Results 1  10
of
39
Gradient Clock Synchronization
, 2004
"... We introduce the distributed gradient clock synchronization problem. As in traditional distributed clock synchronization, we consider a network of nodes equipped with hardware clocks with bounded drift. Nodes compute logical clock values based on their hardware clocks and message exchanges, and the ..."
Abstract

Cited by 40 (1 self)
 Add to MetaCart
(Show Context)
We introduce the distributed gradient clock synchronization problem. As in traditional distributed clock synchronization, we consider a network of nodes equipped with hardware clocks with bounded drift. Nodes compute logical clock values based on their hardware clocks and message exchanges, and the goal is to synchronize the nodes’logical clocks as closely as possible, while satisfying certain validity conditions. The new feature of gradient clock synchronization (GCS for short) is to require that the skew between any two nodes’logical clocks be bounded by a nondecreasing function of the uncertainty in message delay (call this the distance) between the two nodes. That is, we require nearby nodes to be closely synchronized, and allow faraway nodes to be more loosely synchronized. We contrast GCS with traditional clock synchronization, and discuss several practical motivations for GCS, mostly arising in sensor and ad hoc networks. Our main result is that the worst case clock skew between two nodes at distance d from each other is log D Ω(d + log log D), where D is the diameter1 of the network. This means that clock synchronization is not a local property, in the sense that the clock skew between two nodes depends not only on the distance between the nodes, but also on the size of the network. Our lower bound implies, for example, that the TDMA protocol with a fixed slot granularity will fail as the network grows, even if the maximum degree of each node stays constant.
On the language inclusion problem for timed automata: Closing a decidability gap
 in Proc. LICS’04. IEEE
"... We consider the language inclusion problem for timed automata: given two timed automata A and B, are all the timed traces accepted by B also accepted by A? While this problem is known to be undecidable, we show here that it becomes decidable if A is restricted to having at most one clock. This is so ..."
Abstract

Cited by 35 (5 self)
 Add to MetaCart
(Show Context)
We consider the language inclusion problem for timed automata: given two timed automata A and B, are all the timed traces accepted by B also accepted by A? While this problem is known to be undecidable, we show here that it becomes decidable if A is restricted to having at most one clock. This is somewhat surprising, since it is wellknown that there exist timed automata with a single clock that cannot be complemented. The crux of our proof consists in reducing the language inclusion problem to a reachability question on an infinite graph; we then construct a suitable wellquasiorder on the nodes of this graph, which ensures the termination of our search algorithm. We also show that the language inclusion problem is decidable if the only constant appearing among the clock constraints of A is zero. Moreover, these two cases are essentially the only decidable instances of language inclusion, in terms of restricting the various resources of timed automata. 1.
A.: Timed I/O Automata: A Complete Specification Theory for Realtime Systems
 In: HSCC 2010
, 2010
"... A specification theory combines notions of specifications and implementations with a satisfaction relation, a refinement relation and a set of operators supporting stepwise design. We develop a complete specification framework for realtime systems using Timed I/O Automata as the specification form ..."
Abstract

Cited by 34 (15 self)
 Add to MetaCart
(Show Context)
A specification theory combines notions of specifications and implementations with a satisfaction relation, a refinement relation and a set of operators supporting stepwise design. We develop a complete specification framework for realtime systems using Timed I/O Automata as the specification formalism, with the semantics expressed in terms of Timed I/O Transition Systems. We provide constructs for refinement, consistency checking, logical and structural composition, and quotient of specifications – all indispensable ingredients of a compositional design methodology. The theory is implemented on top of an engine for timed games, Uppaaltiga, and illustrated with a small case study.
Modeling and Verification of a FaultTolerant Realtime Startup Protocol using Calendar Automata
, 2004
"... We discuss the modeling and verification of realtime systems using the SAL model checker. A new modeling framework based on event calendars enables dense timed systems to be described without relying on continuously varying clocks. We present verification techniques that rely on induction and ab ..."
Abstract

Cited by 32 (2 self)
 Add to MetaCart
(Show Context)
We discuss the modeling and verification of realtime systems using the SAL model checker. A new modeling framework based on event calendars enables dense timed systems to be described without relying on continuously varying clocks. We present verification techniques that rely on induction and abstraction, and show how these techniques are e#ciently supported by the SAL symbolic modelchecking tools. The modeling and verification method is applied to the faulttolerant realtime startup protocol used in the Timed Triggered Architecture.
Clock Synchronization for Wireless Networks
 In Proc. 8th International Conference on Principles of Distributed Systems (OPODIS
, 2004
"... Abstract. Time synchronization is a fundamental service in many wireless applications. While the synchronization problem is wellstudied in traditional wired networks, physical constraints of the wireless medium impose a unique set of challenges. We present a novel time synchronization algorithm whi ..."
Abstract

Cited by 16 (3 self)
 Add to MetaCart
(Show Context)
Abstract. Time synchronization is a fundamental service in many wireless applications. While the synchronization problem is wellstudied in traditional wired networks, physical constraints of the wireless medium impose a unique set of challenges. We present a novel time synchronization algorithm which is highly energy efficient and failure/recoverytolerant. Our algorithm allows nodes to synchronize to sources of real time such as GPS when such signals are available, but continues to synchronize nodes to each other, even in the absence of GPS. In addition, the algorithm satisfies a relaxed gradient property, in which the degree of synchronization between nodes varies as a linear function of their distance. Thus, nearby nodes are highly synchronized, which is desirable in many wireless applications. 1
Translating Timed I/O Automata Specifications for Theorem Proving in PVS
, 2006
"... The timed input/output automaton modeling framework is a mathematical framework for specification and analysis of systems that involve discrete and continuous evolution. In order to employ an interactive theorem prover in deducing properties of a timed input/output automaton, its statetransition bas ..."
Abstract

Cited by 15 (9 self)
 Add to MetaCart
The timed input/output automaton modeling framework is a mathematical framework for specification and analysis of systems that involve discrete and continuous evolution. In order to employ an interactive theorem prover in deducing properties of a timed input/output automaton, its statetransition based description has to be translated to the language of the theorem prover. This thesis describes a tool for translating from TIOA, the formal language for describing timed input/output automata, to the language of the Prototype Verification System (PVS)a specification system with an integrated interactive theorem prover. We describe the translation scheme, discuss the design decisions, and briefly present case studies to illustrate the application of the translator in the verification process.
PVS Strategies for Proving Abstraction Properties of Automata
 STRATEGIES 2004 PRELIMINARY VERSION
, 2004
"... ..."
(Show Context)
TIOA User Guide and Reference Manual
, 2005
"... TIOA is a simple formal language for modeling distributed systems with timing as collections of interacting state machines, called timed input/output automata. The TIOA Toolkit supports a range of validation methods, including simulation and machinechecked proofs. This user guide and reference manu ..."
Abstract

Cited by 11 (1 self)
 Add to MetaCart
TIOA is a simple formal language for modeling distributed systems with timing as collections of interacting state machines, called timed input/output automata. The TIOA Toolkit supports a range of validation methods, including simulation and machinechecked proofs. This user guide and reference manual includes a tutorial on the use of timed input/output automata and the TIOA language to model timed systems. It also includes a complete definition of the TIOA language.
Specifying and proving timing properties with TIOA tools
 In Work in progress session of the 25th IEEE International RealTime Systems Symposium (RTSSWIP
, 2004
"... ..."
(Show Context)