(i) Field of the Invention
The present invention relates to a voice mail system, particularly to a voice mail system in which terminals are connected via a radio communication network to a server.
(ii) Description of the Related Art
Recently, in a local area network (LAN) or a wide area network (WAN) which is constituted of terminals and a server connected to a network, text electronic mails exchanged between the terminals via the server have been prevailing. Moreover, a document preparation system has been proposed in which the increasing number of electronic mails are efficiently edited and displayed on a display device.
For example, Japanese Patent Application Laid-open No. 245352/1989 discloses a document preparation system which is provided with a server for classifying document preparation data for each terminal and accumulating the data in a storage area to effectively use a kanji dictionary or another resource usable in common and terminals each having a function of reading and editing the data accumulated in the storage area of the server. Moreover, Japanese Patent Application Laid-open No. 240748/1990 discloses an information processing device in which so as to effectively use a data accumulation resource, information data is managed in one way by a server so that the information data in the server can be edited by plural terminals. Furthermore, a data compression system or the like has been recently put to practical use in which a data accumulation resource, a communication resource and the like are effectively used by decreasing redundancy of information data.
In a conventional text electronic mail system, in a case where comments on a received mail are returned or transferred, the comments are attached as reference data partially or entirely to the received mail and returned or transferred.
However, when the returning/transferring is performed by using a radio communication which is generally narrower in communication band and more expensive as compared with a cable communication, the quantity of the applied reference data has an influence on communication cost, but there is only a small necessity to intentionally reduce the applied quantity of the reference data for the saving of the communication cost because the quantity of the text information is small.
Here, it is supposed that the returning/transferring is performed in a voice mail system in which plural terminals are connected via a radio communication network or the like to a server. It is clear that in order to answer or indicate a complicated message, the reference to a received voice is more important rather than the reference to the text document mail. However, even if the quantity of voice data sufficient for providing a meaning as a reference voice is compressed with a compression technique, the quantity of data to be transmitted is remarkably large. This means that the application of the reference data to the communication resource is a large burden on the communication cost in the voice mail system as compared with the text electronic mail system in which comments can be easily attached or inserted to the received text mail and sent. It is especially a large burden in the voice mail system using the radio communication which is largely restricted as the communication resource. This suggests that there should be a similar problem about family data, image data or another information which needs to form a mass of data with a certain size to have a meaning.
Furthermore, in the conventional voice mail system, a voice mail can be transmitted only in one direction, and a bi-directional voice mail cannot be transmitted/received among plural terminals.