Antonio Carzaniga

Design and evaluation of a wide-area event notification service

The components of a loosely coupled system are typically designed to operate by generating and responding to asynchronous events. An event notification service is an application-independent infrastructure that supports the construction of event-based systems, whereby generators of events publish event notifications to the infrastructure and consumers of events subscribe with the infrastructure to receive relevant notifications. The two primary services that should be provided to components by the infrastructure are notification selection (i. e., determining which notifications match which subscriptions) and notification delivery (i.e., routing matching notifications from publishers to subscribers). Numerous event notification services have been developed for local-area networks, generally based on a centralized server to select and deliver event notifications. Therefore, they suffer from an inherent inability to scale to wide-area networks, such as the Internet, where the number and physical distribution of the services clients can quickly overwhelm a centralized solution. The critical challenge in the setting of a wide-area network is to maximize the expressiveness in the selection mechanism without sacrificing scalability in the delivery mechanism. This paper presents SIENA, an event notification service that we have designed and implemented to exhibit both expressiveness and scalability. We describe the services interface to applications, the algorithms used by networks of servers to select and deliver event notifications, and the strategies used to optimize performance. We also present results of simulation studies that examine the scalability and performance of the service.

A routing scheme for content-based networking

This work proposes a routing scheme for content-based networking. A content-based network is a communication network that features a new advanced communication model where messages are not given explicit destination addresses, and where the destinations of a message are determined by matching the content of the message against selection predicates declared by nodes. Routing in a content-based network amounts to propagating predicates and the necessary topological information in order to maintain loop-free and possibly minimal forwarding paths for messages. The routing scheme we propose uses a combination of a traditional broadcast protocol and a content-based routing protocol. We present the combined scheme and its requirements over the broadcast protocol. We then detail the content-based routing protocol, highlighting a set of optimization heuristics. We also present the results of our evaluation, showing that this routing scheme is effective and scalable.

Achieving scalability and expressiveness in an Internet-scale event notification service

This paper describes the design of <italic>S</italic>IENA, an Internet-scale event notification middleware service for distributed event-based applications deployed over wide-area networks. <italic>S</italic>IENA is responsible for <italic>selecting</italic> the notifications that are of interest to clients (as expressed in client subscriptions) and then <italic>delivering</italic> those notifications to the clients via access points. The key design challenge for <italic>S</italic>IENA is maximizing <italic>expressiveness</italic> in the selection mechanism without sacrificing <italic>scalability</italic> of the delivery mechanism. This paper focuses on those aspects of the design of <italic>S</italic>IENA that fundamentally impact scalability and expressiveness. In particular, we describe <italic>S</italic>IENAs data model for notifications, the covering relations that formally define the semantics of the data model, the distributed architectures we have studied for <italic>S</italic>IENAs implementation, and the processing strategies we developed to exploit the covering relations for optimizing the routing of notifications.

Designing distributed applications with mobile code paradigms

Large scale distributed systems are becoming of paramount importance, due to the evolution of technology and to the interest of market. Their development, however, is not yet supported by a sound teclmological and methodological background, as the results developed for small size distributed systems often do not scale up. Recently, mobile code languages (MCLs) have been proposed as a technological answer to the problem. In this work, -we abstract away from the details of these languages by deriving design paradigms exploiting code mobility that are independent of any particular technology. We present such design paradigms, together with a discussion of their features, their application domain, and some hints about the selection of the correct paradigm for a given distributed application.

Forwarding in a content-based network

This paper presents an algorithm for content-based forwarding, an essential function in content-based networking. Unlike in traditional address-based unicast or multicast networks, where messages are given explicit destination addresses, the movement of messages through a content-based network is driven by predicates applied to the content of the messages. Forwarding in such a network amounts to evaluating the predicates stored in a routers forwarding table in order to decide to which neighbor routers the message should be sent. We are interested in finding a forwarding algorithm that can make this decision as quickly as possible in situations where there are numerous, complex predicates and high volumes of messages. We present such an algorithm and give the results of studies evaluating its performance.

