Proxy Caching Research Articles

Network-aware partial caching for Internet streaming media

The delivery of multimedia over the Internet is affected by adverse network conditions such as high packet loss rate and long delay. This paper aims at mitigating such effects by leveraging client-side caching proxies. We present a novel cache architecture and associated cache management algorithms that turn edge caches into accelerators of streaming media delivery. This architecture allows partial caching of media objects and joint delivery from caches and origin servers. Most importantly, the caching algorithms are both network-aware and stream-aware; they take into account the popularity of streaming media objects, their bit rate requirements, and the available bandwidth between clients and servers. Using Internet bandwidth models derived from proxy cache logs and measured over real Internet paths, we have conducted extensive simulations to evaluate the performance of various cache management algorithms. Our experiments demonstrate that network-aware caching algorithms can significantly reduce startup delay and improve stream quality. Our experiments also show that partial caching is particularly effective when bandwidth variability is not very high.

Adaptive leases: A strong consistency mechanism for the world wide web

We argue that weak cache consistency mechanisms supported by existing Web proxy caches must be augmented by strong consistency mechanisms to support the growing diversity in application requirements. Existing strong consistency mechanisms are not appealing for Web environments due to their large state space or control message overhead. We focus on the lease approach that balances these trade-offs and present analytical models and policies for determining the optimal lease duration. We present extensions to the HTTP protocol to incorporate leases and then implement our techniques in the Squid proxy cache and the Apache Web server. Our experimental evaluation of the leases approach shows that: 1) our techniques impose modest overheads even for long leases (a lease duration of 1 hour requires state to be maintained for 1030 leases and imposes an per-object overhead of a control message every 33 minutes), 2) leases yields a 138-425 percent improvement over existing strong consistency mechanisms, and 3) the implementation overhead of leases is comparable to existing weak consistency mechanisms.

On scalable and locality-aware web document sharing

We propose a scalable Web document sharing infrastructure model called Browsers-Aware Proxy Server. In this design, a proxy server connecting to a group of networked clients maintains an index file of data objects of all clients’ browser caches. If a user request misses in its local browser cache and the proxy cache, the browsers-aware proxy server will search the index file attempting to find it in another client's browser cache before sending the request to an upper level proxy or the Web server. If such a request does hit in a remote client, this client will directly forward the data object to the requesting client; or the proxy server fetches the data object from this client and then forwards it to the requesting client. The contributions of this caching model are twofold. First, we show that the amount of sharable data in browser caches is significant and can be utilized for document sharing among clients to improve Web caching performance and scalability. Second, the browsers-aware model can effectively and further improve Web prefetching performance. The browsers-aware model and its supported prefetching technique build a strong locality-aware Internet environment to make Web accesses fast with low communication costs. Conducting trace-driven simulations, we show the effectiveness of the browsers-aware model, and its unique advantages to facilitate prefetching.

Scalable consistency maintenance in content distribution networks using cooperative leases

We argue that cache consistency mechanisms designed for stand-alone proxies do not scale to the large number of proxies in a content distribution network and are not flexible enough to allow consistency guarantees to be tailored to object needs. To meet the twin challenges of scalability and flexibility, we introduce the notion of cooperative consistency along with a mechanism, called cooperative leases, to achieve it. By supporting /spl Delta/-consistency semantics and by using a single lease for multiple proxies, cooperative leases allow the notion of leases to be applied in a flexible, scalable manner to CDNs. Further, the approach employs application-level multicast to propagate server notifications to proxies in a scalable manner. We implement our approach in the Apache Web server and the Squid proxy cache and demonstrate its efficacy using a detailed experimental evaluation. Our results show a factor of 2.5 reduction in server message overhead and a 20 percent reduction in server state space overhead when compared to original leases albeit at an increased interproxy communication overhead.

