1. Field of the Invention
The present invention relates to a data service system, data distribution unit, data terminal and data distribution method, suitably usable for a data service system for distributing digital data, for example.
2. Description of Related Art
Recently, the video and audio data compression technology and the digital signal processing technology in the fields of broadcasting and communications have shown remarkable innovations. In these situations, it has been proposed to organize between a user and server a data communications system incorporating such advanced data compression and signal processing technology. Generally, the data communications system is called "video on demand (VOD)" or "music on demand (MOD)" system and is designed to serve a digital data to a user accessing to the system.
In conventional data communication systems, however, the server adopts a data transfer mode to the server's own convenience with no consideration to the user's convenience. Thus, when a large volume of data is served to the user from the system, the reception of the large volume of data will take much time at the user's side even if the served data may not be of a high quality.
In the MOD system, a data requested by the user is sent from the server and down-loaded into a hard disk at the user's side. In this case, the user demanding for a data service will select a desired one of the received data according to a music guidance such as a music data list or a guide to artists or musicians and music titles and contents, and download it. Once the user requests the server for distribution of the desired music data, however, since a high-grade, high-quality data is sent from the server to the user though the user does not want so high a quality for the data, much time will be taken until the user finally gets the data and the user will be charged a lot for the service. This is a problem of the conventional MOD system.
Also with the VOD system, the user cannot select a quality for a video data the user wants to have from the server. For instance, there is a case that the user employs a small-screen monitor to reproduce the served video data because the data may not be of a high quality. In this case, however, since the server does not give any consideration to the user's convenience, the high quality of the served data cannot be covered by the user's small-screen monitor. This is a problem of the conventional VOD system.
As briefly mentioned above, the conventional data communication system does not reflect the user's request for the data transfer mode. The data served to the user from the server is of a higher a quality than the user hopes, and the long time required for the data downloading will cause the data communications network to be congested when many users access the system. Thus, some of the data served from the system imposes a big fee and a long download time on the user. For these reasons, the users avoids downloading the served data into his player.