Implementing Network Protocols as Distributed Logic Programs

Declarative networking [2, 4, 3, 1] is an application of database query-language and processing techniques to the domain of networking. Declarative networking is based on the observation that network protocols deal at their core with computing and maintaining distributed state (e.g., routes, sessions, performance statistics) according to basic information locally available at each node (e.g., neighbor tables, link measurements, local clocks) while enforcing constraints such as local routing policies. Recursive query languages studied in the deductive database literature [6] are a natural fit for expressing the relationship between base data, derived data, and the associated constraints. Simple extensions to these languages and their implementations enable the natural expression and efficient execution of network protocols. Declarative networking aims to accelerate the process of specifying, implementing, experimenting with and evolving designs for network architectures. Declarative networking can reduce program sizes of distributed protocols by orders of magnitude relative to traditional approaches. In addition to serving as a platform for rapid prototyping of network protocols, declarative networking also open up opportunities for automatic protocol optimization and hybridization, program checking and debugging. This paper presents an introduction to declarative networking using a simple routing protocol example. For more details on declarative networking related projects, refer to the NetDB@Penn website [5], and the RapidNet [7] declarative networking engine

Peer-To-Peer Backup for Personal Area Networks

FlashBack is a peer-to-peer backup algorithm designed for power-constrained devices running in a personal area network (PAN). Backups are performed transparently as local updates initiate the spread of backup data among a subset of the currently available peers. Flashback limits power usage by avoiding flooding and keeping small neighbor sets. Flashback has also been designed to utilize powered infrastructure when possible to further extend device lifetime. We propose our architecture and algorithms, and present initial experimental results that illustrate FlashBack’s performance characteristic

Maintaining Distributed Recursive Views Incrementally

This paper proposes an algorithm to compute incrementally the changes to distributed recursive database views in response to insertions and deletions of base facts. Our algorithm uses a pipelined semi-näıve (PSN) evaluation strategy introduced in declarative networking. Unlike prior work, our algorithm is formally proven to be correct for recursive query computation in the presence of message reordering in the system. Our proof proceeds in two stages. First, we show that all the operations performed by our PSN algorithm computes the same set of results as traditional centralized semi-näıve evaluation. Second, we prove that our algorithm terminates, even in the presence of cyclic derivations due to recursion

Real-Time MapReduce Scheduling

In this paper, we explore the feasibility of enabling the scheduling of mixed hard and soft real-time MapReduce applications. We first present an experimental evaluation of the popular Hadoop MapReduce middleware on the Amazon EC2 cloud. Our evaluation reveals tradeoffs between overall system throughput and execution time predictability, as well as highlights a number of factors affecting real-time scheduling, such as data placement, concurrent users, and master scheduling overhead. Based on our evaluation study, we present a formal model for capturing real-time MapReduce applications and the Hadoop platform. Using this model, we formulate the offline scheduling of real-time MapReduce jobs on a heterogeneous distributed Hadoop architecture as a constraint satisfaction problem (CSP) and introduce various search strategies for the formulation. We propose an enhancement of MapReduce’s execution model and a range of heuristic techniques for the online scheduling. We further outline some of our future directions that apply state-of-the-art techniques in the real-time scheduling literature

Measurement and Analysis of Ultrapeer-based P2P Search Networks

Unstructured Networks have been used extensively in P2P search systems today primarily for file sharing. These networks exploit heterogeneity in the network and offload most of the query processing load to more powerful nodes. As an alternative to unstructured networks, there have been recent proposals for using inverted indexes on structured networks for searching. These structured networks, otherwise known as distributed hash tables (DHTs), guarantee recall and are well suited for locating rare items. However, they may incur significant bandwidth for keyword-based searches. This paper performs a measurement study of Gnutella, a popular unstructured network used for file sharing. We focus primarily on studying Gnutella\u27s search performance and recall, especially in light of recent ultrapeer enhancements. Our study reveals significant query overheads in Gnutella ultrapeers, and the presence of queries that may benefit from the use of DHTs. Based on our study, we propose the use of a hybrid search infrastructure to improve the search coverage for rare items and present some preliminary performance results

A Declarative Perspective on Adaptive MANET Routing

In this paper, we present a declarative perspective on adaptable extensible MANET protocols. Our work builds upon declarative networking, a recent innovation for building extensible network architectures using declarative languages. We make the following contributions. First, we demonstrate that traditional MANET protocols, ranging from proactive, reactive, to epidemic can be expressed in a compact fashion as declarative networks, and we validate experimentally the use of declarative techniques to implement traditional MANETs emulated on a testbed cluster. Second, we show that the declarative framework enables policy-driven adaptation, in which a generic set of declarative rule-based policies are used to make runtime decisions on the choice of MANET protocols. Third, we present some initial ideas on fine-grained protocol composition and adaptation, where a typical MANET protocol can be composed and adapted from simpler components