. Hence, widely used reliable data-transfer protocols such as TCP-SACK and RLC utilize this sliding window mechanism in conjunction with a selective-repeat ARQ (automatic repeat request) function, namely, the selective-repeat sliding window protocol (SR-SWP). We demonstrate that SR-SWP yields a throughput restraint effect (TORE) in particular situations when packet losses occur. We propose an analytical performance model to represent the TORE in the case of heavy traffic. Using this model, we derive explicit forms of goodput and mean resequencing delay, which are fundamental qualities of service parameters. From numerical results, we demonstrate that the impact of TORE on the performance is not negligible for high packet-loss probabilities. Furthermore, we show that the SR-SWP model exhibits the lower goodput and the smaller mean resequencing delay than those obtained from the traditional SR-ARQ protocol model.

Verification of a sliding window protocol in μ CRL and PVS

Abstract We prove the correctness of a sliding window protocol with an arbitrary finite window size n and sequence numbers modulo 2 n . The correctness consists of showing that the sliding window protocol is branching bisimilar to a queue of capacity 2 n . The proof is given entirely on the basis of an axiomatic theory, and has been checked in the theorem prover PVS.

Sliding Window Protocol for Secure Group Communication in Ad-Hoc Networks

Sliding Window Protocol for Secure Group Communication in Ad-Hoc Networks

Generalization of the basic sliding window protocol

A new protocol called generalized sliding window protocol is described and formally specified using the Specification and Description Language (SDL). The protocol generality was achieved by appropriately combining the classical go-back-n and selective-repeat protocols that both have traditionally been referred to as sliding window protocols. The proposed protocol is valid for any combination of send and receive window widths. The stop-and-wait, go-back-n and selective-repeat protocols are shown to be its special cases. Simulations show that the protocol efficiency initially increases with the increase of the receive window width, but can saturate or even reach its maximum value at a receive window width that is less than the send window width. This offers more freedom to choose a suitable compromise between buffer lengths and protocol efficiency, and an optimal efficiency may be achieved using less resources than with the selective-repeat protocol. The described protocol can serve as a starting point for the further development of new protocols, but can also be used as a simple, unified and theoretically sound protocol to be taught to telecommunications students. Copyright © 2004 John Wiley & Sons, Ltd.

SeSFJava Harness: Service and Assertion Checking for Protocol Implementations

Many formal specification languages and associated tools have been developed for network protocols. Ultimately, formal language specifications have to be compiled into a conventional programming language and this involves manual intervention (even with automated tools). This manual work is often error prone because the programmer is not familiar with the formal language. So our goal is to verify and test the ultimate implementation of a network protocol, rather than an abstract representation of it. We present a framework, called services and systems framework (SeSF), in which implementations and services are defined by programs in conventional languages, and mechanically tested against each other. SeSF is a markup language that can be integrated with any conventional language. We integrate SeSF into Java, resulting in what we call SeSFJava. We present a service-and-assertion checking harness for SeSFJava, called SeSFJava harness, in which distributed SeSFJava programs can be executed, and the execution checked against services and any other correctness assertions. The harness can test the final implementation of a concurrent system. We present an application to a data transfer service and sliding window protocol implementation. SeSFJava and the harness has been used in networking courses to specify and test transmission control protocol-like transport protocols and service.

Fighting livelock in the GNU i-protocol: a case study in explicit-state model checking

The i-protocol, an optimized sliding-window protocol for GNU uucp, first came to our attention in 1995 when we used the Concurrency Factory’s local model checker to detect, locate, and correct a non-trivial livelock in version 1.04 of the protocol. Since then, we have conducted a systematic case study on the protocol using four verification tools, viz. Cospan, Murϕ, Spin, and XMC, each of which supports some form of explicit-state model checking. Our results show that although the i-protocol is inherently complex – the size of its state space grows exponentially in the window size and it deploys several sophisticated optimizations aimed at minimizing control-message and retransmission overhead – it is nonetheless amenable to a number of general-purpose abstraction techniques whose application can significantly reduce the size of the protocol’s state space.

Efficient parallel simulation of a sliding window protocol

Two parallel algorithms for simulating a sliding window communication protocol are described. The first exploits the parallel generation of interarrival, service and transfer times, whilst the second is based on parallel prefix computations. Both algorithms allow the processors to work largely asynchronously with each other. The efficiency of the two approaches is evaluated experimentally, using an implementation on a cluster of 12 processors connected by fast Ethernet.

