Method for sending out absent messages from ISDN exchange system

A method for transferring absent messages between a first ISDN exchange system and a second ISDN exchange system, both being connected through respective digital trunk lines to a public telephone exchange system, and to respective digital telephones of a first and second extension each having a plurality of function keys, a LCD screen and a memory for storing a plurality of different absent messages, said method comprising the steps of:

• detecting whether the first extension of said first ISDN exchange system is set to an absent message sending mode when said first extension of said first ISDN exchange system is called up by the second extension of said second ISDN exchange system;
• retrieving a selected one of said plurality of different absent messages stored in a memory of said first ISDN exchange system when said first extension is set to said absent message sending mode;
• transmitting the retrieved absent message from said first ISDN exchange system through said digital trunk line to said public telephone exchange system;
• transmitting said retrieved absent message from said public telephone exchange system through said digital trunk line to said second ISDN exchange system;
• and
• displaying said retrieved absent message on LCD screen of said second extension's digital telephone, wherein said first ISDN exchange system transmits said retrieved absent message through the D channel of said digital trunk line to said public telephone exchange system to transmit said retrieved absent message through the D channel of said digital trunk line to said second ISDN exchange system.

A method, comprising:

• detecting when an incoming call is received from a telephone set of a calling party;
• detecting a mode of a telephone set of a called party;
• when said mode of the called party's telephone set corresponds to a message sending mode wherein a message is stored in a memory coupled to the called party's telephone set, detecting an exchange type corresponding to the incoming call, said message indicating that the called party is away from the called party's telephone set;
• when said exchange type corresponds to a public telephone exchange and a trunk line type of said public telephone exchange corresponds to a digital trunk line, retrieving said message from said memory and then transmitting said message through a D channel of said digital trunk line to the calling party's telephone set allowing said message to be displayed on a display panel of the calling party's telephone set;
• and
• when said exchange type corresponds to a private extension and the calling party's telephone set corresponds to a digital telephone set, retrieving said message from said memory and then transmitting said message through an extension line to the calling party's telephone set allowing said message to be displayed on a display panel of the calling party's telephone set.

A method, comprising:

• when a public telephone exchange subscriber utilizes a public telephone exchange system to call an extension subscriber of an ISDN exchange system, transmitting from the public telephone exchange system a call setup message to the ISDN exchange system, the public telephone exchange subscriber corresponding to a calling party and utilizing a calling party's telephone set, and the extension subscriber of the ISDN exchange system corresponding to a called party and utilizing a called party's telephone set;
• when the call setup message is received from the public telephone exchange system, transmitting from the ISDN exchange system a setup acknowledge message to the public telephone exchange system and sending ring signals from the ISDN exchange system to the called party's telephone set;
• transmitting an alert message only through a D channel of a digital line from the ISDN exchange system to the calling party's telephone set to advise the calling party that the called party is being signaled;
• and
• when a called-party-is-absent message is stored in a memory, said transmitting of said alert message includes said called-party-is-absent message retrieved from said memory, wherein said called-party-is-absent message indicates that the called party is away from the called party's telephone set.