Browsing by Author "Liao, WK"

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Architecture of proxy partial caching using HTTP for supporting interactive video and cache consistency
(2002)
Liao, WK
;
Shih, PH
;
電信工程研究所
;
Institute of Communications Engineering
Proxy partial caching, e.g. segment-based proxy caching or proxy prefix caching, partitions the object into non-overlapping pieces. The proxy cache then treats each piece as an individual file when performing caching and replacing. Upon receipt of request to the object, the proxy cache delivers the cached portion to the client immediately to mask the start-up delay. However, two architectural challenges are confronted when implementing this technique in the web proxy software, e.g., Squid cache. The first challenge is related to caching video streams. Although not until recently, HTTP is recognized as an efficient method to support interactive video, many fundamental issues are still required to be solved. To this end, we propose an approach of segment-based video streams retrieval and caching via HTTP byte-range requests to further mask the possible start-up delay, enhance the interactive function "pause", and simplify the web proxy cache design. Proxy partial caching introduces the second architectural challenge called dirty-initial-segments problem, i.e. cached portion in the proxy cache is inconsistent with the original in the server. If this happens, the cached portion already delivered to the client cannot be concatenated with the latter portion from the server. To relieve this problem, we propose a novel algorithm called validating upon partial replacement, which synchronizes the operations of proactive consistency validation, partition and replacement performed upon an object. We show that our proposed algorithm bears the merit of controllable chance to disturb users, easily embedding into the existing web proxy cache with minimum modification, and improving the cache performance.
Flow control for ABR dispersity multicasting
(2000)
Liao, WK
;
Esfahanian, AH
;
Ni, LM
;
電信工程研究所
;
Institute of Communications Engineering
Dispersity multicasting is an extension of dispersity routing for multicast communication. In dispersity multicasting, m are-disjoint subtrees are used for source-destinations message delivery. If the bottleneck how control is applied to each of the m are-disjoint subtrees, there might still exist extra bandwidth for the multicast communication. To exploit the extra bandwidth, we introduce the concept of virtual connections. In this paper, we design a pow control algorithm for the available-hit-rate dispersity multicasting with two are-disjoint subtrees and one virtual connection. Issues for applying the algorithm to ATM networks are discussed. Simulation studies show that, in general, our algorithm enhances the throughput of dispersity multicasting.
Proxy prefetch and prefix caching
(2001)
Liao, WK
;
King, CT
;
電信工程研究所
;
Institute of Communications Engineering
Proxy prefetch caching aims to reduce the latency in serving web requests by prefetching objects into the proxy cache in anticipation that they might be requested. Thus, when the clients actually request them, these objects can be served directly from the proxy cache without having to be fetched all the way from the remote server A key component in proxy prefetch caching is the mechanism to determine the profitability of prefetching. A good prefetch advisor must consider not only factors such as the request probability of the prefetched objects, the network bandwidth, and object size, but also the cache space and those objects already in the cache. A unified framework is therefore needed, under which the prefetch advisor can judge whether prefetching some objects by replacing some other objects in the cache can lead to a reduction in the average user access time. In this paper we introduce a framework that unifies prefetch caching and cache replacement with a single index called object profit. The proposed framework is very general that it can be applied to almost any type of web objects, and it considers network bandwidth, cache capacity and replacement, object size, and analysis simplicity together We will derive the object profit mathematically, and then discuss how to apply the framework in practice. The proposed scheme is evaluated with simulation. As the simulation shows, the latency reduction by using the proposed framework can be maximized.