Exploiting high-level coherence information to optimize distributed shared state

InterWeave is a distributed middleware system that supports the sharing of strongly typed, pointer-rich data structures across a wide variety of hardware architectures, operating systems, and programming languages. As a complement to RPC/RMI, InterWeave facilitates the rapid development of maintainable code by allowing processes to access shared data using ordinary reads and writes.Internally, InterWeave employs a variety of aggressive optimizations to obtain significant performance improvements with minimal programmer effort. In this paper, we focus on application-specific optimizations that exploit dynamic high-level information about an application's spatial data access patterns and the stringency of its coherence requirements. Using applications drawn from computer vision, datamining, and web proxy caching, we illustrate the specification of coherence requirements based on the (temporal) concept of "recent enough" to use, and introduce two (spatial) notions of view s, which allow a program to limit coherence management to the portion of a data structure actively in use. Experiments with these applications show that InterWeave can reduce their communication traffic by up to one order of magnitude with minimum effort on the part of the application programmer.

Using caching for browsing anonymity

Privacy-providing tools, including tools that provide anonymity, are gaining popularity in the modern world. Among the goals of their users is avoiding tracking and profiling. While some businesses are unhappy with the growth of privacy-enhancing technologies, others can use lack of information about their users to avoid unnecessary liability and even possible harassment by parties with contrary business interests, and to gain a competitive market edge.Currently, users interested in anonymous browsing have the choice only between single-hop proxies and the few more complex systems that are available. These still leave the user vulnerable to long-term intersection attacks.In this paper, we propose a caching proxy system for allowing users to retrieve data from the World-Wide Web in a way that would provide recipient unobservability by a third party and sender unobservability by the recipient and thus dispose with intersection attacks, and report on the prototype we built using Google.

A LOW LATENCY PROXY PREFETCHING CACHING ALGORITHM

The Web proxy cache system was deployed to save network bandwidth, balance server load, and reduce network latency by storing copies of popular documents in the client and proxy caches for the Uniform Resource Locator (URL) requests. To solve the problem of the Web's slow end-user response time, a Web proxy caching and prefetching strategy has been developed and implemented by the auother to provide the users by the information they mostly likely want to browse in user profiles. This developed strategy uses the Reverse Aggressive technique for prefetching, which was proposed theortically. This developed strategy has been implemented with different cache sizes using a Web caching simulator. The tradional caching replacement policies such as Least-Recently-Used (LRU), Hybrid, and Size policies were already existed in this simultor. This simulator has been modified by the work in this paper such that the most recent replacement policies; Last-In-First-Out (LIFO), First-Try, Swapping and Place-Holder policies under infinite sized cache have been implemented. The performance measurements of the developed strategy have been studied using the tradional replacement policies, and the most recent replacement policies. Also, a comparative study has been done to clarify the benefits of the Reverse Aggressive caching prefetching algorithm with respect to the Fixed-Horizon caching prefetching algorithm with respect to the Reduced Latency (RL). According to the implementation results, it has been found that the average latency has been reduced at a higher degree by using the Reverse Aggressive cache prefetching strategy.

A site-based proxy cache

In traditional proxy caches, any visited page from any Web server is cached independently, ignoring connections between pages. And users still have co frequently visit indexing pages just for reaching useful informative ones, which causes significant waste of caching space and unnecessary Web traffic. In order to solve the above problem, this paper introduced a site graph model to describe WWW and a site-based replacement strategy has been built based on it. The concept of "access frequency" is developed for evaluating whether a Web page is worth being kept in caching space. On the basis of user's access history, auxiliary navigation information is provided to help him reach target pages more quickly. Performance test results have shown that the proposed proxy cache system can get higher hit ratio than traditional ones and can reduce user's access latency effectively.

Improving Internet archive service through proxy cache

Traditionally, file transfer protocol (FTP) servers are major archive providers and users apply the Archie server to locate FTP archives. With the extreme popularity of the WWW, Web servers are now important archive providers and users download archives via HTTP. To reduce HTTP traffic, proxy cache servers are deployed on the Internet. However, we find the hit rate of archives in cache servers is quite low. This study proposes a combination of caching and better searching mechanisms to alleviate the problem. We enable a proxy server to automatically collect WWW and FTP archives from its cache, organize them in the form of an FTP directory, and then offer the directory list to the Archie. Accordingly, users can find archives on WWW and FTP servers through the Archie, and they can directly download archives from the proxy server, thus improving the reuse of cached archives. A system was implemented and operated in a real environment to evaluate the approach and results are discussed.

