33219681
Linear Broadcast Routing
14479349
Understanding and verifying distributed algorithms using stratified decomposition
Designers of autonomous distributed algorithms ( i.e., algorithms whose complete input is available before the start of execution) customarily refer to temporal ordering in describing the behavior of their algorithms-statements like “after A, task B is performed.” In the absence of an explicit termination detection for A built into the algorithm such a statement should be puzzling. However, the available proof methodologies do not seem to hinge on such statements. This paper provides firm theoretical ground for such as*Supported by NSF Presidential Young Investigators Award under grant DCR84-51396 and matching funds from IBM Faculty Development Award under grant D840622. Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/ or specific permission.
12857629
Simple Proof Techniques for Property Preservation via Simulation
Let s1 and s2 be two reactive systems related by simulation. For what kind of properties φ can one infer s1 ≒ φ (s1 satisfies φ) from s2 ≒ φ, or vice versa? This problem has been treated in the literature for various logics in which to express φ. In this paper we make two simple observations by which such results can be proved very easily: 
1. 
(1) proofs of property preservation can be made compositional, and 
 
2. 
(2) infinitary logics are very expressive. Neither observation is new, but together they yield modular proofs of nontrivial results.
37293977
Mechanical Verification of Distributed Algorithms in Higher-Order Logic
The only way to verify the correctness of a distributed algorithm with a high degree of confidence is to construct a correctness proof that is so formal and rigorous as to be checkable by a machine. The chief aim of this paper is to show, via a simple but typical example, how such proofs can be constructed and checked using HOL—a mechanical theorem-proving system for higher-order logic. The secondary aim is to demonstrate a method for reasoning about distributed algorithms based on the notions of events and causality. The goal is to perform as much reasoning as possible in the events-and-causality view and then translate the results back to the processors-and-messages view, since the former is more abstract and easier to reason about than the latter. The example we use to illustrate our ideas is the verification of a simple distributed summation algorithm for trees. A companion paper [6] describes the formal graph theory needed for this task.
7608405
Dynamic routing of restorable QoS connections in MPLS networks
In this paper we consider dynamic routing of restorable quality of service (QoS) connections in multi-protocol label switched (MPLS) networks under a single link failure model. To route a restorable QoS connection, two link disjoint label switched paths from the ingress to the egress node need to be computed such that both paths comply with the QoS constraints. When looking at QoS constraints like bandwidth guarantee and end-to-end delay bound, the current approach described in the literature converts the end-to-end delay bound into an effective bandwidth in a pre-processing step before computing two link disjoint bandwidth guaranteed paths. We argue that the current approach results in poor network performance and suggest a new approach that exploits the dependency between the end-to-end delay, chosen path and provisioned bandwidth. Thus, the two link disjoint paths are computed dynamically with their respective bandwidths so that they meet both the bandwidth guarantee and the end-to-end delay bound. In this paper, we present a new generic algorithm and two new linear programming formulations that implement the new approach. The two linear programming formulations are not intended to be used in a production environment due to their extensive running times, up to 2.5 minutes on average per request, but rather to benchmark approximation algorithms that in turn can be used in production. Furthermore our experiments show that the network performance improvement when exploiting the dependency between end-to-end delay, chosen path and provisioned bandwidth is substantial
16192278
A distributed location service for reducing query failures in geographic ad hoc routing
Location service support is required for mobile nodes using geographic ad hoc routing. The mobile nodes need location information of destinations for sending data packets. Due to mobility or node failures, queries to the location servers may not always succeed. This paper presents a distributed location service (DLS) that employs dual servers to maintain position information of mobile nodes and to achieve efficient performance. With the scheme, the number of failed queries, including no response and erroneous results, can be reduced. DLS has been implemented and evaluated using the ns2 simulator. The experimental results show that DLS not only improved service availability but also location query latency.
9337287
Detection and Recovery for Disconnection Failures in a Web-based Medical Teleconsultation System
With the progress of advanced technology, people anticipate better quality in the medical health care service. Due to more robust requirements in medical environments, higher availability and reliability are expected. This paper describes a recovery scheme for disconnection failures in a Web-based medical teleconsultation system. With the support, the disconnected clients can re-enter the system to resume the unfinished discussion using the synchronization mechanisms. The experiments have shown that the mechanism performed successfully. The lazy synchronization further reduced the required time that the clients had to wait for joining the consultation after network disconnections
14928068
Traffic engineering for MPLS-based virtual private networks
This paper considers the traffic engineering of MPLS-based Virtual Private Networks (VPNs) with multiple classes of service in an offline and centralised setting. We focus on two main issues. Firstly, we point out that the one label switched path (LSP) per ingress-egress pair constraint can be relaxed for the case of MPLS-based VPNs due to the ease in classifying flows on a per-VPN basis. This allows us to use LSP with finer granularity and thus better load balancing. Secondly, we point out that the single objective traffic engineering formulations proposed in literature address only one particular aspect of the traffic engineering problem. In this paper, we propose a multiobjective traffic engineering problem which takes resource usage, link utilisation and number of LSPs into account. The proposed optimisation problem is NP-complete and involves a large number of variables. We propose an heuristic to solve this problem.
7646347
Provisioning overlay distribution networks
Future entertainment services are expected to be increasingly interactive, on demand and personalized. This paper aims to address the challenge of provisioning network and server resources to support the distribution of these services over the Internet. We propose the Overlay Distribution Network (ODN) as a cost-effective means to deliver these services. Because ODNs are created over shared network and server infrastructure, the provisioning problem becomes significantly complex. The paper formulates this problem as a joint resource provisioning and content replication optimization. The resulting formulation is proved to be NP-complete. We solved this problem with an efficient Lagrangian heuristic. Further, content clustering is employed to improve the heuristic run time. Initial results show that this is efficient. In some cases, clustering allows solutions with very similar quality to be achieved at a 20 times reduction in complexity.