Service-oriented computing is becoming an increasingly popular paradigm for modelling and building distributed systems in open and heterogeneous environments. However, proposed service-oriented architectures are typically based on centralised components, such as service registries or service brokers, that introduce reliability, management, and performance issues. This paper describes an approach to fully decentralise a service-oriented architecture using a self-organising peer-to-peer network maintained by service providers and consumers. The design is based on a gradient peer-to-peer topology, which allows the system to replicate a service registry using a limited number of the most stable and best performing peers. The paper evaluates the proposed approach through extensive simulation experiments and shows that the decentralised registry and the underlying peer-to-peer infrastructure scale to a large number of peers and can successfully manage high peer churn rates.

Mobile ad hoc networks rely on the opportunistic interaction of autonomous nodes to form networks without the use of infrastructure. Given the radically decentralized nature of such networks, their potential for autonomous communication is significantly improved when the need for a priori consensus among the nodes is kept to a minimum. This paper addresses an issue within the domain of semantic content discovery, namely, its current reliance on the preexisting agreement between the schema of content providers and consumers. We present OntoMobil, a semantic discovery model for ad hoc networks that removes the assumption of a globally known schema and allows nodes to publish information autonomously. The model relies on the randomized dissemination and replication of metadata through a gossip protocol. Given schemas with partial similarities, the randomized metadata dissemination mechanism facilitates eventual semantic agreement and provides a substrate for the scalable discovery of content. A discovery protocol can then utilize the replicated metadata to identify content within a predictable number of hops using semantic queries. A stochastic analysis of the gossip protocol presents the different trade-offs between discoverability and replication. We evaluate the proposed model by comparing OntoMobil against a broadcast-based protocol and demonstrate that semantic discovery with proactive replication provides good scalability properties, resulting in a high discovery ratio with less overhead than a reactive nonreplicated discovery approach.

Due to the heterogeneity of the environment, in which hosts may have different bandwidth capacities and network distances between hosts vary, current mesh-based multicast protocols for video streaming over the Internet tend to in efficiently utilise the available bandwidth and often transfer large amounts of data between distant hosts. This limits system throughput, which results in reduced video quality, and imposes significant costs on Internet service providers (ISPs) caused by network traffic outside a provider's own network. This paper presents MeshTV, a mesh-based peer-to-peer (P2P) multicast protocol for streaming live video from a transmitter to numerous viewers. MeshTV proposes an algorithm for adapting the mesh overlay in which nodes explore their possible neighbour nodes and select neighbours so that data throughput is optimised and data is transmitted between nearby (low-latency) nodes, typically within the same ISP thus reducing the costs to ISPs. Our evaluation demonstrates that the adaptation algorithm used in MeshTV can improve video streaming throughput by over 100 % and typically reduces the distances (network latencies) between interacting nodes by 50 % compared to unoptimised mesh overlays.

Designers face many system optimization problems when building distributed systems. Traditionally, designers have relied on optimization techniques that require either prior knowledge or centrally managed runtime knowledge of the system's environment, but such techniques are not viable in dynamic networks where topology, resource, and node availability are subject to frequent and unpredictable change. To address this problem, we propose collaborative reinforcement learning (CRL) as a technique that enables groups of reinforcement learning agents to solve system optimization problems online in dynamic, decentralized networks. We evaluate an implementation of CRL in a routing protocol for mobile ad hoc networks, called SAMPLE. Simulation results show how feedback in the selection of links by routing agents enables SAMPLE to adapt and optimize its routing behavior to varying network conditions and properties, resulting in optimization of network throughput. In the experiments, SAMPLE displays emergent properties such as traffic flows that exploit stable routes and reroute around areas of wireless interference or congestion. SAMPLE is an example of a complex adaptive distributed system.

CORBA, the Common Object Request Broker Architecture, defines a framework for developing object-oriented distributed applications.Unfortunately, current implementations of CORBA have not been designed with support for mobile computers in mind.Using CORBA in a mobile environment raises a number of problems due to hardware mobility and the characteristics of wireless networks.This paper identifies and discusses these problems and presents the design and implementation of our Architecture for Location Independent CORBA Environments (ALICE).ALICE allows CORBA objects running on mobile devices to interact transparently with objects hosted by off-the-shelf CORBA implementations.Importantly, ALICE allows server as well as client objects to reside on mobile hosts without relying on a centralised location register to keep track of their whereabouts.1 introduction CORBA, the Common Object Request Broker Architecture [7], from the Object Management Group (OMG), defines a framework for developing object-oriented distributed applications.CORBA is based on the clientserver paradigm and the most important component in the architecture is the Object Request Broker (ORB) which is responsible for relaying object invocations from clients to server objects.Initially, the CORBA standard made no provision for interoperability between ORBS supplied by different vendors.Later versions of the standard addressed this issue by defining a standard protocol for inter-ORB communication which is known as the General Inter-ORB Protocol (GIOP) [7, Chapter 131 and which can PeMkion to make digital or hard copies of all or part of this work t'or PCrSOnal Or ChirOOnl use is granted without fee provided that comicare not made or distributed for profit or commercial advarltage and that copies bear this notice and the f'ull citation on the first page.ho copy otheRvise, to republish, to post on servers or to redistribute to lists.rcquircs prior specific permission and/or a fee.