Research And Implementation Of Streaming Media Proxy Cache

With the continues development of Internet technology, the simple information such as texts, images and sounds can not match users' requirements, a new multimedia information composed of audio, video and dates is taking the place. The streaming media has larger data size and must be delivered in high speed; so it will consume the bandwidth resources. These characters make the Internet resources cannot meet its requirement. The conflicts between limited Internet's resources and wide application of streaming media are more serious, it id an exigent subject to save the internet resource and ensure the application of streaming media. The stream proxy is the key to resolve these problems.The stream proxy cache technology is developed from web proxy cache technology, web proxy cache technology is the most effective mechanism and mostly used in WWW service. Web proxy cache method fits for wholly save little files, but streaming media files are often very big, range from several hundred MB to several GB and are unfit for wholly save in proxy cache, so we have to take some strategies.In this paper, three strategies are used to manage proxy cache system, they are prefix cache, variant-length based segment cache (also called suffix cache) and dynamic cache respectively. These strategies form some relations, dispatching proxy cache space by the popularity of the media can greatly improve the usage rate of proxy cache system and therefore improve the service quality of the proxy. Meanwhile, we divide the media into two parts during the transmission for sake of starting time and date transmission stability; the former small in size is called prefix, the later large in size is called suffix. The prefix is stored in proxy cache, this part is delivered to the client immediately when requested, then, the proxy requests the suffix from the original server and delivers the suffix to the client. This method resolves the problems of starting delay time and date smooth efficiently.Variant-length based segment is a method that divides the date coming from the server into length fixable blocks. The origin block (prefix) contains certain blocks and the first segment equals to the origin segment in blocks count, the later segments are double of their previous segment.The prefix of any media can be stored in the proxy, and the prefix cache can only be replaced by other medias' prefix. As to the variant-length based segment, it depends on the popularity of the segment to decide storing it or not. The popularity has relations with the length and the visited number of the segment, the long of the length, the little of the popularity; the large the visited number, the large of the popularity.The replacement algorithm of proxy cache is segment-based replacement and LRU replacement policy. Calculate the cache value of stored parts of the media, and then sort all replaceable segments by the cache value from little to large. The first place segment is selected and its latest segment is removed from proxy cache. If the disk cache spaces are insufficient, revalue the replaced media's cache value (it increases when the saved length shorten), reform the queue and go on replacement process until the system gets enough disk space.Dynamic cache ensures the continuous services for the clients, its length must hold integer blocks and can accumulate the whole line of a batch. The server is the consumer of the cache space and producer of data content, the clients are the consumer of the data content and the producer of the cache space, signals used to mark the state of all proxy resources are the insurance of the services for the clients. There were clients drop out the batch during the process and only one left to be served, the proxy withdraws the dynamic cache, delivers the regular channel to the client directly. The dynamic cache policy reduces the request for the client cache, and makes it unnecessary for the client to hold two simultaneous streams.Network data transmitting methods are confined to unicast, multicast and broadcast, in this paper we depend on dynamic cache, use the strategy of one unicast from server to proxy and multiple unicast from proxy to clients, it just like the multicast from server to clients. This strategy is called application-level multicast It can be realized easily and low request on clients, but this method consumes very large network resources from proxy to clients, so it should be used at the position near the clients.We make use of RTSP protocol as the stream service protocol. RTSP is an application-level protocol for control over the delivery of data with real-time properties. It provides VRC functions, such as play, pause, playback etc. This protocol is intended to control multiple data delivery over the network. The application-level multicast strategy forbids the proxy to use pause, view speed and view back functions. The transition of stream data is not confined on network protocol, it can use either RTP (UDP)/RTCP (UDP) protocol or RTSP (TCP) entity to deliver the data. This system also has HTTP proxy functions, it main purpose is to response the hyperlink of the web pages, it dose not consider web cache functions. Our works do contributes in these fields:(1) Study and realize the transmission of multimedia stream and resolves the problems of starting delay time and date smooth efficiently.(2) Realize the dynamic cache strategy, improves the hit efficiency of the stream server.(3) Realize the multimedia stream proxy system based on "prefix+surfix+dynamic cache", which is serving in the VOD system of ZIBO POLICE.