Generalised sliding window protocol

A new retransmission strategy of the basic sliding window protocol is proposed. The stop-and-wait, go-back-n and selective-repeat protocols are special cases of this generalised protocol. The protocol is correct for any combination of send and receive window widths. The protocol efficiency increases with the receive window width.

A framework for modeling transfer protocols

The notion of specification frameworks transposes the framework approach from software development to the level of formal modeling and analysis. A specification framework is devoted to a special application domain. It supplies re-usable specification modules and guides the construction of specifications. Moreover, it provides theorems to be used as building blocks of verifications. By means of a suitable framework, specification and verification tasks can be reduced to the selection, parametrization and combination of framework elements resulting in a substantial support which opens formal analysis even for real-sized problems. The transfer protocol framework addressed here is devoted to the design of data transfer protocols. Specifications of used and provided communication services as well as protocol specifications can be composed from its specification modules. The theorems correspond to the relations between protocol mechanism combinations and those properties of the provided service which are implemented by them. This article centers on the application of this framework which is discussed with the help of the specification of a sliding window protocol. Moreover the structure of its verification is described. The specification and verification technique applied is based on L. Lamport's temporal logic of actions (TLA). We use the variant cTLA which particularly supports the modeling of process systems.

On measuring the complexity of an estelle specification

Software metrics are useful quantitative indicators to assess and predict software quality attributes; a commonly measured attribute is software complexity. The main drawbacks of these metrics are: they can only be calculated after a major development effort has been committed to producing the source codes; they cannot provide early feedback during the specification phase; and subsequently it is expensive to make changes to the system, if so indicated by the metrics. Formal Description Techniques (FDTs) enable formal specification to be systematically analyzed. They should also make it possible to assess software quality attributes like maintainability and reliability, and to predict the development or maintenance cost/effort early in the specification phase of the formal protocol development life cycle. To date, little work has been devoted to this area. In this paper, we describe how the complexity of an Estelle specification can be measured. The Sliding Window Protocol specified in Estelle is used as an example to illustrate our approach to measuring the complexity of an Estelle specification. The Management Decision Support System (MDSS), which integrates software measurement into the formal protocol development, is also described in this paper.

On measuring the complexity of an estelle specification

Software metrics are useful quantitative indicators to assess and predict software quality attributes; a commonly measured attribute is software complexity. The main drawbacks of these metrics are: they can only be calculated after a major development effort has been committed to producing the source codes; they cannot provide early feedback during the specification phase; and subsequently it is expensive to make changes to the system, if so indicated by the metrics. Formal Description Techniques (FDTs) enable formal specification to be systematically analyzed. They should also make it possible to assess software quality attributes like maintainability and reliability, and to predict the development or maintenance cost/effort early in the specification phase of the formal protocol development life cycle. To date, little work has been devoted to this area. In this paper, we describe how the complexity of an Estelle specification can be measured. The Sliding Window Protocol specified in Estelle is used as an example to illustrate our approach to measuring the complexity of an Estelle specification. The Management Decision Support System (MDSS), which integrates software measurement into the formal protocol development, is also described in this paper.

Self-stabilizing sliding window ARQ protocols

It is shown that implementing a practical self-stabilizing sliding window protocol requires a bound on the maximum delay or maximum memory of the communication channel involved. This motivates using communication channel models that incorporate a delay or memory bound. For such models, two new ARQ protocols are presented that self-stabilize by using 1 bit of overhead in each transmitted message. The protocols operate like selective repeat ARQ, except that when a fault places them in an incorrect (unsafe) state, the additional bit in the protocol messages allows automatic recovery. Following a transient fault, the bounded delay protocol stabilizes within four round-trip times. The bounded memory protocol stabilizes after sending at most 2(K+n) messages, where K the is maximum number of messages that can be stored in one direction on the channel, and n is the window size of the sender.

Alternative specification and verification of a periodic state exchange protocol

The formal analysis of a data-transfer protocol based on the novel idea of periodic state exchange has been presented by Gouda et al. (see IEEE Trans. Commun., vol.43, no.9, p.2475-84, 1995). In certain environments, such as the Internet, the requirements for the correctness of the protocol may impose impractical constraints. We present an alternative specification of the periodic state-exchange protocol based on the discovery that the protocol can be treated as a special sliding-window protocol. Although our protocol behaves better in an Internet-like environment it has other shortcomings with respect to the original. The comparison of the alternatives reveals the trade-offs in their design.

