1. Introduction Pervasive computing demands the all-encompassing exploitation of services inside the network. By services, we mean both the components of distributed applications and the glue that interconnects them as they function across the network. Services range from providing basic network reachability to creating overlay networks with enhanced qualities like predictable latencies and sustained bandwidths. Services also include instances of application building blocks, requiring processing and storage, judiciously placed in the network to control connection latencies and to achieve scale through load sharing. Such services may be simple format translators, interworking functions, or major subsystems for content distribution or Internet search, which are often regarded as applications. Composition via interconnection of services allows more sophisticated services and applications to be constructed hierarchically from more primitive ones. Since economics makes it unlikely that any single service provider will be able to provide all the connectivity, applications building blocks, processing, and storage resources to effectively deploy a globe-spanning application, the composition of services across independent providers is essential. This paper proposes a comprehensive reference model for composed services in support of pervasive computing.JAL Travel created a new service from pieces, some of which were provided by other third parties, such as Babelfish, and all of which need to run on machines interconnected across the network, spanning Internet Data Centre providers and Internet Service Providers. Herein lies the second challenge: the ability for third parties to discover components and to broker new services from constituent pieces, some of which may not even be aware of the composition in which they are participating. As the qualities of a composed service are no better than its weakest component, an essential need is for brokers to be able to verify the performance and behaviour of the assembled components, whether these underlying participants are aware of their role in compositions. If a component does not meet its performance or behavioural specification, it must be “composed out”, and a new instance from a different provider “composed in”. A third challenge for service providers is the need for an extensive set of new service composition management tools. From a provisioning viewpoint, sufficient instances of the components need to be placed at locations within the network to ensure scalable performance and high availability even in the face of site failures or network outages. Such placement also needs to ensure appropriate network and processing latencies to achieve adequate responsiveness for the supported applications. Such tools include: (A) A policy management mechanism: This would ensure that service providers are able to inform service composers about how their instances in their network should be used for providing fault tolerant and load balanced behavioural pervasive monitoring and measurement. (B) A proper infrastructure is needed to detect changing access patterns and shifting workloads, to drive redirection to unloaded service instances or to change the number and placement of deployed instances. Network topology-awareness is important, for availability as well as performance. Placement and connectivity issues are complicated since some service instances are anchored to fixed locations, while lighter weight services can be placed close to the user community.Further challenges arise when we consider user dynamics. Many foreign roamers like Ms. Tanaka converge in Salt Lake City, yielding flash crowds and over-utilized spectrum. We need new ways of efficiently allocating resources in the context of new service provider business models. 2. Technical Issues The scenario in the prior section can be understood along three dimensions in the choices in service composition: (a) what set of services to use for composition, (b) which service providers’ resources to use. In addition, we also have the issue of who makes these decisions. Considering these dimensions, the technical issues that must be addressed in a reference model for service composition are: – Trust management and behaviour verification: When multiple providers interact, it is important to establish mutual trust. This is not only for the purpose of user authentication and billing, but also to verify the behaviour of the components in composition. Does a component meet its promises in terms of functionality, protocols, performance, availability, or other properties? – Adapting to network dynamics: With network dynamics, workloads can shift, congestion can arise, and reachability to services can be lost. This implies the need for performance monitoring, modelling and prediction, and a performance-sensitive choice of providers and instances. We term this the service selection problem. In a multi-provider environment, different providers may experience different demands for resources due to user dynamics. Demand or utility-based resource allocation can be applied within a service provider to manage its instances. In the brokered model, it can be used to allocate resources across providers. In SAHARA, we are exploring two resource allocation mechanisms which are: Auctions allocate resources to consumers based on their bids, which represent the value of the good to them. Furthermore, the resource can be subdivided into units, and multiple bidders can beallocated the resource until the resource pool is exhausted. Auctions can occur in rounds, where the allocation determined by each round can be for some future time. Auction-based allocations in a multi-provider environment can provide the mechanism for demand-based resource allocation. For instance, in the MVNO scenario, spectrum resources could be auctioned off every few minutes to competing virtual operators based on their current user-load around coverage. Congestion pricing is an allocation mechanism that assigns scarce resources to consumers using the abstraction of price to moderate demand. During high demand, such a market ensures that the price increases. Only those consumers with the greatest need and having sufficient currency will obtain the needed resource. During low demand, the price drops, and access to the resource with be cheap and plentiful. This approach should yield an assignment of resources (supply) to the need (demand) that adapts to instantaneous demands. 3. Policy Management An advantage of cooperative composition is that each provider has visibility into its network of services, while a broker does not. The disadvantage of this distributed form of composition is the lack of central control over the composition that the broker enjoys. This disadvantage can be minimized if some form of distributed policy management is in place. Specifically, in cooperative composition, the service composition policies of one service provider can be made visible to and applied at distant service providers further along the composed path. Such policies may include which service instances are for primary use and which are solely for use in various failure modes, and policies that govern load balancing between instances. A case study involving this principle is the distributed application of policies in inter-domain routing on the Internet. The BGP protocol was not designed to allow local policies to be imposed at distant points in the network. The Internet infrastructure has been plagued of late with pathological routes that attempt to impose such interdomain routing policies by tricking distant service providers’ route selections. 4. Conclusion SAHARA is our evolving architectural prototype for the creation, placement, and management of services in next generation networks. Our goal is to enable end-to-end service composition withdesirable, predictable, and enforceable properties spanning multiple potentially distrusting service providers. We investigate two forms of service composition under different business models with varying degrees of cooperation and trust among providers. We classify component services and composed services into a layered hierarchy. The overarching themes in the various techniques and mechanisms that we use for composition include: (a) measurement-based adaptation through dynamic choice among service providers and service instances, (b) utility-based resource allocation for demand-driven load sharing across provider resources, and (c) a trust-but-verify approach to management of trust and behaviour verification when multiple providers interact to provide a composed service. From the above case study, answer all the following questions:The strategic role that information systems play in an organisation to attain competitive advantage is crucial to survive in a challenging business environment; however, it is the responsibility of management to ensure that the challenges faced are successfully overcome. Critically discuss the possible challenges faced by SAHARA and management’s responsibility in overcoming them.
Step By Step Answers with Explanation
SAHARA, as an architectural prototype for the creation, placement, and management of services in next-generation networks, faces several challenges that must be addressed for its successful implementation and operation. These challenges pertain to both technical and managerial aspects. Let's delve into these challenges and discuss the responsibilities of management in overcoming them.
1. Policy Management: SAHARA operates in a distributed and cooperative composition model. This means that each service provider has visibility into its network of services, but there is a lack of central control. Management must establish policies that govern service composition, load balancing, and resource allocation. These policies need to be communicated to distant service providers along the composed path to ensure that the composition meets desired criteria.
In conclusion, SAHARA's success relies on addressing both technical and managerial challenges. Management plays a critical role in overseeing trust, policy management, resource allocation, security, and coordination among service providers. They must adapt to dynamic network conditions and evolving business models to ensure that SAHARA can provide desirable, predictable, and enforceable services in the pervasive computing environment. Overcoming these challenges will be essential for SAHARA to attain its goals and provide competitive advantages to organizations and users in the ever-changing landscape of networked services.