Web Caching Research Articles

Utilizing Binary Rewriting for Improving End-Host Security

Conventional methods supporting Java binary security mainly rely on the security of the host Java Virtual Machine (JVM). However, malicious Java binaries keep exploiting the vulnerabilities of JVMs, escaping their sandbox restrictions and allowing attacks on end-user systems. Administrators must confront the difficulties and dilemmas brought on by security upgrades. On the other hand, binary rewriting techniques have been advanced to allow users to enforce security policies directly on the mobile code. They have the advantages of supporting a richer set of security policies and a self-constrained written code. However, the high administrative and performance overhead caused by security configuration and code rewriting have prevented rewriters from becoming a practical security tool. In this paper, we address these problems by integrating binary code rewriters with Web caching proxies and build the security system called PB-JARS, a Proxy-based JAva Rewriting System. PB-JARS works as a complimentary system to existing JVM security mechanisms by placing another line of defense between users and their end-user systems. It gives system administrators centralized security control and management for the mobile code and security policies. We evaluated PB-JARS using a real Java binary traffic model derived from analyzing real Web trace records. Our results show that adding binary rewriting to a Web caching system can be very efficient in improving end-host security at a low cost.

Distributed Selfish Caching

Although cooperation generally increases the amount of resources available to a community of nodes, thus improving individual and collective performance, it also allows for the appearance of potential mistreatment problems through the exposition of one node's resources to others. We study such concerns by considering a group of independent, rational, self-aware nodes that cooperate using online caching algorithms, where the exposed resource is the storage at each node. Motivated by content networking applications - including Web caching, content delivery networks (CDNs), and peer-to-peer (P2P) - this paper extends our previous work on the offline version of the problem, which was conducted under a game-theoretic framework and limited to object replication. We identify and investigate two causes of mistreatment: 1) cache state interactions (due to the cooperative servicing of requests) and 2) the adoption of a common scheme for cache management policies. Using analytic models, numerical solutions of these models, and simulation experiments, we show that online cooperation schemes using caching are fairly robust to mistreatment caused by state interactions. To appear in a substantial manner, the interaction through the exchange of miss streams has to be very intense, making it feasible for the mistreated nodes to detect and react to exploitation. This robustness ceases to exist when nodes fetch and store objects in response to remote requests, that is, when they operate as level-2 caches (or proxies) for other nodes. Regarding mistreatment due to a common scheme, we show that this can easily take place when the "outlier" characteristics of some of the nodes get overlooked. This finding underscores the importance of allowing cooperative caching nodes the flexibility of choosing from a diverse set of schemes to fit the peculiarities of individual nodes. To that end, we outline an emulation-based framework for the development of mistreatment-resilient distributed selfish caching schemes.

A clustering-based prefetching scheme on a Web cache environment

Web prefetching is an attractive solution to reduce the network resources consumed by Web services as well as the access latencies perceived by Web users. Unlike Web caching, which exploits the temporal locality, Web prefetching utilizes the spatial locality of Web objects. Specifically, Web prefetching fetches objects that are likely to be accessed in the near future and stores them in advance. In this context, a sophisticated combination of these two techniques may cause significant improvements on the performance of the Web infrastructure. Considering that there have been several caching policies proposed in the past, the challenge is to extend them by using data mining techniques. In this paper, we present a clustering-based prefetching scheme where a graph-based clustering algorithm identifies clusters of “correlated” Web pages based on the users’ access patterns. This scheme can be integrated easily into a Web proxy server, improving its performance. Through a simulation environment, using a real data set, we show that the proposed integrated framework is robust and effective in improving the performance of the Web caching environment.