Predicting Web Users' Next Access Based on Log Data

This article considers models that describe how people browse the Web. We restrict our attention to navigation patterns within a single site, and base our study on standard Web server access logs. Given a visitor's previous activities on the site, we propose models that predict their next page request. If the prediction is reasonably accurate, we might consider “prefetching” the page before the visitor requests it. A more conservative use for such predictions would be to simply update the freshness records in a proxy or network cache, eliminating unnecessary If-Modified-Since requests. Using data from the Web site for the Computing and Mathematical Sciences Research Division of Lucent Technologies (cm.bell-labs.com) we first evaluate the predictive performance of low-order Markov models. We next consider mixtures of first-order Markov models, achieving a kind of clustering of Web pages in the site. This approach is shown to perform well, while significantly reducing the space required to store the model. Finally, we explore a Bayesian approach using a Dirichlet prior on the collection of links available to a user at each stage in their travels through the site. We show that the posterior probabilities derived under this model are fairly close to the cross-validation estimates of the probability of success.

LoColms: an innovative approach of enhancing traditional classroom form of education by promoting web-based distance learning in the poorer countries.

There have been numerous attempts recently to promote technology based education (Shrestha, 1997) in the poorer third world countries, but so far all these have not provided a sustainable solution as they are either centered and controlled from abroad and relying solely on foreign donors for their sustenance or they are not web-based, which make distribution problematic, and some are not affordable by most of the local population in these places. In this paper we discuss an application, the Local College Learning Management System (LoColms), which we are developing, that is both sustainable and economical to suit the situation in these countries. The application is a web-based system, and aims at improving the traditional form of education by empowering the local universities. Its economy comes from the fact that it is supported by traditional communication technology, the public switching telephone network system, PSTN, which eliminates the need for packet switched or dedicated private virtual networks (PVN) usually required in similar situations. At a later stage, we shall incorporate ontology and paging tools to improve resource sharing and storage optimization in the Proxy Caches (ProCa) and LoColms servers. The system is based on the client/server paradigm and its infrastructure consists of the PSTN, ProCa, with the learning centers accessing the universities by means of point-to-point protocol (PPP).

Proxies + path prediction: improving Web service provision in wireless-mobile communications

Mobile computing is considered of major importance to the computing industry for the forthcoming years due to the progress in the wireless communications area. A proxy-based architecture for accelerating Web browsing in wireless customer premises networks is presented. Proxy caches, maintained in base stations, are constantly relocated to follow the roaming user. A cache management scheme is proposed, which involves the relocation of full caches to the most probable cells but also percentages of the caches to less likely neighbors. Relocation is performed according to the output of a user movement prediction algorithm based on a learning automaton. The simulation of the scheme shows considerable benefits for the end user.

Performance modeling and evaluation of Web systems with proxy caching

AbstractWith the rapid expansion of Internet use and the recent development of multimedia, improving the quality of the Internet is becoming a crucial issue. To construct a network system with high performance for cost, an effective analysis must be made of the characteristics of the traffic flowing on the network, the processing performance of the Web server, and the processing performance of the proxy server with caching functions, and the resources must be allocated with good balance. In this paper, we present a modeling and performance evaluation of an entire Web system, including the Web server and proxy server. In particular, this paper presents basic data on the processing performance of the caching function of the proxy server acquired by benchmarking. A model of processing performance is presented. Then, taking account of past results, a performance evaluation model for the entire Web based on the newly constructed model is presented. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(4): 94–106, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1161

