Server

Details Server Server

1997-03-04

2001-04-03

Rinehart, Mark H. (Department: 2756)

Electrical computers and digital processing systems: multicomput

Multicomputer synchronizing

C711S118000, C709S219000

Reexamination Certificate

active

06212571

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a server which transfers, for example, continuous data such as video data in response to a request from a client, and more particularly to a server effectively used with a communication system wherein a plurality of servers are coupled to each other by a network and continuous data of an image file or the like are stored discretely in the servers.
2. Description of the Related Art
Continuous data represented by video data are required to be transferred without interruption to a client. Japanese Patent Laid-Open Application No. Heisei 3-185948 or No. Heisei 6-236330 discloses a system which transfers video data via a network. Further, a server for use with a system of the type just mentioned is conventionally known and disclosed, for example, in Nikkei Electronics, No. 645, pp.133-141. The server disclosed in the document just mentioned will be hereinafter referred to as first prior art.
FIG. 8
shows a communication system in which the server of the first prior art Is employed. Referring to
FIG. 8
, the communication system shown includes a video server
101
for distributing video data, a plurality of clients
102
1
to
102
N
, and a network
103
which interconnects the video server
101
and the clients
102
1
to
102
N
. The video server
101
includes a file apparatus
111
for storing video data. The video data stored in the file apparatus
111
are read out by a file read-out section
112
and temporarily stored into a buffer
113
, and then sent out to the network
103
by a distribution section
114
.
If a request for video data is received from one of the clients
102
1
to
102
N
, then the video server
101
reads out relevant data from the file apparatus
111
and temporarily stores the data into the buffer
113
. It is assumed now that a request for video data is developed from the client
102
1
. The video data in the buffer
113
are successively sent to the distribution section
114
and then sent via the network
103
to and reproduced by the client
102
1
.
In the communication system employing the server of the first prior art, the buffer is used so that video data as continuous data may be distributed without interruption from the video server
101
to the clients
102
1
to
102
N
side, and the buffer capacity of the buffer
113
on the video server
101
side is set to a rather high capacity in order to reduce the buffer capacity on the clients
102
1
to
102
N
side. Accordingly, the video server
101
is constructed such that it need not access the file apparatus
111
every time a request is received from any of the clients
102
1
to
102
N
.
The communication system employing the server of the first prior art described above is subject to restriction in number of clients (
102
1
to
102
N
) to which video data are to be supplied from a relationship to an upper limit to the capacity of a work station which constructs the video server. In order to solve this problem, two countermeasures are available: one is to raise the upper limit to the capacity of a work station, and the other is to use a plurality of video servers which operate in parallel to each other. The countermeasure to raise the upper limit to the capacity of a work station requires development of a new server having a higher capacity. On the other hand, the countermeasure to use a plurality of video servers which operate in parallel to each other is advantageous in that existing comparatively inexpensive work stations can be used for the video servers.
FIG. 9
shows a system wherein a plurality of video servers operate in parallel to each other. The system will be hereinafter referred to as second prior art. In
FIG. 9
, like elements are denoted by like reference symbols to those of
FIG. 8
, and overlapping description of those elements is omitted herein to avoid redundancy. Referring to
FIG. 9
, the system shown includes a video server
121
which in turn includes totaling M first to Mth unit servers
122
1
to
122
M
. The unit servers
122
1
to
122
M
include, similarly as in the video server
101
of
FIG. 8
, file apparatus
111
1
to
111
M
, file read-out sections
112
1
to
112
M
, buffers
113
1
to
113
M
, and distribution sections
114
1
to
114
M
, respectively. Video data are stored discretely in units of a block in the file apparatus
111
1
to
111
M
of the unit servers
122
1
to
122
M
.
For example, in order for the first client
102
1
to reproduce video data, the communication system having the construction described above operates in the following manner. It is assumed that the first client
102
1
sends a request for video data for one second to the first unit server
122
1
. In response to the request, the file read-out section
112
1
delivers a file read-out command to the first file apparatus
111
1
. The first file apparatus
111
1
reads out relevant video data in response to the file read-out command and stores the video data once into the first buffer
113
1
. Then, the first distribution section
114
1
transmits the thus stored video data to the first client
102
1
via the network
103
.
The first client
102
1
reproduces the video data sent thereto while it sends a next read-out request to the next unit server
122
2
. In this manner, each of the clients
102
1
to
102
N
successively sends a request to the unit servers
122
1
to
122
M
to reproduce the video data which are continuous as a whole. The communication system which employs the server of the second prior art is advantageous in that the number of clients (
102
1
to
102
N
) can be increased using inexpensive file apparatus (
111
1
to
111
M
) or work stations.
By the way, the amount of video data is generally very large. Therefore, a hard disk is usually used for file storage apparatus. However, the hard disk employs mechanical operating members in order to read out data. Therefore, after a file read-out command is received, a waiting time such as a time for a seeking operation of a head and/or a latency time is required and object information cannot be read out immediately.
According to the communication system employing the server of the first prior art described hereinabove with reference to
FIG. 8
, in order to cover the waiting time, a buffer having a comparatively large capacity is used for the buffer
113
in the video server
101
. In particular, a comparatively large amount of video data including relevant video data is read out by a one time access to the file apparatus
111
such as a hard disk and is stored at a time into the buffer
113
having a comparatively large capacity. Then, when a request for video data following the relevant video data is received from the client
102
, the file apparatus
111
is not accessed, but the requested video data are transferred immediately from within the stored contents of the buffer
113
. Consequently, otherwise possible interruption of images on the client
102
side is prevented.
However, if the server of the second prior art described hereinabove with reference to
FIG. 9
is used in order to increase the number of clients, a considerably long time elapses before an access is received from the same client. It is assumed that the video server
121
includes, for example, totaling
100
first to one hundredth unit servers
122
1
to
122
100
. If it is assumed that each of the unit servers
122
1
to
122
100
transfers data for one second, then 100 seconds elapse before a certain one of the unit servers
122
1
to
122
100
is accessed for the next time from the same one of the clients
102
1
to
102
N
. Besides, if it is assumed that each one of the unit servers
122
1
to
122
100
supports, for example, 40 clients in average, then it requires a buffer having a capacity for 40 times 1,000 seconds. In this manner, the system which transfers video data without interruption to a desired client using the server of the second prior art is disadvantageous in that it requires a high cost.
SUMMARY OF THE INVENTION
It is an object of the present

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