In recent years, with the spread of a broadband network, necessity of services is increasing that allow viewing of wanted images when wanted. These services can be realized by delivering contents such as an image to a terminal via a network. As a technology which realizes such services, there exists an image contents delivery system. This system installs an image delivery server in which image contents are accumulated in advance in a network, for example, and delivers image contents from the image delivery server according to a delivery request from a user terminal.
Also, as a contents delivery system similar to the image contents delivery system mentioned above, there exits a web system in which a web delivery server delivers web contents (home page, text data and so on) to a user terminal of delivery request source.
In this web system, when requests of information delivery concentrate on a web delivery server, the web delivery server cannot process the requests by processing power of the web delivery server any more. Therefore, a user terminal may be made to wait a long time for information delivery. Or, in such a case, a failure may occur in which the user terminal cannot receive delivery at all.
Therefore, a delivery server with which a large number of receiving terminals are connected requires construction of a system which balances or reduces a load of the delivery server, and can continue information delivery stably.
Here, as a means to solve load concentration of a delivery server, a method which utilizes a load balancer in a network in which a client (receiving terminal) and a delivery server transmit and receive data is generally used.
For example, Japanese Patent Application Laid-Open No. 2003-242057 (hereinafter, referred to as patent document 1) discloses a contents delivery system using a load balancer. In the contents delivery system described in this patent document 1, a plurality of web delivery servers which can deliver same web contents and a load balancer are installed. The load balancer receives registration of an IP address of respective web delivery servers and also receives setting of one IP address for the load balancer itself. The IP address of the load balancer is disclosed to a receiving terminal as a client as an address of a web delivery server which delivers web contents.
Also, the load balancer always collects load status of the web delivery servers and grasps free web delivery servers with enough room of processing power.
On the other hand, the receiving terminal regards the load balancer as a web delivery server and transmits a delivery request.
The load balancer transmits the received delivery request to a free web server. Then, the free web delivery server outputs a processing result to the delivery request to the load balancer. The load balancer outputs the received processing result to the receiving terminal which is the delivery source of the request.
A contents delivery system with such a structure includes a plurality of web delivery servers. A load balancer manages these web delivery servers and further performs transmission or reception of data. By this structure, even if access concentrates in the contents delivery system, a load of web delivery servers is balanced.
However, in case of an image delivery server, it is difficult to utilize the load balancer mentioned above. In case of delivery of small data such as text data, because processing in which the load balancer transmits delivery data to the receiving terminal is completed in a short time, quantity of computational resources which is needed for transmission processing is little. However, in case of image delivery, image data which an image delivery server transmits is huge. Moreover, the load balancer has to keep transmitting image data to the receiving terminal continually. For this reason, transmission processing consumes computational resources and so on of the load balancer in large quantities, and as a result, the load of the load balancer itself becomes high. This is the reason why it is difficult to utilize the load balancer mentioned above in case of an image delivery server.
Also, in case a number of connections of receiving terminals is large, and when a load balancer is used, the load balancer will become a bottleneck and the image delivery server cannot deliver an image stably any more. By the way, in case such as the contents delivery system mentioned above delivers image data such as program contents, for example, volume of data which constitutes the image is extremely large compared with text data and so on which a web delivery server and so on delivers. Also, the contents delivery system needs to keep delivering the data continually.
Therefore, delivery processing of an image uses CPU (Central Processing Unit; central processing unit) of the delivery server for a long time. Also, the delivery processing of an image consumes computational resources such as a network band in large quantities. Accordingly, the load of the image delivery server which delivers image data is easy to become high.
Accordingly, when an image delivery server is structured, a technology of load balancing of the image delivery server becomes more important.
Accordingly, as a technology of load balancing of an image delivery server, utilization of not a load balancer but a media director can be considered. As an example of a media director, there is a contents delivery system described in Japanese Patent Application Laid-Open No. 2005-332373 (hereinafter, referred to as patent document 2). The contents delivery system described in patent document 2 includes one media director and a plurality of media engines. The contents delivery system with such a structure operates as follows.
The respective media engines include a memory unit for media contents. Also, the respective media engines include a communication channel for taking out media contents via a network. Also, the respective media engines include a communication channel for streaming media contents via a network. The media director directs extraction of media contents through the network by a selected media engine. Also, the media director includes a controller which fits to trace contents stored in a media engine. This controller fits with redirecting contents which are requested from a media console connected to a media station to one selected media engine among media engines which stores contents corresponding to a streaming request.
However, when a scale becomes large, by the same reason as in the case of a load balancer, an image delivery service will also become difficult to utilize the media director like the contents delivery system described in patent document 2.
From such reasons, an image delivery service needs a means which controls to balance a load of the image delivery service and to reduce a load of a delivery server without using a load balancer or a media director
Accordingly, as a contents delivery system which balances a load of an image delivery service without utilizing a load balancer or a media director, a contents delivery system described in Japanese Patent Application Laid-Open No. 2006-113735 (hereinafter, referred to as patent document 3) is proposed. This contents delivery system transmits to a receiving terminal, as delivery data which a contents delivery server delivers, one which are contents data added with an identifier of the contents data and status of a load of the server. The receiving terminal determines the load status of the contents delivery server, connects with other contents delivery server with light load, and continues reception of the contents data.
Also a load balancing system described in Japanese Patent Application Laid-Open No. 2008-71156 (hereinafter, patent document 4) includes a means to exchange load information among a plurality of servers. In this invention, by exchanging this load information, flexibility of processing is accomplished such as when a load of own server exceeds a load target value, making other server execute processing.