Testing abstract distributed programs and their implementations: A constraint-based approach

An abstract program is a formal specification that models the valid behavior of a concurrent program without describing particular implementation mechanisms that achieve this behavior. Valid behavior can be modeled as the possible sequences of events that may be observed of a conforming concrete implementation of the abstract program. In this article, we address the problem of how to select event sequences from an abstract program to test its concrete implementation. Sequencing constraints make explicit certain types of required properties that are expressed only implicitly by the abstract program itself. The sequencing constraints derived from an abstract program can be used to guide the selection of event sequences during testing: sequences are selected to check the implementation for conformance to the required properties. We describe a constraint notation called CSPE and formally define CSPE constraints in the propositional modal μ-calculus. CSPE constraints can be automatically derived from abstract CCS and Lotos programs, and test sequences can be generated to cover the constraints. We describe a test sequence generation tool that can be used to partially automate this process. The test sequence generator inputs an abstract program and a list of constraints, and outputs a list of test sequences. The test sequence generator was used in an experiment to measure the effectiveness of the test sequences. We created mutations of a nontrivial concurrent Ada program in order to determine the mutation adequacy of a set of test sequences generated from an abstract program. The abstract program was a specification of the Sliding Window Protocol. The results of the experiment are reported.

Verifying Programs with Unreliable Channels

We consider the verification of a particular class of infinite-state systems, namely systems consisting of finite-state processes that communicate via unbounded lossy FIFO channels. This class is able to model, e.g., link protocols such as the Alternating Bit Protocol and HDLC. For this class of systems, we show that several interesting verification problems are decidable by giving algorithms for verifying (1) thereachability problem—is a finite set of global states reachable from some other global state of the system ? (2)safety properties over tracesformulated as regular sets of allowed finite traces, and (3)eventuality properties—do all computations of a system eventually reach a given set of states? We have used the algorithms to verify some idealized sliding-window protocols with reasonable time and space resources. Our results should be contrasted with the well-known fact that these problems are undecidable for systems with unboundedperfectFIFO channels.

The sliding-window protocol revisited

Abstract We give a correctness proof of the sliding-window protocol. Both safety and liveness properties are addressed. We show how faulty channels can be represented as nondeterministic programs. The correctness proof is given as a sequence of correctness-preserving transformations of a sequential program that satisfies the original specification, with the exception that it does not have any faulty channels. We work as long as possible with a sequential program, although the transformation steps are guided by the aim of going to a distributed program. The final transformation steps consist in distributing the actions of the sequential program over a number of processes.

A protocol test system for the study of sliding window protocols on networked UNIX computers

A software-based system for modeling transport layer protocols and observing their behavior and performance in an actual local area network setting is introduced. The simple interface definition provides for rapid prototyping of the flow control, error recovery and connection management features of transport layer protocols. The ability to introduce errors into the communications stream allows for testing in a variety of situations which are troublesome for communications protocols, such as long delays in delivery and acknowledgment, packet loss, and high noise rates. This protocol test system (PTS) is intended as a tool which can provide a practical environment in which students and engineers can develop and study communications protocols,. >

Corrigendum to A Correctness Proof of a One-bit Sliding Window Protocol in CRL

Corrigendum to A Correctness Proof of a One-bit Sliding Window Protocol in CRL

A Correctness Proof of a One-bit Sliding Window Protocol in CRL

We model a one-bit sliding window protocol and prove that its external behaviour is a bi-directional buffer of capacity 2. The proof is given in µCRL, which is a process algebra extended with data. Due to the abundant parallelism in this protocol, the behaviour is quite complicated. The complexity has been mastered by explicitly identifying invariants and foci of cones in the protocol. Both concepts seem promising as tools for the verification of larger and more complex protocols.

Nested sliding window protocols with packet fragmentation

A single-hop OSI structured network with multiple layers of sliding window flow control and packet fragmentation between layers is analyzed. An approximation algorithm is presented to hierarchically reduce the network to a single queue whose performance characteristics represent the original network. Network transmission characteristics are restricted to Erlang distributions. Validation against exact and simulation results showed that the approximation algorithm has a satisfactory error level. >