Design and evaluation of a support service for mobile, wireless publish/subscribe applications

This paper presents the design and evaluation of a support service for mobile, wireless clients of a distributed publish/subscribe system. A distributed publish/subscribe system is a networked communication infrastructure where messages are published by senders and then delivered to the receivers whose subscriptions match the messages. Communication therefore does not involve the use of explicit addresses, but rather emerges from the dynamic arrangement of publishers and subscribers. Such a communication mechanism is an ideal platform for a variety of Internet applications, including multiparty messaging, personal information management, information sharing, online news distribution, service discovery, and electronic auctions. Our goal is to support such applications on mobile, wireless host devices in such a way that the applications can, if they chose, be oblivious to the mobility and intermittent connectivity of their hosts as they move from one publish/subscribe access point to another. In this paper, we describe a generic, value-added service that can be used in conjunction with publish/subscribe systems to achieve these goals. We detail the implementation of the service and present the results of our evaluation of the service in both wireline and emulated wireless environments.

Content-Based Networking: A New Communication Infrastructure

We argue that the needs of many classes of modern applications, especially those targeted at mobile or wireless computing, demand the services of content-based publish/subscribe middleware, and that this middleware in turn demands a new kind of communication infrastructure for its proper implementation. We refer to this new communication infrastructure as content-based networking. The service model of this network must directly support the interface of an advanced content-based publish/subscribe middleware service. At the same time, the implementation must be architected as a true distributed network, providing appropriate guarantees of reliability, security, and performance. We do not propose content-based networking as a replacement for IP, nor do we advocate an implementation of a publish/subscribe middleware at the network level (i.e., within routers). Instead, we argue that content-based networking must be designed according to established networking principles and techniques. To this end, in this paper, we formulate the foundational concepts of content-based networking, and relate them to the corresponding concepts in traditional networking. We also briefly review our experience with content-based publish/subscribe middleware and suggest some open research problems in the area of content-based networking.

Security issues and requirements for Internet-scale publish-subscribe systems

Publish-subscribe is a communication paradigm that supports dynamic, many-to-many communications in a distributed environment. Content-based pub-sub systems are often implemented on a peer-to-peer infrastructure that enables information dissemination from information producers (publishers) to consumers (subscribers) through a subscription mechanism. In a wide-area pub-sub network, the pub-sub service must handle information dissemination across distinct authoritative domains, heterogeneous platforms and a large, dynamic population of publishers and subscribers. Such an environment raises serious security concerns. In this paper, we investigate the security issues and requirements that arise in an internet-scale content-based pub-sub system. We distinguish among those requirements that can be achieved with current technology and those that require innovative solutions.Both peer services and web services offer a perspective services in the role of resources that can be combined enable new capabilities greater than the sum of the parts However, current service composition solutions seem t support either highly dynamic discovery or else very loosel coupled service development, but not both. We propose facilitator servicemechanism that can leverage “reflected” XML-based specifications (borrowed from the web servic domain) to direct and enable coordinated sequences of me sage exchanges (conversations) between services. We tend the specification of a message exchange with the ab ity to specify transformations to be applied to both inbound and outbound documents. We call these extended mess exchanges transformational interactions . The facilitator service can use these transformational interactions to allow service developers to decouple internal and external in terfaces. This means that services can be developed a treated as pools of methods that can be composed dynam cally.

Issues in supporting event-based architectural styles

To address this issue, researchers in the field of software architecture are defining a number of languages and tools that support the definition and validation of the architecture of systems. Also, a number of architectural styles are being formalized. Each of them defines “a set of design rules that identify the kinds of components and connectors that may be used to compose a system or a subsystem, together with local or global constraints on the way the composition is done” [5]. The formalization of styles helps the understanding and categorization of existing architectures and supports developers in the definition of the structure of new systems.

Automatic workarounds for web applications

We present a technique that finds and executes workarounds for faulty Web applications automatically and at runtime. Automatic workarounds exploit the inherent redundancy of Web applications, whereby a functionality of the application can be obtained through different sequences of invocations of Web APIs. In general, runtime workarounds are applied in response to a failure, and require that the application remain in a consistent state before and after the execution of a workaround. Therefore, they are ideally suited for interactive Web applications, since those allow the user to act as a failure detector with minimal effort, and also either use read-only state or manage their state through a transactional data store. In this paper we focus on faults found in the access libraries of widely used Web applications such as Google Maps. We start by classifying a number of reported faults of the Google Maps and YouTube APIs that have known workarounds. From those we derive a number of general and API-specific program-rewriting rules, which we then apply to other faults for which no workaround is known. Our experiments show that workarounds can be readily deployed within Web applications, through a simple client-side plug-in, and that program-rewriting rules derived from elementary properties of a common library can be effective in finding valid and previously unknown workarounds.