We design a reset subsystem that can be embedded in an arbitrary distributed system in order to allow the system processes to reset the system when necessary. Our design is layered, and comprises three main components: a leader election, a spanning tree construction, and a diffusing computation. Each of these components is self-stabilizing in the following sense. If the coordination between the up processes in the system is ever lost (due to failures or repairs of processes and channels) then each component eventually reaches a state where coordination is regained. This capability makes our reset subsystem very robust: it can tolerate fail-stop failures and repairs of processes and channels even when a reset is in progress. Categories and Subject Descriptors: C.2.4 [Computer Communication Systems]: Distributed Systems--distributed applications, network operating systems ; D.1.3 [Programming Techniques]: Concurrent Programming ; D.4.5 [Operating Systems]: Reliability--verification, fa...

Hop-by-hop inter-domain routing protocols, such as BGP and IDRP, use independent route selection to realize domains ’ local policies. A domain chooses its routes based on path attributes present in a route. It is widely believed that these inter-domain routing protocols always converge. We show that there exist domain policies that cause BGP/IDRP to exhibit persistent oscillations. In these oscillations, each domain repeatedly chooses a sequence of routes to a destination. Complex oscillation patterns can occur even in very simple topologies. We analyze the conditions for persistent route oscillations in a simple class of interdomain topologies and policies. Using this analysis, we evaluate ways to prevent or avoid persistent oscillations in general topologies. We conclude that if a hop-by-hop inter-domain routing protocol allows unconstrained route selection at a domain, the protocol may be susceptible to route oscillations. Constraining route selection to a provably “safe ” procedure (such as shortest path) can reduce the number of realizable policies. Alternatively, a routing policy registry can help detect unsafe policies.

A new approach for structuring distributed processing systems, called functionally accurate, cooperative (FA/C), is proposed. The approach differs from conventional ones in its emphasis on handling distribution-caused uncertainty and errors as an integral part of the network problem-solving process. In this approach nodes cooperatively problem solve by exchanging partial tentative results (at various levels of abstraction) within the context of common goals. The approach is especially suited to applications in which the data necessary to achieve a solution cannot be partitioned in such a way that a node can complete a task without seeing the intermediate state of task processing at other nodes. Much of the inspiration for the FA/C approach comes from the mechanisms used in knowledge-based artificial intelligence (AI) systems for resolving uncertainty caused by noisy input data and the use of approximate knowledge. The appropriateness of the FA/C approach is explored in three application domains: distributed interpretation, distributed network traffic-light control, and distributed planning. Additionally, the relationship between the approach and the structure of management organizations is developed. Finally, a number of current research directions necessary to more fully develop the FA/C approach are outlined. These research directions include distributed search, the integration of implicit and explicit forms of control, and distributed planning and organizational self-design. I.

Abstract — Periodic checkpointing of the entire system state and rolling back to the last checkpoint when an error is detected is proposed as a basis for error recovery on a VLSI multicomputer executing non-interactive applications. Detailed algorithms for saving the checkpoints, distributing diagnostic information, and restoring a valid system state are presented. This approach places no restrictions on the actions of the application tasks, and, during normal computation, does not require the complex communication protocols that are part of most other schemes. Estimates of the overhead of the proposed scheme are presented and extensions for efficient handling of transient faults, input/output operations, and disk failures are discussed.

In a dynamic network environment under heavy traffic load, shortest-path routing algorithms, particularly those that attempt to adapt to traffic changes, frequently exhibit oscillatory behaviors and cause performance degradation. In this paper we first examine the problems from the perspective of control theory and decision making, and then analyze the behaviors of the shortest-path routing algorithms in details. 1. INTRODUCTION Shortest-path routing algorithms have been widely used in today's computer networks. In such algorithms, each node attempts to route packets to their destinations over paths of minimum distance and updates the distances periodically to adapt topological and traffic changes. There are two main classes of algorithms: distance-vector algorithm and link-state algorithm. In a distance-vector algorithm, each node maintains a routing table containing the distance of the shortest path to every destination in the network. A node only informs its immediate neighbors of...

We give a distributed algorithm to compute shortest paths in a network with changing topology. It does not suffer from the routing table looping behavior associated with the FordBellman distributed shortest path algorithm although it uses truly distributed processing. Its time and message complexities are evaluated. Pierre Humblet is with the Laboratory for Information and Decision Systems, Massachusetts Institute of Technology, Cambridge MA 02139. This research was supported in part by Codex Corporation and in part by the Army Research Office under Grant No. DAAL03-86-K-0171. 2 1) INTRODUCTION One of the oldest and best known problems in the field of distributed algorithms is to compute shortest paths between nodes in a network. This problem arises in the following context. We have a network of links and nodes (processors). Each link (I,J) is characterized by a direction dependent length LEN(I,J) that can change with time and can only be observed at node I. The nodes execute a distr...

Power-supply, a surprisingly simple and new general paradigm for the development of self-stabilizing algorithms in different models, is introduced. The paradigm is exemplified by developing simple and efficient self-stabilizing algorithms for leader election and either BFS or DFS spanning tree constructions, in strongly-connected unidirectional and bidirectional dynamic networks (synchronous and asynchronous). The different algorithms stabilize in O(n) time in both synchronous and asynchronous networks without assuming any knowledge about the network topology or size, where n is the total number of nodes. Following the leader election algorithms we present a generic self-stabilizing spanning tree and/or leader election algorithm that produces a whole spectrum of new and efficient algorithms for these problems. Two variations that produce either a rooted Depth First Search tree or a rooted Breadth First Search tree are presented. 1 Introduction A distributed system is self-s...

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In this paper, we present a new methodology for developing systematic and automatic test generation algorithms for multipoint protocols. These algorithms attempt to synthesize network topologies and sequences of events that stress the protocol’s correstness or performance. This problem can be viewed as a domain-specific search problem that suffen from the state space explosion problem. One goal of this work is to circumvent the state space explosion problem utilizing knowledge of network and fault modeling, and multipoint protocols. The two ap-proaches investigated in this study are based on forward and backward search techniques. We use an extended finite state machine (FSM) model of the protocol. The fint algorithm uses forward search to perform reduced reachability analysis. Using domain-specific information for multicast routing over LANs, the algorithm complexity is reduced from exponential to polynomial in the number of routers. This approach, however, does not fully automate topology synthesis. The second algorithm, the fault-oriented test generation, uses backward search for topology synthesis and uses backtracking to generate event sequences instead of searching forward from initial states. Using these algorithms, we have conducted studies for correctness of the multicast routing protocol PIM. I.

Two self-stabilizing topology maintenance protocols for high speed networks are presented. The protocols tolerate any number and kind of initial faults. The new protocols improve on previous protocols by their stabilization time (the amount of time following the last topology change required to notify every processor of the correct topology), by their utilization of limited switch bandwidth, and by their avoiding the use of unbounded sequence numbers. The rst protocol stabilizes in O(log d) time in the worst case, where d is the diameter of the network. This protocol imposes a high bandwidth requirement on individual network nodes. The second, which is implemented by two software layers, reduces the processing load on individual nodes and stabilizes within O(d) time in the worst case and O(1) time when changes are infrequent. An extended abstract of this paper appeared as [AC+94a].