Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1999-08-05
2002-09-17
Srivastava, Vivek (Department: 2611)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S236000, C725S094000, C709S219000, C710S057000
Reexamination Certificate
active
06452943
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a data server system for transferring video data or audio data.
2. Prior Art
In conventional video server systems, a plurality of computers are interconnected using a network. Each computer receives and reproduces video (or audio) in real time according to video (or audio) data received from another computer. Depending on the method used to transfer data, such systems can be classified into “push-type” systems and “pull-type” systems.
In a pull-type video server system, the transmitting computer (hereafter, “transmitter”) receives transfer requests (control data) from a receiving computer (hereafter, “receiver”), and transmits video data to the receiver. The receiver receives this video data and uses it to reproduce video. On the other hand, in a push-type video server system, the transmitter transmits video data to the receiver using a certain cycle. The receiver reproduces video in synchronization with this cycle. Note that while this specification refers to “video data”, the same techniques can be used to transfer audio data or a combination of video and audio data.
The following describes a pull-type video server system and a push-type video server system in detail with reference to FIGS.
1
~
5
and FIGS.
6
~
9
, respectively.
FIG. 1
is a block diagram showing the overall construction of a computer that can be used to construct a conventional pull-type video server system, while
FIG. 2
shows the transmission and reception of video data in a pull-type video server system. In this example, computers
500
and
600
are both equipped with the same functions, including transmission and reception functions for video data.
As shown in
FIG. 1
, the present video server system includes computer
500
, computer
600
, and network
550
. The computers
500
and
600
are connected via the network
550
. The computer
500
includes a video data receiving unit
501
, a reception buffer
502
, a request receiving unit
503
, a video data transmitting unit
504
, a magnetic disc drive device
505
, and a request transmitting unit
506
. In this description, the corresponding functions of the computer
600
are given corresponding reference numerals, as shown in FIG.
2
.
The following describes the transfer of video data with the computer
600
as the receiver and the computer
500
as the transmitter. As shown in
FIG. 2
, the request transmitting unit
606
of the receiver
600
first transmits a transfer request to the request receiving unit
503
of the transmitter
500
via the network
550
and the reception buffer
502
of the transmitter
500
. This transfer request has a predetermined format, and requests the transfer of a video data block (the video data being stored having been divided in a predetermined manner into a plurality of blocks) that forms part of the video data corresponding to the video images desired by the user of receiver
600
.
In the transmitter
500
, the request receiving unit
503
that received the transfer request gives instructions to the video data transmitting unit
504
. The video data transmitting unit
504
reads the video data block corresponding to the transfer request from the magnetic disc drive device
505
and transfers the read video data block to the reception buffer
602
of the receiver
600
.
In the receiver
600
, the video data receiving unit
601
reproduces the video data that has been transferred to the reception buffer
602
. At the same time, the request transmitting unit
606
transmits another transfer request to the request receiving unit
503
of the transmitter
500
so that the next video data block can be received.
The transmitter
500
and the receiver
600
in present video server system repeatedly perform the operations described above, and so transfer and reproduce video data.
In this kind of pull-type video server system, the request transmitting unit
606
monitors the expendable amount of data in the reception buffer
602
and adjusts the timing at which it transmits transfer requests to the transmitter
500
to ensure that underflows and overflows of video data do not occur in the reception buffer
602
. Here, “expendable data” refers to data in the reception buffer
602
that is yet to be reproduced. In this system, transfer requests are transmitted from the receiver
600
to the transmitter
500
until it appears that an overflow may occur in the reception buffer
602
, so that the receiver
600
will continue to receive video data. When it appears that the further reception of video data may cause an overflow in the reception buffer
602
, the request transmitting unit
606
temporarily stops transmitting transfer requests and thereby ensures that no overflow will occur.
The following describes the control procedures performed by the transmitter
500
and the receiver
600
to transfer video data in this way, and the changes in the amount of expendable data in the reception buffer
602
due to this control. This description refers to FIGS.
3
~
5
.
FIG. 3
is a flowchart showing the control procedure when the receiver
600
in a pull-type video server system (see
FIG. 2
) receives video data.
In the receiver
600
, a request is first received from the user and the request transmitting unit
606
transmits a transfer request to the transmitter
500
(S
501
).
A video data block is transmitted from the transmitter
500
to the reception buffer
602
of the receiver
600
in accordance with the transfer request. The reception buffer
602
is constantly monitored by the request transmitting unit
606
that judges whether an overflow may occur in the reception buffer
602
(S
502
).
If an overflow appears possible (S
502
:Yes), the processing stops at S
502
. However, if an overflow does not appear possible (S
502
:No), it is judged whether all of the video data corresponding to the user request has been received (S
503
).
If the transfer of video data is complete (S
503
:Yes), the processing ends. If not (S
503
:No), the request transmitting unit
606
transmits a transfer request for the video data block following the previously received video data block to the transmitter
500
(S
504
).
FIG. 4
is a flowchart showing the control procedure when the transmitter
500
in a pull-type video server system (see
FIG. 2
) transmits video data.
When transmitting data, the transmitter
500
first waits for a transfer request to arrive from the receiver
600
(S
601
).
A transfer request is received from the receiver
600
while the transmitter
500
is in this wait state. The request receiving unit
503
of the receiver
500
judges whether a transfer request has been received by constantly monitoring the reception buffer
502
(S
602
).
If a transfer request has not been received (S
602
:No), the processing returns to S
601
and the transmitter continues to wait for a transfer request to arrive. If a transfer request has been received (S
602
:Yes), the video data transmitting unit
504
transmits a video data block corresponding to the transfer request to the receiver
600
(S
603
).
Next, it is judged whether the transfer requested by the transfer request has been completed (S
604
). If not (S
604
:No), the processing returns to S
601
. If so (S
604
:Yes), the processing ends.
By having the receiver
600
and the transmitter
500
perform the processing shown in
FIGS. 3 and 4
, video data can be transferred while the amount of expendable data in the reception buffer
602
of the receiver
600
is monitored. This is described in more detail below.
FIG. 5
shows how the amount of expendable data in the reception buffer
602
of the receiver
600
changes over time when video data is transferred in the above pull-type video server system.
Video data is transmitted from the transmitter
500
to the receiver
600
in accordance with transfer requests issued by the receiver
600
. This video data accumulates in the reception buffer
602
(see
FIG. 2
) of the receiver
600
and increases the amount of expendable data in the reception
Price and Gess
Srivastava Vivek
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