QoS Based Research And Implementation Of Streaming Media Proxy Cache

The 21^st century is a time of digital information. With the developmentand wide application of internet technology, network TV, remote education,video meeting, broad-band TV and broadcasting as well as mobile andwireless multimedia services have been flourishing in full swing. Multimediainformation like video, audio, image and cartoon has become a part ofpeople's life. And the development of stream media technique can enableusers to view or listen to the multimedia files while downloading theminstead of waiting for the completion of downloading. Therefore, streammedia has the features of real time, high speed and broad band. Although thecurrent internet is exerting its efforts, it cannot provide reliable quality ofservice to avoid delay and packet loss. Users want to view complete, smoothand pleasing video, yet the problems such as getting stuck, delay and videoand audio quality vibration are still quite common. The contradiction betweenlimited network resource and wide application of stream media is becomingmore and more serious. In order to save network resource and guarantee theapplication of stream media at the same time, we should not only ensure theend-to-end QoS of stream media, but consider the overall performance of thesystem. This is a challenging research subject, while the stream media proxycache technique based on QoS is the key for settling this difficulty.In the route between video storage server and client side, proxy cacheis the partial or complete storage of some video targets near the local proxyserver of the client. Proxy cache saves the repeated application andtransmission of many available data, which in turn decreases main networkflow, reduces the network band width consumed by users, and relievesnetwork block. Especially for the expensive WAN communication, it cangreatly reduce the network band width costs and facilitate networkmanagement. Under the circumstance of cache hit, the proxy cache closer tothe client side can remarkably decreases the response delay to users' requests.What's more, as proxy cache uses less network flow, with the proxy cache,the user can obtain the target not hit within less time than he obtains thetarget without proxy cache. At the same time, proxy cache reduces the visittimes to server, which relieves the burden of server and improves itsperformance.This article comprehensively analyzes the factors affecting QoSproblems in stream media system. Based on the advantages of stream mediaproxy cache, after referring to available stream media proxy cache theoriesand C/S-mode QoS control system in conventional stream media proxy cachetechniques, it applies stream media proxy cache technique to conduct QoStreatment to stream media transmission system. It applies the stream mediaproxy cache strategies such as prefix cache, segment cache and dynamiccache to set partial proxy cache, integrates the multiple factors of QoSindexes such as band width, delay, delay vibration, packet loss rate and errorcontrol etc., and precisely calculates the capacity of stream media proxycache with enlightening means to guarantee the efficiency of stream mediaproxy cache. At the same time, it applies proxy cache's control on QoSindexes like packet loss rate, delay vibration and network block etc. to makeverification, and further puts forward the plan to use proxy cache to controlnetwork block. System efficiency is the most important index of systemperformance. Considering the QoS control indexes of stream media, thearticle makes research on the proxy cache strategy of stream media, andrealizes stream media proxy cache system based on prefix cache, segmentcache and dynamic cache. Comprehensively considering improving theperformance of the whole stream media system, it rationally distributesstream media proxy cache.The detailed contribution and research results of this paper are asfollows:(1) It provides overall introduction about corresponding stream mediatechniques and the QoS control system of stream media. After analysis on theQoS problems of stream media, the article introduces the basic theory ofstream media, transmission protocol as well as the parameters, indexes andinfluence factors of stream media QoS. And it also lists the current researchstate, advantages and disadvantages of C/S QoS control system. Thediscussion and analysis of these contents is the foundation of further research.(2) Based on the current research about C/S QoS control system ofstream media, it takes advantages of the merits of stream media proxy cache,and uses stream media proxy cache technique to conduct QoS treatment tostream media transmission system. Prefix cache can reduce start-up delay,and guarantee quality of service. Applying the stream media proxy cachestrategies of prefix cache, segment cache and dynamic cache to set partialproxy cache can effectively avoid unnecessary cache resource waste broughtabout by the added prefix cache in stream media proxy cache targeted toguarantee QoS. At the same time, it can also effectively ensure the QoS inC/S stream media transmission system when network transmission is inabnormal state.