A Multi-Level Cache Model for Run-Time Optimization of Remote Visualization

Remote visualization is an enabling technology aiming to resolve the barrier of physical distance. While many researchers have developed innovative algorithms for remote visualization, previous work has focused little on systematically investigating optimal configurations of remote visualization architectures. In this paper, we study caching and prefetching, an important aspect of such architecture design, in order to optimize the fetch time in a remote visualization system. Unlike a processor cache or web cache, caching for remote visualization is unique and complex. Through actual experimentation and numerical simulation, we have discovered ways to systematically evaluate and search for optimal configurations of remote visualization caches under various scenarios, such as different network speeds, sizes of data for user requests, prefetch schemes, cache depletion schemes, etc. We have also designed a practical infrastructure software to adaptively optimize the caching architecture of general remote visualization systems, when a different application is started or the network condition varies. The lower bound of achievable latency discovered with our approach can aid the design of remote visualization algorithms and the selection of suitable network layouts for a remote visualization system.

Cache architecture for on-demand streaming on the Web

On-demand streaming from a remote server through best-effort Internet poses several challenges because of network losses and variable delays. The primary technique used to improve the quality of distributed content service is replication. In the context of the Internet, Web caching is the traditional mechanism that is used. In this article we develop a new staged delivery model for a distributed architecture in which video is streamed from remote servers to edge caches where the video is buffered and then streamed to the client through a last-mile connection. The model uses a novel revolving indexed cache buffer management mechanism at the edge cache and employs selective retransmissions of lost packets between the remote and edge cache for a best-effort recovery of the losses. The new Web cache buffer management scheme includes a dynamic adjustment of cache buffer parameters based on network conditions. In addition, performance of buffer management and retransmission policies at the edge cache is modeled and assessed using a probabilistic analysis of the streaming process as well as system simulations. The influence of different endogenous control parameters on the quality of stream received by the client is studied. Calibration curves on the QoS metrics for different network conditions have been obtained using simulations. Edge cache management can be done using these calibration curves. ISPs can make use of calibration curves to set the values of the endogenous control parameters for specific QoS in real-time streaming operations based on network conditions. A methodology to benchmark transmission characteristics using real-time traffic data is developed to enable effective decision making on edge cache buffer allocation and management strategies.

Automatic Detection of Shared Fragments in Large Collections of Web Pages and its Applications

To reduce network-related delays in serving dynamic web pages, various approaches have been proposed. However, one of the common fundamental problems encountered in some representatives of them is how to automatically find shared fragments in large numbers of web pages. Besides, this problem is also encountered in studies of web content characteristics at fragment granularity. This paper gives a formal definition of the problem, presents an efficient and scalable algorithm for it, and introduces the applications of the algorithm. In the problem definition, we introduce the notion of compound fragment, and our definition of maximal shared fragment captures the real characteristics of fragments that are appropriate for delivery and caching individually. Our algorithm has two unique features: (1) it is able to find real maximal shared fragments (2) it is able to effectively handle large collections of web pages by utilizing database techniques. The algorithm has been implemented and applied to 16 large sets of web pages. The experiments show that the algorithm can effectively handle large numbers of web pages, and can provide significant bandwidth saving and latency reduction when used in fragment-based web caching.

DESIGN AND IMPLEMENTATION OF A P2P COOPERATIVE PROXY CACHE SYSTEM

In this paper, we design and implement a P2P cooperative proxy caching system based on a novel P2P cooperative proxy caching scheme. To effectively locate the cached web documents, a TTL-based routing protocol is proposed to manage the query and response messages in the P2P cooperative proxy cache system. Furthermore, we design a predict query-route algorithm to improve the TTL-based routing protocol by adding extra information in the query message packets. To select a suitable cache replacement algorithm for the P2P cooperative proxy cache system, three different cache replacement algorithms, LRU, LFU and SIZE, are evaluated using web trace based performance studies on the implemented P2P cooperative proxy cache system. The experimental results show that LRU is an overall better cache replacement algorithm for the P2P proxy cache system although SIZE based cache replacement approach produces slightly better cache hit ratio when cache size is very small. The performance studies also demonstrate that the proposed message routing protocols significantly improve the performance of the P2P cooperative proxy cache system, in terms of cache hit ratio, byte hit ratio, user request latency, and the number of query messages generated in the proxy cache system, compared to the flooding based message routing protocol.

