Electrical computers and digital processing systems: multicomput – Computer network managing – Network resource allocating
Reexamination Certificate
2000-10-20
2004-07-06
Burgess, Glenton B. (Department: 2153)
Electrical computers and digital processing systems: multicomput
Computer network managing
Network resource allocating
C709S229000, C709S219000, C709S203000, C709S223000, C709S231000, C725S115000, C725S119000, C714S004110
Reexamination Certificate
active
06760765
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to cluster server apparatuses, and more specifically, to a cluster server apparatus for distributing streaming data such as video data in response to requests from a plurality of terminals connected to the cluster server apparatus through a network.
2. Description of the Background Art
For cluster server apparatuses that distribute streaming data typified by video data, continuous distribution of the streaming data to terminals connected to the cluster server apparatuses through a network is required. Since the volume of the streaming data is generally enormous, a storage device such as a large-capacity hard disk is used for data storage in the cluster server apparatus.
However, in the cluster server apparatus structured by a server comprising a large-capacity storage device for data storage, the number of terminals for receiving data is restricted by the capability limitations of the server. Therefore, in one conventional method for distribution of streaming data to a plurality of terminals, a plurality of servers are provided in the cluster server apparatus, and requests from the terminals are distributed in rotation among the plurality of servers.
An example of the structure of a conventional cluster server apparatus using the above-described method of distributing requests in rotation among the plurality of servers is briefly described below.
FIG. 18
is a block diagram showing an example of the structure of a distribution system using the above-described conventional cluster server apparatus.
As shown in
FIG. 18
, m terminals
40
1
to
40
m
(where m is an integer not less than 2) and a cluster server apparatus
200
are connected together via a network
501
in the conventional distribution system. The cluster server apparatus
200
is structured by n cache servers
20
1
to
20
n
(where n is an integer not less than 2) and a content server
300
. The cache servers
20
1
to
20
n
are each connected to the content server
300
via an internal network
503
.
The cache servers
20
1
to
20
n
include receivers
21
1
to
21
n
, caches
22
1
to
22
n
, and distribution units
23
1
to
23
n
, respectively. The content server
300
includes a streaming data storage unit
301
, a read unit
302
, a cache
303
, and a distribution unit
304
. Stream data is stored in the streaming data storage unit
301
as packets, where packets are a unit of the streaming data.
Now assume that the terminal
40
1
requests the content server
300
for certain streaming data. In response to the request, the read unit
302
issues a read request for the streaming data to the streaming data storage unit
301
in the content server
300
. The streaming data, in response to the read request, is then read in the read unit
302
. The read streaming data is cached in the cache
303
. The distribution unit
304
sends the streaming data which is cached in the cache
303
to the cash server
20
1
. In the cash server
20
1
, the receiver
21
1
receives the streaming data sent from the content server
300
. The received streaming data is cached in the cache
22
1
of the cache server
20
1
. The distribution unit
23
1
sends the streaming data cached in the cache
22
1
to the terminal
40
1
.
Next, when the terminal
40
2
requests the content server
300
for certain streaming data, the cluster server apparatus
200
uses the cache server
20
2
, and when the terminal
40
3
requests the content server
300
for certain streaming data, the cluster server apparatus
20
uses the cache server
20
3
. In this way, the cluster server apparatus
200
uses the cache servers in rotation as the cluster server apparatus
200
receives multiple requests from the terminals.
As stated above, in the conventional cluster server apparatus
200
, the cache servers
20
1
to
20
n
are structured in parallel for cyclical use in handling requests. With this structure, the number of terminals
40
1
to
40
m
for receiving streaming data is increased in the entire system.
In addition to the above, another conventional cluster server apparatus which caries out a data recovery after recovery from a failure which occurred in one server in the cluster server apparatus has been disclosed in Japanese Patent Laid-Open Publication No. 8-263351 (1996-263351). In the conventional cluster server apparatus disclosed in this publication, each cache server caches on updating history of the content server. After failure recovery, the latest updating history cached in the cache server is used for data recovery in the content server. Therefore, even if a failure occurs in the data of the content server, data recovery can be quickly carried out in this conventional cluster server apparatus without requiring system suspension.
However, in the conventional cluster server apparatus
200
, requests from the terminals
40
1
to
40
m
are provided to the cache servers
20
1
to
20
n
simply in rotation. Therefore, if streaming data that is continuous in time such as video data is to be distributed, loads on the cache servers
20
1
to
20
n
are not properly distributed, and thereby continuous video images may be interrupted.
Further, if a failure occurs in the cache server during streaming data distribution, another server has to distribute the streaming data from the start of the streaming data instead of the portion of the streaming data which remains to be transmitted when the failure occurred.
Still further, in the conventional cluster server apparatus disclosed in the above publication, the updating history of the content server is held only by the cache servers. Therefore, if any failure occurs in the cache servers, the service to the terminals is thereby interrupted.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a cluster server apparatus for optimally distributing, in response to requests from terminals, loads on cache servers while continuing, even if a failure occurs in any one of the cache servers, data distribution to the terminals without any problem (frame skip) and for recovering from the failure.
The present invention has the following features to achieve the object above.
The present invention is directed to a cluster server apparatus for distributing streaming data such as moving-picture data continuously in time in response to requests from a plurality of terminals connected to the cluster server apparatus through a network.
First, in order to achieve load-distribution among cache servers, the present invention comprises a plurality of cache servers which are each operable to distribute the streaming data corresponding to the requests from the terminals, and a load-distribution server which is operable to receive the request from one of the terminals and to transfer the request to one of the plurality of cache servers based on whether streaming data that corresponds to the request is stored in the cache servers or not and the state of the distribution of streaming data by the cache servers, and a content server with a streaming data storage unit which is operable to store the streaming data, where the content server is operable to send, to the cache server, the streaming data that corresponds to the request from the cache server. Each of the cache servers comprises a streaming data storage unit which is operable to store the streaming data from the content server, and a request transfer unit which is operable to receive the request transferred from the load-distribution server. If the streaming data which corresponds to the request is stored in the streaming data storage unit, the request transfer unit is operable to output an instruction for distributing the stored streaming data. If, however, the streaming data which corresponds to the request is not stored the streaming data storage unit, the request transfer unit is operable to transfer the request to the content server, to store the streaming data from the content server in the steaming data storage unit, and to output an instruction for
Asai Rieko
Horiuchi Masaki
Omura Takeshi
Burgess Glenton B.
Edelman Bradley
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