Key telephone system without common control

• US 6,088,362 A
• Filed: 05/26/1998
• Issued: 07/11/2000
• Est. Priority Date: 12/28/1995
• Status: Expired due to Term

• Current Assignee: Avaya Incorporated
• Original Assignee: Nortel Networks Corporation
• Inventors: Turnbull, Robert, Lucas, Michael J., McKinney, Brian, Eyre, Alan D., Westergaard, David, Yee, Bruce W.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): HOM, SHICK C
• Application Number:
  US09/084,167
• Time in Patent Office: 777 Days
• Field of Search: 370/212, 370/276, 370/278, 370/294, 370/442, 370/508, 370/512, 370/509, 375/222, 375/354, 375/357, 375/358, 375/359, 375/367, 375/220, 340/286.06, 340/286.07, 340/286.08, 340/286.09, 379/93.11, 379/230
• US Class Current: 370/442
• CPC Class Codes: H04L 5/1492 with time compression, e.g. operating according to the ping-pong technique
• CPC Class Codes: H04M 9/002 with subscriber controlled access to a line, i.e. key telephone systems

Abstract

A multi-line key telephone system not having a key service unit includes three analog telephone lines to which up to eight, three-line telephones may be connected to provide enhanced service features with cost-effectiveness. System reliability is maintained, notwithstanding a power dependency of the telephones, by including POTS telephones to provide uninterrupted essential telephone service in the event of a power outage. Both data and voice communications between two or more of the three-line telephones is achieved by converting an input digital bit stream from either a digital or analog source into a corresponding out-of-band binary FSK radio frequency output signal that is transceivingly communicated between the three-line telephones as data packets within a TDM frame. The out-of-band signal thus permits analog voice communications on the same line to proceed without interference. A telephone initiating a communications session acts as a master station, establishing inter-station communications synchronous at the frame level and asynchronous at the packet level. The called telephone functions as a slave station in a second time slot synchronized to a first time slot in the TDM frame received from the master. Temporary storage of data in firmware buffers and controlled timing at both the master and slave permits these stations to function within their respective TDM frame time slots.

Claims

1. A method for selectively effecting data and voice packet transfers and communicating time division multiplex protocol control between a pair of at least two telephone stations connected across and competing for seizure of a two-wire telephone line, comprising the combined steps of:

arbitrating seizure of the line to set one of the competing telephone stations as a communications session master preparatory to calling one of the other competing telephone stations designated as slave stations;

transmitting an out-of-band data signal including a data packet having a valid header and start bit from the master station to acquire inter-station synchronization at a TDM frame level with a directly called slave station;

generating a synchronizing pulse in response to receiving the valid header and start bit at a receiver of the called slave station; and

adjusting a master time clock in the called slave station to conform to the timing of the master station by defining the respective positions of subsequently received voice and data packets within a received TDM frame having a predetermined data bit structure.

2. The method as claimed in claim 1, comprising the further steps of:

enabling a voice channel of the master station for packetizing a plurality of voice bytes received from a digital signal processor and accumulated in a transmit buffer of the master station; and

transmitting individual ones of the voice packets at a packet level to the called slave station in step with a transmit enable pulse from a master station synchronizer that defines the correct voice time slot within the TDM frame.

3. The method as claimed in claim 2, comprising the further steps of:

enabling a voice channel of the called slave station to maintain synchronization with the voice channel of the master station;

disabling the data channel of the master station;

coupling a plurality of voice bytes received from the master station to a receive voice buffer in the called slave station for accumulation and temporary storage therein; and

transferring the stored voice bytes to a digital signal processor at the called slave station for subsequent processing.

4. The method as claimed in claim 3, comprising the further steps of:

generating and buffering digitized voice data at the calling and called stations in each direction for transmit and receive functions to accommodate inter-station communications synchronous at the frame level and asynchronous at the packet level;

enabling a data transmit mode in the called slave station to seize the line, packetize the digitized voice data and transmit an out-of-band data packet to the master station during the second time slot of the TDM frame in response to the master station call; and

receiving the data packet at the master station during the first time slot of the TDM frame.

5. A method for establishing full-duplex intercom communications with signaling between a pair of at least two telephone stations connected across and competing for seizure of a two-wire transmission line carrying an analog voiceband call, comprising the combined steps of:

arbitrating seizure of the line to set one of the competing telephone stations as a communications session master preparatory to calling one of the other competing telephone stations designated as slave stations;

transmitting an out-of-band data signal from the master station to a directly called slave station during a first time slot of a TDM frame to establish master station priority therebetween preparatory to initiating an intercom session;

signaling the called slave station to establish its status as a slave station assigned to a second time slot of the TDM frame synchronized to the first time slot of the master station to effect inter-station frame synchronization;

generating and buffering digitized voice data at the calling and called stations in each direction for transmit and receive functions to accommodate inter-station communications synchronous at a frame level and asynchronous at a packet level;

enabling a data transmit mode in the called slave station to seize the line, packetize the digitized voice data and transmit an out-of-band data packet to the master station during the second time slot of the TDM frame in response to the master station call; and

receiving the data packet at the master station during the first time slot of the TDM frame.

6. The method as claimed in claim 5, comprising the further step of, monitoring the line at a calling station following a predetermined delay after dispatching the last byte of an eight byte data packet to ascertain seizure of the line by the called station, thereby acquiring a noise-free line for listening.

7. Apparatus for selectively effecting data and voice packet transfers and communicating time division multiplex protocol control between a pair of at least two telephone stations connected across and competing for seizure of two-wire telephone line, comprising in combination:

means for arbitrating seizure of the line to set one of the competing telephone stations as a communications session master preparatory to calling one of the other competing telephone stations designated as slave stations;

means for transmitting an out-of-band data signal including a data packet having a valid header and start bit from the master station to acquire inter-station synchronization at a TDM frame level with a directly called slave station;

means for generating a synchronizing pulse in response to receiving the valid header and start bit at a receiver of the called slave station; and

means for adjusting a master time clock in the called slave station to conform to the timing of the master station by defining the respective positions of subsequently received voice and data packets within a received TDM frame having a predetermined data bit structure.

8. Apparatus for establishing full-duplex intercom communications with signaling between a pair of at least two telephone stations connected across and competing for seizure of a two-wire transmission line carrying an analog voiceband call, comprising in combination:

means for arbitrating seizure of the line to set one of the competing telephone stations as a communications session master preparatory to calling one of the other competing telephone stations designated as slave stations;

means for transmitting an out-of-band data signal from the master station to a directly called slave station during a first time slot of a TDM frame to establish master station priority therebetween preparatory to initiating an intercom session;

means for signaling the called slave station to establish its status as a slave station assigned to a second time slot of the TDM frame synchronized to the first time slot of the master station to effect inter-station frame synchronization;

means for generating and buffering digitized voice data at the calling and called stations in each direction for transmit and receive functions to accommodate inter-station communications synchronous at a frame level and asynchronous at a packet level;

means for enabling a data transmit mode in the called slave station to seize the line, packetize the digitized voice data and transmit an out-of-band data packet to the master station during the second time slot of the TDM frame in response to the master station call; and

means for receiving the data packet at the master station during the first time slot of the TDM frame.