The rapid growth of time-critical information services and business-oriented applications is making quality of service (QoS) support increasingly important in content distribution. This paper investigates the problem of placing object replicas (e.g., web pages and images) to meet the QoS requirements of clients with the objective of minimizing the replication cost. We consider two classes of service models: replica-aware service and replica-blind service. In the replica-aware model, the servers are aware of the locations of replicas and can therefore direct requests to the nearest replica. We show that the QoS-aware placement problem for replica-aware services is NP-complete. Several heuristic algorithms for efficient computation of suboptimal solutions are proposed and experimentally evaluated. In the replica-blind model, the servers are not aware of the locations of replicas or even their existence. As a result, each replica only serves the requests flowing through it under some given routing strategy. We show that there exist polynomial optimal solutions to the QoS-aware placement problem for replicablind services. Efficient algorithms are proposed to compute the optimal locations of replicas under different cost models.

Abstract—Geographically replicating popular objects in the Internet speeds up content distribution at the cost of keeping the replicas consistent and up-to-date. The overall effectiveness of replication can be measured by the total communication cost consisting of client accesses and consistency management, both of which depend on the locations of the replicas. This paper investigates the problem of placing replicas under the widely used TTL-based consistency scheme. A polynomial-time algorithm is proposed to compute the optimal placement of a given number of replicas in a network. The new replica placement scheme is compared, using real Internet topologies and Web traces, against two existing approaches which do not consider consistency management or assume invalidation-based consistency scheme. The factors affecting their performance are identified and discussed. Index Terms—Replication, replica placement, TTL-based consistency, data consistency. 1

As the Internet continues to grow in size and popularity, web traffic and network bottlenecks are major issues in the network world. The continued increase in demand for objects on the Internet causes severe overloading in many sites and network links. Many users have no patience in waiting more than few seconds for downloading a web page. Web traffic reduction techniques are necessary for accessing the web sites efficiently with the facility of existing network. Web pre-fetching techniques and web caching reduces the web latency that we face on the internet today. This paper describes about the various prefetching and caching techniques, how they predict the web object to be pre-fetched and what are the issues challenges involved when these techniques are applied to a mobile environment.