WWW traffic measure and its properties

We present a method to extract a time series (Number of Active Requests (NAR)) from web cache logs which serves as a transport level measurement of internet traffic. This series also reflects the performance or Quality of Service of a web cache. It has long-memory properties but is not self-similar and does not have a heavy-tailed distribution. However, the long-memory and autocorrelation structure of NAR are preserved through aggregation, that is the aggregated series has similar statistical properties to the original one. We call this property aggregation similarity. Aggregation similarity is a very useful property, which makes management of large data sets easier and speeds up the asymptotic properties of time series.

One Size Doesn't Fit All: Improving Network Qos Through Preference-Driven Web Caching

In order to combat Internet congestion Web caches use replacement policies that attempt to keep the objects in a cache that are most likely to get requested in the future. We adopt the economic perspective that the objects with the greatest value to the users should be in a cache. Using trace driven simulations we implement an incentive compatible market-based Web cache for servers to push content into a cache. This system decentralizes the caching process as servers provide information in the form of bids for space in the cache. Truthful information from the server on valuations of objects and predictions of hit rates is obtained. This information is used in filling the cache, which can provide increased aggregate value and differential quality of service to servers when compared to LFU and LRU.

Biased Replacement Policies for Web Caches: Differential Quality-of-Service and Aggregate User Value

Disk space in shared Web caches can be diverted to serve some system users at the expense of others. Cache hits reduce server loads, and if servers desire load reduction to different degrees, a replacement policy which prioritizes cache space across servers can provide differential quality-of-service (QoS). We present a simple generalization of least-frequently-used (LFU) replacement that is sensitive to varying levels of server valuation for cache hits. Through trace-driven simulation we show that under a particular assumption about server valuations our algorithm delivers a reasonable QoS relationship: higher byte hit rates for servers that value hits more. We furthermore adopt the economic perspective that value received by system users is a more appropriate performance metric than hit rate or byte hit rate, and demonstrate that our algorithm delivers higher social welfare (aggregate value to servers) than LRU or LFU.

Performance analysis of a client-side caching/prefetching system for Web traffic

Network congestion remains one of the main barriers to the continuing success of the Internet. For Web users, congestion manifests itself in unacceptably long response times. One possible remedy to the latency problem is to use caching at the client, at the proxy server, or within the Internet. However, Web documents are becoming increasingly dynamic (i.e., have short lifetimes), which limits the potential benefit of caching. The performance of a Web caching system can be dramatically increased by integrating document prefetching (a.k.a. ''proactive caching'') into its design. Although prefetching reduces the response time of a requested document, it also increases the network load, as some documents will be unnecessarily prefetched (due to the imprecision in the prediction algorithm). In this study, we analyze the confluence of the two effects through a tractable mathematical model that enables us to establish the conditions under which prefetching reduces the average response time of a requested document. The model accommodates both passive client and proxy caching along with prefetching. Our analysis is used to dynamically compute the ''optimal'' number of documents to prefetch in the subsequent client's idle (think) period. In general, this optimal number is determined through a simple numerical procedure. Closed-form expressions for this optimal number are obtained for special yet important cases. We discuss how our analytical results can be used to optimally adapt the parameters of an actual prefetching system. Simulations are used to validate our analysis and study the interactions among various system parameters.

A birth–death model for Web cache systems: Numerical solutions and simulation

In this paper, we study Web cache hit rates by introducing a birth–death model. A system consisting of a single Web server with a single cache stores Web pages that are classified as hot pages (popular pages) and cold pages (less popular pages). Given requested probabilities for each class, the stochastic model provides the mean hit rate for a random replacement algorithm and the upper and low bounds for other algorithms. Numerical results from the analysis are validated using the output of simulation programs that utilize the LRU algorithm.

