Electrical computers and digital processing systems: multicomput – Computer-to-computer protocol implementing – Computer-to-computer data streaming
Reexamination Certificate
1998-03-25
2002-08-06
Luu, Le Hien (Department: 2152)
Electrical computers and digital processing systems: multicomput
Computer-to-computer protocol implementing
Computer-to-computer data streaming
C709S203000, C709S224000, C709S232000, C709S233000, C714S748000
Reexamination Certificate
active
06430620
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a data transfer method and a system in a computer network to which are connected a number of computers, more specifically to a data transfer method of stream data continuous in time series and a system for it.
BACKGROUND OF THE INVENTION
With improvement of computer capability and generalization of connection to network of computers in recent years, there is a growing request for real time transfer of stream data through computer network. Stream data here means data continuous in time series such as image, sound, etc. This stream data is naturally incorporated in packets and transferred through a network. Here this data is called stream data regardless whether the data is handled in units of prescribed number of groups of data or handled in disregard of such units of group.
FIG. 14
shows an example of conventional stream data transfer system. This system is composed of a server
500
on the side providing data and a client
508
on the side receiving the supply of data, and the network
507
intervenes between the two. A conventional system will be further explained hereafter based on
FIG. 14
together with its procedure.
The server
500
is constructed as described below. Namely, as explained hereafter, when a request for start of transfer of stream data is given from the client
508
to the sever, this request is delivered to the start request processing means
516
through the packet receiving means
501
, and this start request processing means
516
starts the rate controlling means
505
. This rate controlling means
505
reads out stream data from the storing device
503
such as hard disc, etc., and stores it in the transmission buffer
504
temporarily.
A prescribed send rate is set in advance in said rate controlling means
505
. This send rate is determined according to the reproduction rate of the client
508
and the capacity available for transfer of the network. The stream data stored in the transmission buffer
504
is read out at said prescribed send rate based on the control of the rate controlling means
505
and transferred to the packet transmitting means
502
, and the packet transmitting means
502
sends out this stream data to the network
507
by incorporating it in packets.
On the other hand, the client
508
is constructed as described below. Namely, the data packets received from the network
507
are received by the packet receiving means
509
, and the packets are disassembled here to be stored on the receiving buffer
511
one after another. The data reproducing means
512
reads out the data stored on the receiving buffer
511
as above sequentially at prescribed reproducing ate and delivers it to a display unit.
To control the start of transfer, a transfer start requesting means
517
is provided on the client
508
side, and this transfer start requesting means
517
issues a request for start of transfer according to the operator's instructions. This request for start of transfer is delivered to the packet transmitting means
510
, incorporated into transfer start request packets here, and transferred to the server
500
through the network
507
. As a result, the start request processing means
516
of the server
500
starts the rate controlling means
505
to start data transfer as described above.
Such procedure is repeated for the transfer of stream data between the server and the client. However, a computer network generally produces a certain amount of packet loss depending on the state of the network concerned, while packet loss is produced in case of occurrence of an overflow of the receiving buffer due to shortage of processing capacity of the client's computer, or fluctuation of reproducing ate of stream data, etc.
Therefore, also on said conventional system, an arrangement is made for compensation in such case of data loss.
Namely, the loss rate reporting means
513
of the client
508
constantly monitors the receiving buffer
511
and, in case of occurrence of any data loss, reports data loss rate to the packet transmitting means. The packet transmitting means
510
prepares a rate change request packet including an address of the server
500
, an identifier to the effect that it is a send rate change request packet, and said loss rate, and then transmits the packet to the network.
The rate change request packet sent out this way is received by the packet receiving means
501
of the server
500
, is identified as a rate change request packet here, and then is delivered to the rate changing means
506
. This rate changing means
506
is provided, in the form of a table, with send rates corresponding the loss rate on said client
508
contained in said rate change request packet for example, and the rate changer
506
determines a new send rate by referring to this table, and transfers that send rate to the rate controlling means
505
. Upon receipt of this transfer, the rate controlling means
505
reads out the stream data from the transmission buffer
504
by lowering (or raising) send rate and delivers it to the packet transmitting means
502
.
However, in such conventional stream data transfer system, the send rate from the server
500
is lowered only after any loss of data is detected by the client
508
as described above. Therefore there is no way to reproduce any data once lost. In addition, the images fluctuates in case any data partly lost is reproduced.
FIG. 15
shows a method to transfer data other than stream data such as text data, for example, from the server
500
to the client
508
.
Namely, each time when data “Data” in units of prescribed size is transferred from the server
500
to the client
508
, an acknowledgement signal “Ack” is returned from the client
508
to the server
500
and, upon receipt of this acknowledgement signal “Ack”, the server sends out a new data “Data”.
According to this method, the client
508
does not return the acknowledgement signal “Ack” when it received a data with loss, making it impossible for the server to send out the next “Data”. In this state, a shortage of data is produced on the receiving buffer
511
because the next data is not transferred until a prescribed time To elapses, for example. As a result, the image stops or fluctuates.
The object of the present invention, proposed in view of said defects of the conventional stream data transfer system, is to provide a more reliable stream data transfer method and a system, by lowering the send rate from the server before any loss of data is produced on the buffer of the client. Another object of the present invention is to provide a stream data transfer method and a system that transmits the lost data again even there is data is lost in the buffer of the client.
Yet another object of the present invention is to provide a stream data transfer method and its system, capable of effectively achieving said object, even in a multicast transfer system for transferring one same data to a plural number of clients simultaneously from the server.
SUMMARY OF THE INVENTION
The present invention adopts the means described below to achieve said objects. First, the stream data transfer system of the present invention comprises a server
400
and a client
470
as described below. In said server
400
the stream data read out from the storing means (storing device
403
and transmission buffer
404
in
FIG. 1
) at prescribed rate based on the control of the rate controlling means
405
are incorporated into data packets at the packet transmitting means
402
. Next, the packets are transmitted to the client
470
through the network
300
. The packet receiving means
401
receives request from the client
470
.
Moreover, said client
470
receives, with the packet receiving means
410
, the stream data sent out at prescribed rate from said server
400
through the network
300
, stores it once on the receiving buffer
412
and reproduces it, and sends out necessary instruction to said server
400
from the packet transmitting means
411
.
In said system, the present inv
Hirayama Kazuhiko
Omura Takeshi
Luu Le Hien
Matsushita Electric - Industrial Co., Ltd.
McDermott & Will & Emery
Vaughn, Jr. William C.
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