(3) As for the methods to guarantee QoS with proxy cache, it integratesmultiple factors of QoS indexes such as band width, delay, delay vibration,packet loss rate and error control etc. It precisely calculates the capacity ofstream media proxy cache with enlightening means so as to guarantee theefficiency of stream media proxy cache. i.e. it should meet the condition of kin∑λjFj (≥min). (Fj=Fj (k), which is the user's satisfaction extent to the No.j QoS factor;λj denotes the weight of the No. j QoS factor in stream mediatransmission. It reflects the importance of the factor in stream mediatransmission system;k denotes the proportion relation of proxy cache andcache length unit, and k≤kmax)(4) It applies proxy cache's control on QoS indexes like packet loss rate,delay vibration and network block etc. to make verification, and further putsforward the plan to use proxy cache to control network block. It mainlyincludes:(i) In time of network block, i.e. in time of packet loss, the block controlsystem (protocol part) can decide the selection of packet—compare the pvalue of data packet to decide whether the packet should be abandoned ornot.(ii) In proxy cache FIFO calculation means, increase time limitation ordecrease relative time extent according to block state so that proxy cache canabandon less useful data packet.(iii) Calculate the expected future network flow according to currentnetwork flow while in the application process so that the initial selection of kvalue can be more proper.(5) It introduces efficiency-based proxy cache management strategy, i.e.the management strategy applying prefix cache, segment cache and dynamiccache. At the same time it guarantees the QoS control indexes of streammedia, it can enhance the utilization rate of system resource and systemefficiency, and in turn improve the overall performance of system.For proxy cache management, this article takes three strategies, prefixcache, segment cache (suffix cache) and dynamic cache. The three strategiesare closely associated to each other. Viewing from the angle of mediapopularization, proxy cache space provided can greatly improve theutilization rate of proxy cache as well as the service quality to clients. Prefixcache effectively settles the problems of delay and data smoothing in thestarting phase, thus reduces start-up delay and guarantees quality of service.Segment cache is a highly-effective way. The cache capacity in segmentcache can be distributed according to the frequency requested by the user.Segment cache and prefix cache are both concluded in proxy cache. Dynamiccache is for the provision of continuous services to the users. The length ofcache is the integral times of segment number so that it can contain the firstuser and the last user in the same batch list. In the process of playing, someusers may quit in advance. If only one user remains in the list, dynamic cacheis cancelled automatically, and the data from server is transmitted to the userdirectly. Dynamic cache reduces the request to the cache at the client side,and the client side doesn't need to receive data from two channels at the sametime in time of patch transmission.On the basis of segment cache, dynamic cache can further improve theefficiency of proxy cache. Dynamic cache doesn't need to be stored in proxycache for long, while segment cache needs to be always stored in proxy cache.Efficiency of segment cache is improved through the earlier user request,while the efficiency of dynamic cache is improved through the real time userrequest. The algorithms of segment cache and dynamic cache are applied atthe same time to better improve the efficiency of proxy cache.(6) The transmission of network data mainly includes unicast, multicastand broadcast. This article applies dynamic cache to act as proxy fromunicast of server to multicast of users, just like the multicast to users fromserver. We also call this as applied multicast. This can be easily realized as itdoesn't have too many requests for client side. Yet as the network resource islargely consumed, it is suitable to the stream media proxy close to the clientside.(7) Proxy stream media adopts RTSP protocol. RTSP is the denotationand control protocol of media streaming, and is used to control thetransmission of real time data. It can provide VCR functions such as play,pause and playback etc. And it provides network remote control tomultimedia server. As applied multicast limits the proxy, so that the functionsof RTSP such as pause, speed and backward cannot be used. For thetransmission of video data, it can be realized through RTP (UDP)/RTCP(UDP) transmission, or real transmission of RTSP protocol. At the same time,the proxy also has the function of HTTP proxy mainly for responding thehyperlink of webpage. It doesn't have web cache system.The article applies stream media proxy cache technique to guaranteeQoS. It can not only screen network vibration and long delay of WAN, butgreatly decrease the broad band consumption on the remote video server andbackbone network if combined with adequate multicast technique, thus inturn reduce packet loss rate, avoid block and provide users with low-delay,low-costs and high-quality service. The performance of stream mediasystem is also very important. The application of stream media should notonly consider the QoS on the C/S side, but the overall performance of thesystem. System efficiency is the prime system performance index. Therefore,in consideration of the QoS control index of stream media, the articleapplies the cache management strategy of prefix cache, segment cache anddynamic cache to improve the overall efficiency of the system. Referring tothe operation principle of stream media server, and adopting RTSP protocolas stream transmission protocol, it guarantees the QoS in stream mediatransmission, and realizes the overall improvement of system efficiency.The research has important theoretical significance and application value.