1 introduction
Along with networking development, backbone network and broadband networks turning on technology gradually maturing, a network video frequency transmission into Internet application luminescent spot. In order to enhance the video data in on-line transmission efficiency, and realizes the video frequency real-time broadcast, flowed the media technology the research and the application obtained the very big development.
And, flowed the media server technology to play the key role in the class media application.
The traditional network transmission data's method is document downloading: The user need preparation massive floppy disk space, and the flowered massive time waited for that downloading ended. But, when the data turns the magnanimous video data, is big in the data process load, the data volume of goods handled is high, video frequency broadcast timeliness, the customer connection request number is big, connection time long and so on some situations, the traditional server technology was already unable highly effective to satisfy the request. Facing such specification, this article from the CPU dispatch, the resource control memory allocation, the I/O main line manages these three aspects to embark, the synthesis has given one highly effective server design method, thus time effective enhancement video frequency class type transmission efficiency. This method also has the very strong extendibility, when server's CPU number increases, server's performance will be able to obtain the growth doubled and re-doubled.
2 class media server's design
2.1 class media server's function
Flows the media downloads the entire document completely before the broadcast, but starts the partial contents to store the memory, the data stream is momentarily transmits momentarily broadcasts.
Flows the class type transmission mode which the media server provides to have two kinds: The smooth class type transmission and the solid fashion type transmit two ways. The smooth class type transmission is smooth downloading, may watch the online media during the downloading document's user. The solid fashion type transmission and the smooth class type transmission is different, the solid fashion type transmission always real-time transmits, especially qualify scene event. Because the solid fashion type transmission must the accordant connection band width, this mean the picture quality the network speed to reduce worses.
When class type transmission, flows the media data to have timeliness, isochronism and so on essential feature, flows the period of service and the customer terminal must guarantee the synchronized relations between each kind of media, therefore, flows the media to transmit “the biggest time delay” rightly, “the time delay vibration” and so on QoS parameters have the strict request.
2.2 class media server agreement stack's design
In the TCP/IP reference model, transmission level communication protocol TCP and UDP cannot satisfy the class media transmission the QoS request. Because the TCP agreement uses the sliding window control mechanism, the data transfer controls the window dynamic start and the closure along with the class, satisfies the class media with difficulty real-time and the isochronal transmission request. The UDP agreement's connectionless characteristic can raise the transmission speed, although may satisfy the class media to a certain extent the timely request, but as a result of its unreliability, is also unable to satisfy the class media transmission the need.
In view of transmission level agreement contradiction, to realize the class media on IP real-time transmission broadcast, when design class media server needs (TCP/UDP) and between the application layer increases a correspondence key-course in the transmission level agreement. Is increasing the correspondence key-course, uses the corresponding live transmission agreement, including: Data stream part's live transmission agreement RTP (Real-time Transport Protocol), uses in the control section live transmission controlling agreement RTCP (Real-time Transport Figure 1 class media service agreement stack Streaming Protocol). The RTP agreement is mainly uses for to transmit the real-time class media information, the data newspaper mainly includes the multimedia data, as well as carries the load the time stamp, the atomic number and so on. The RTCP agreement's data newspaper mainly included the receive to receive some multimedia class the grade of service information, used to the server end feedback.
Flows media server's agreement stack as shown in Figure 1.
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