Multimedia server

Details Multimedia server Multimedia server

1998-11-30

2001-10-09

Banankhah, Majid A. (Department: 2151)

Electrical computers and digital processing systems: multicomput

Computer-to-computer data routing

Least weight routing

C710S117000, C710S124000

Reexamination Certificate

active

06301604

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention generally relates to a server for providing multimedia information to a network and, more particularly, to techniques for efficiently transmitting a plurality of time-series multimedia applications in a time-division multiplex by controlling the assignment of a CPU (central processing unit) operation time to the transmitted applications.
2. Description of the Prior Art
Applications including video, animation and/or audio are hereinafter referred to as time-series multimedia applications. Compressed multimedia applications may be either transmitted directly as they are (direct transmission), or once stored in a storage device and then transmitted at constant rates (stored transmission).
In the direct transmission, the compressed applications are launched into a network regardless of the transmission band of the network, which may cause the transmission rate to exceed the transmission band variable with time, resulting in the destruction of transmitted data. For this reason, the direction transmission is possible only when the network transmission band is sufficiently higher than the transmission rate, in which there is no need of the present invention.
A transmission scheme of stored multimedia at a constant rate is described in “Video server software—Video Network File System,” IEICE (The Institute of Electronics, Information and Communication Engineers) trans. Vol. J-77-A, No. 9, pp. 1-8. In this system, stored applications are read out and transmitted at a constant rate. This system reads out a frame of data for each of stored applications to be transmitted for transmission. Assuming that two applications AP
1
and AP
2
are to be transmitted and that both the frame size of the two applications are 10 Kbps, if the applications AP
1
and AP
2
are to be transmitted at rates of 10 Kbps and 5 Kbps, respectively, then the system transmits one AP
1
frame per second and one AP
2
frame per two seconds. In this way, each application is transmitted at a constant rate as long as the total load on the CPU does not exceeds the processing capacity of the CPU and the total transmission rate dose not exceeds the transmission bandwidth of the network. However, These conditions are not always satisfied.
It is therefore an object of the invention to provide a method and a system which are used when actually measured transmission rates of a plurality of multimedia applications differ from required transmission rates for the applications and which are for allocating time slices of the CPU to the threads for transmitting the multimedia applications such that the applications are transmitted at the required transmission rate.
A reduction in the transmission rate of a thread causes a delay of transmission by the thread resulting in asynchronism among transmitted applications.
It is another object of the invention to provide a method of and a system for temporarily changing the allocation of the available time slices to the threads so as to resolve the a synchronism among transmitted applications.
It is another object of the invention to provide a method and a system which are used when the number of time slices available to the threads has decreased to be insufficient to transmit the applications to be transmitted and which adjust the allocation of the available time slices to the threads according to the priorities of the applications.
SUMMARY OF THE INVENTION
A method for transmitting multimedia applications including a video and an audio at respective adapted transfer rates in a server connected with a network is provided. The server operates on an operating system which permits a multithreading by allocating time slices to thread. The method comprises the steps of:
for each application, preparing data on a required transfer rate indicative of a permitted lowest transfer rate for the application;
generating threads for respective applications;
allocating an initial number of slices to each thread to let the threads transmit respective applications;
measuring a transfer rate of each thread at a time interval;
calculating a number of slices to be allocated to each thread such that the measured transfer rate of each thread (i.e., each application) becomes equal to the required transfer rate of the application transmitted by the thread; and
allocating the calculated number of slices to each thread.
The number of slices are calculated by multiplying a current number of slices allocated to each thread by a ratio of the required transfer rate to the measured transfer rate.
In response to a detection of a synchronism among the applications, a corrected number of slices are temporarily allocated to each thread such that the applications have been synchronized by the end of a subsequent time interval.
In response to a detection of a decrease in a total of the measured transfer rates, the system allocates less slices to applications of lower priorities and more slices to an application of a higher priority.
A method for transmitting data to a plurality of destinations in a server connected with a network is also provided. The method compres the steps of;
creating a thread to each destination; and
in response to a request from one of the thread, returning a unit of data to be preferably transmitted at a time of the request, wherein the step of returning a unit of data includes the step of:
in response to a detection that a difference between the time of the request and a time of last request from a thread different from the requesting thread is smaller than a value associated with an unoccupied period of a central processing unit of the server, returning a same unit of data as returned at the time of last request.


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