Exploiting client caches to build large Web caches

New demands brought by the continuing growth of the Internet will be met in part by more effective and comprehensive use of caching. This paper proposes to exploit client browser caches in the context of cooperative proxy caching by constructing the client caches within each organization (e.g., corporate networks) as a peer-to-peer (P2P) client cache. Via trace-driven simulations we evaluate the potential performance benefit of cooperative proxy caching with/without exploiting client caches. We show that exploiting client caches in cooperative proxy caching can significantly improve performance, particularly when the size of individual proxy caches is limited compared to the universe of Web objects. We further devise a cooperative hierarchical greedy-dual replacement algorithm (Hier-GD), which not only provides some cache coordination but also utilizes client caches. Through Hier-GD, we explore the design issues of how to exploit client caches in cooperative proxy caching to build large Web caches. We show that Hier-GD is technically practical and can potentially improve the performance of cooperative proxy caching by utilizing client caches.

Protect your users against the latest web-based threat: malicious code on caching servers [Your Internet Connection

Internet security threats are continually evolving as hackers try to stay ahead of countermeasures. In the last two years, a growing number of hackers have shifted their focus from straight-on firewall assaults and virus-laden emails - although these threats are not entirely things of the past - to Web-based attacks that expose Web site visitors to spyware, phishing scams, viruses, trojans, and other malicious code. An especially insidious new threat to Web users is the existence of malicious content residing in cached Web pages on storage and caching servers, such as those used by leading search engine providers, Web 2.0 sites, and Internet service providers (ISPs). This paper discusses the step-by-step process describing the infection method using search engine caching servers. The three examples of the type of Web threat, based on a recent analysis of Web pages on public storage and caching servers of three popular search engine providers are presented

A case for Passive Application Layer Multicast

Over the last few years, application-layer multicast (ALM) has emerged as a plausible solution for supporting group-oriented applications. However, ALM suffers from inefficiency due to its reliance on end hosts and potentially significant changes at both the server and client applications. In this paper, we propose an approach, PALM (Passive Application Layer Multicast), that removes the need for changes to the server or client applications while allowing for dynamic discovery of supporting network devices and client-side OS modules. The passive nature of the approach comes from the fact that bandwidth savings occur transparently with zero required modifications to the networking environment, similar to approaches such as web caching. We demonstrate the performance improvements of PALM relative to ALM and compare the benefits versus network-level multicast and separate unicast approaches through both simulation and experimental studies.

Efficient and Tailored Resource Management for the P2P Web Caching

While web proxy caching is a widely deployed technique, the performance of a proxy cache is limited by the local storage. Some studies have addressed this limitation by using the residual resources of clients via a p2p method and have achieved a very high hit rate. However, these approaches treat web objects as homogeneous objects and there is no consideration of various web characteristics. Consequently, the byte hit rate of the system is limited, external bandwidth is wasted, and perceived user latency is increased. The present paper suggests an efficient p2p based web caching technique that manages objects with different policies so as to exploit the characteristics of web objects, such as size and temporal locality. Small objects are stored alone whereas large objects are stored by dividing them into numerous small blocks, which are distributed in clients. On a proxy cache, header blocks of large objects take the place of objects themselves and smaller objects are cached. This technique increases the hit rate. Unlike a web cache, which evicts large objects as soon as possible in the case where clients fulfill the role of backup storage, large objects are given higher priority than small objects in the proposed approach. This maximizes the effect of hits for large objects and thereby increases the byte hit rate. Furthermore, we construct simple latency models for various p2p based web caching systems and analyze the effects of the proposed policies on these systems. We then examine the performances of the efficient policies via a trace driven simulation. The results demonstrate that the proposed techniques effectively enhance web cache performance, including hit rate, byte hit rate, and response time.

Cooperative Proxy Caching for Wireless Base Stations

This paper proposes a mobile cache model to facilitate the cooperative proxy caching in wireless base stations. This mobile cache model uses a network cache line to record the caching state information about a web document for effective data search and cache space management. Based on the proposed mobile cache model, a P2P cooperative proxy caching scheme is proposed to use a self‐configured and self‐managed virtual proxy graph (VPG), independent of the underlying wireless network structure and adaptive to the network and geographic environment changes, to achieve efficient data search, data cache and date replication. Based on demand, the aggregate effect of data caching, searching and replicating actions by individual proxy servers automatically migrates the cached web documents closer to the interested clients. In addition, a cache line migration (CLM) strategy is proposed to flow and replicate the heads of network cache lines of web documents associated with a moving mobile host to the new base station during the mobile host handoff. These replicated cache line heads provide direct links to the cached web documents accessed by the moving mobile hosts in the previous base station, thus improving the mobile web caching performance. Performance studies have shown that the proposed P2P cooperative proxy caching schemes significantly outperform existing caching schemes.