Scalable proxy caching of video under storage constraints

Proxy caching has been used to speed up Web browsing and reduce networking costs. In this paper, we study the extension of proxy caching techniques to streaming video applications. A trivial extension consists of storing complete video sequences in the cache. However, this may not be applicable in situations where the video objects are very large and proxy cache space is limited. We show that the approaches proposed in this paper (referred to as selective caching), where only a few frames are cached, can also contribute to significant improvements in the overall performance. In particular, we discuss two network environments for streaming video, namely, quality-of-service (QoS) networks and best-effort networks (Internet). For QoS networks, the video caching goal is to reduce the network bandwidth costs; for best-effort networks, the goal is to increase the robustness of continuous playback against poor network conditions (such as congestion, delay, and loss). Two different selective caching algorithms (SCQ and SCB) are proposed, one for each network scenario, to increase the relevant overall performance metric in each case, while requiring only a fraction of the video stream to be cached. The main contribution of our work is to provide algorithms that are efficient even when the buffer memory available at the client is limited. These algorithms are also scalable so that when changes in the environment occur it is possible, with low complexity, to modify the allocation of cache space to different video sequences.

Implications of proxy caching for provisioning networks and servers

In this paper, we examine the potential benefits of Web proxy caches in improving the effective capacity of servers and networks. Since networks and servers are typically provisioned based on a high percentile of the load, we focus on the effects of proxy caching on the tail of the load distribution. We find that, unlike their substantial impact on the average load, proxies have a diminished impact on the tail of the load distribution. The exact reduction in the tail and the corresponding capacity savings depend on the nature of the workload and the percentile of the load distribution chosen for provisioning networks and servers-the higher the percentile, the smaller the savings. For workloads considered in this study, compared with over a 50% reduction in the average load, the savings in network and server capacity was only 20%-35% for the 99th percentile of the load distribution. We also find that while proxies can be somewhat useful in smoothing out some of the burstiness in Web workloads; the resulting workload continues, however, to exhibit substantial burstiness and a heavy-tailed nature. We identify one-time requests for large objects to be the limiting factor that diminishes the impact of proxies on the tail of load distribution. We conclude that, while proxies are immensely useful to users due to the reduction in the average response time, they are less effective in improving the capacities of networks and servers.

Optimal multicast smoothing of streaming video over the Internet

A set of applications such as Internet video broadcasts, corporate telecasts, and distance learning require the simultaneous streaming of video to a large population of viewers across the Internet. The high bandwidth requirements and the multi-timescale burstiness of compressed video make it a challenging problem to provision network resources for streaming multimedia. For such applications to become affordable and ubiquitous, it is necessary to develop scalable techniques to efficiently stream video to a large number of disparate clients across a heterogeneous Internet. In this paper, we propose to multicast smoothed video over an application-level overlay network of proxies, and to differentially cache the video at the intermediate nodes (proxies) in the distribution tree, in order to reduce the network bandwidth requirements of video dissemination. We formulate the multicast smoothing problem as an optimization problem, and develop an algorithm for computing the set of transmission schedules for the tree that minimize the peak rate and rate variability, given buffer constraints at different nodes in the tree. We also develop an algorithm to compute the minimum buffer allocation in the entire tree, such that feasible transmission to all the clients is possible, when the tree has heterogeneous rate constraints. We show through trace-driven simulations that substantial benefits are possible from multicast smoothing and differential caching, and that these gains can be realized even with modest proxy caches.

Limitations and benefits of cooperative proxy caching

Cooperating proxy caches are groups of HTTP proxy servers that organize to share cached objects. This paper develops analytical models for proxy cooperation which use speedup in user response time as the performance metric. Speedup expressions are derived for the cooperation upper bound, a proxy mesh, and a three-level proxy hierarchy. The equations compare fundamental design approaches by separating the proxy organization for object delivery from the mechanism for object discovery. Discovery mechanisms analyzed for the mesh and hierarchy models include ideal discovery, Internet cache protocol (ICP) query, and distributed metadata directories. Equations are evaluated using parameter estimates from experiments and from analysis of cache trace logs. Results indicate that proxy cooperation is marginally viable from the standpoint of average user response time, and that the miss penalty for the hierarchy renders it less viable than the mesh. Proxy cooperation can, however, reduce the variability in user response time and the number of long delays. A trace-driven simulation shows that caching constraints have little effect on cooperation performance due to request filtering by lower level caches.