Mitigating the gateway bottleneck via transparent cooperative caching in wireless mesh networks

Wireless mesh networks (WMNs) have been proposed to provide cheap, easily deployable and robust Internet access. The dominant Internet-access traffic from clients causes a congestion bottleneck around the gateway, which can significantly limit the throughput of the WMN clients in accessing the Internet. In this paper, we present MeshCache, a transparent caching system for WMNs that exploits the locality in client Internet-access traffic to mitigate the bottleneck effect at the gateway, thereby improving client-perceived performance. MeshCache leverages the fact that a WMN typically spans a small geographic area and hence mesh routers are easily over-provisioned with CPU, memory, and disk storage, and extends the individual wireless mesh routers in a WMN with built-in content caching functionality. It then performs cooperative caching among the wireless mesh routers. We explore two architecture designs for MeshCache: (1) caching at every client access mesh router upon file download, and (2) caching at each mesh router along the route the Internet-access traffic travels, which requires breaking a single end-to-end transport connection into multiple single-hop transport connections along the route. We also leverage the abundant research results from cooperative web caching in the Internet in designing cache selection protocols for efficiently locating caches containing data objects for these two architectures. We further compare these two MeshCache designs with caching at the gateway router only. Through extensive simulations and evaluations using a prototype implementation on a testbed, we find that MeshCache can significantly improve the performance of client nodes in WMNs. In particular, our experiments with a Squid-based MeshCache implementation deployed on the MAP mesh network testbed with 15 routers show that compared to caching at the gateway only, the MeshCache architecture with hop-by-hop caching reduces the load at the gateway by 38%, improves the average client throughput by 170%, and increases the number of transfers that achieve a throughput greater than 1 Mbps by a factor of 3.

Periodic cache replacement policy for dynamic content at application server

Web caching has been widely adopted to improve server responsiveness without resorting to costly infrastructure overhauls. However, due to the need to support real-time transactions and content customization, an increasing proportion of web pages contain fragments that are dynamically generated, typically results of database queries, rendering whole-page caching at browser or proxy level inappropriate. A promising approach has been to place dynamic fragments in a web application server cache for multiple web requests. In this paper, we propose a periodic cache replacement policy for dynamic web content at application server. Since the content of a dynamically generated web fragment could become stale, the value of a cached copy of the fragment will likely decrease as updates accumulate at the back-end database. Constantly replacing the cached copy of the fragment will increase its freshness and value, yet will also incur a high cache replacement cost. In addition, not all fragments are equally important to various applications and it is preferable to cache mission-critical fragments. The decision problem then consists of what fragments should be selected to cache and how frequently the cache should be replaced so that the total cache benefits per unit time is maximized. Numerical and simulation experiments show that the periodic cache replacement policy is robust and effective in handling dynamic content.

A Parallel Network Emulation Method for Evaluating the Correctness and Performance of Applications

Network emulation system constructs a virtual network environment which has the characteristics of controllable and repeatable network conditions. This makes it possible to predict the correctness and performance of proposed new technology before deploying to Internet. In this paper we present a methodology for evaluating the correctness and performance of applications based on the PARNEM, a parallel discrete event network emulator. PARNEM employs a BSP based real-time event scheduling engine, provides flexible interactive mechanism and facilitates legacy network models reuse. PARNEM allows detailed and accurate study of application behavior. Comprehensive case studies covering bottleneck bandwidth measurement and distributed cooperative web caching system demonstrate that network emulation technology opens a wide range of new opportunities for examining the behavior of applications.