UCFS - a novel User-space, high performance, Customized File System for Web proxy servers

Web proxy caching servers play a key role in today's Web infrastructure. Previous studies have shown that disk I/O is one of the major performance bottlenecks of proxy servers. Most conventional file systems do not work well for proxy server workloads and have high overheads. This paper presents a novel, User-space, Customized File System, called UCFS, that can drastically improve the I/O performance of proxy servers. UCFS is a user-level software component of a proxy server which manages data on a raw disk or disk partition. Since the entire system runs in the user space, it is easy and inexpensive to implement. It also has good portability and maintainability. UCFS uses efficient in-memory meta-data tables to eliminate almost all I/O overhead of meta-data searches and updates. It also includes a novel file system called Cluster-structured File System (CFS). Similarly to the Log-structured File Systems (LFS), CFS uses large disk transfers to significantly improve disk write performance. However, CFS can also markedly improve file read operations and it does not generate garbage. Comprehensive simulation experiments using five representative real-world traces show that UCFS can significantly improve proxy server performance. For example, UCFS achieves 8-19 times better I/O performance than the state-of-the-art SQUID server running on a Unix Fast File System (FFS), 4-7.5 times better than SQUID on asynchronous FFS, and 3-9 times better than the improved SQUIDML.

動画像品質調整機能を組み込んだプロキシキャッシングシステムの実装と評価(マルチメディア通信とQoS, VoIP, ストリーミング, 一般)

動画像品質調整機能を組み込んだプロキシキャッシングシステムの実装と評価(マルチメディア通信とQoS, VoIP, ストリーミング, 一般)

재생량에 기반한 연속미디어 데이터 프록시 캐슁 기법

연속미디어 데이터를 인터넷을 통해 서비스하기 위해서는 서버의 과부하, 네트워크의 혼잡, 사용자에 대한 응답시간 지연 등의 문제를 해결하여야 한다. 본 논문에서는 연속미디어 프록시 캐쉬에서 데이터를 관리하는 PPC(Popularity-based Prefix Caching) 기법을 제안한다. 사용자 접근 패턴을 반영하는 PPC 기법은 객체들의 앞부분 데이터를 그 객체의 인기에 비례하여 캐슁함으로써 사용자에 대한 초기지연시간을 감소시키고, 캐쉬 공간을 효율적으로 활용하고자 한다. 연속미디어에 대한 사용자 접근의 특성이 이산미디어와는 상이하다는 점을 고려하여, 연속미디어의 인기도를 더욱 정확하게 나타내기 위해서 각 연속미디어에 대한 사용자의 재생 데이터 양과 접근의 최근성을 반영하는 인기도를 제안한다. 그리고 제안하는 기법의 성능을 평가하기 위하여 인터넷 방송국 VOD 서버의 로그 데이터를 이용한 트레이스 기반 모의 실험을 수행하였다. 그 결과, PPC 기법은 BHR, 초기 지연 시간, 재배치의 측면에서 기존의 LRU, LFU 캐슁 기법들에 비하여 성능이 향상되었고, 특히, 초기 지연시간과 재배치 오버 헤드의 감소 측면에서 매우 우수한 성능을 보였다. In this paper, we propose a proxy caching scheme that stores a portion of a continuous media object or an entire object on the Internet. The proxy stores the initial fraction of a continuous media object and determines the optimal size of the initial fraction of the continuous media object to be cached based on the object popularity. Under the proposed scheme, the initial latency of most clients and the data transferred from a remote server can be reduced and limited cache storage space can be utilized efficiently. Considering the characteristics of continuous media, we also propose the novel popularity for the continuous media objects based on the amount of the data of each object played by the clients. Finally, we have performed trace-driven simulations to evaluate our caching scheme and the popularity for the continuous media objects. Through these simulations, we have verified that our caching scheme, PPC outperforms other well-known caching schemes in terms of BHR, DSR and replacement and that popularity for the continuous media objects based on the amount of the playback data can enhance the performance of caching scheme.