DIGITAL COMMUNICATIONS SYSTEM

• US 3,851,104 A
• Filed: 04/11/1973
• Issued: 11/26/1974
• Est. Priority Date: 04/11/1973
• Status: Expired due to Term

• Current Assignee: David G. Willard, John W. Shay, Maurice G. Vacherot, Michael S. Cogan
• Original Assignee: David G. Willard, John W. Shay, Maurice G. Vacherot, Michael S. Cogan
• Inventors: Willard, David G., Cogan, Michael S., Vacherot, Maurice G., Shay, John W.
• Primary Examiner(s): Blakeslee, Ralph D.
• Application Number:
  US05/350,043
• Time in Patent Office: 594 Days
• Field of Search: 179/15BA,15BU,15BW,15BY
• US Class Current: 370/442
• CPC Class Codes: H04L 12/4035 in which slots of a TDMA packet structure are assigned based on a contention resolution carried out at a master unit TDM/TDMA multiplex systems per se H04J3/1694; hybrid switching systems H04L12/64

Abstract

A time division multiple access communications system which provides communication linkages between remote subscriber terminals. The communications system comprises a plurality of remote terminals interconnected by a common wideband signal path and a central control terminal. A repetitive framed message signal format is maintained by the control terminal to provide a predetermined average time required for access to the signal path for each remote terminal. Communication links over the channel between remote terminals are further provided, wherein the links comprise adaptively allocated portions of the channel spectrum in response to request signals from the various remote terminals.

Claims

1. A time division multiple access digital communications system for providing a communication link over a common signal path between at least two remote terminals, said system having a plurality of multiple bit digital message signals, each of said signals being disposed in a one of a plurality of time slots in a repetitive framed time sequence, comprising:

a. a common signal path, b. a plurality of remote subscriber terminals connected c. to said common signal path, and d. a central control terminal connected to said path having means for allocating predetermined numbers of time slots to selected ones of said remote terminals during each of said framed sequences, said predetermined number of slots being for transmission of digital sign-on request signals by the respective ones of said selected terminals to direct said central control terminal to link the requesting remote terminal to said signal path, said predetermined number of slots for providing said control terminal to be responsive to said signon request signals of the respective ones of said selected terminals during a predetermined proportion of each of said framed sequences, whereby said allocation of said predetermined number of time slots provides the respective ones of said remote terminals with a predetermined mean time for access to said signal path.

2. A time division multiple access digital communications system as described in claim 1 wherein each of said remote terminals includes:

a service request means for transmitting a digital sign-on request signal on said path to request a communication link, said link having a requested data rate, and wherein said central control terminal includes;

means for receiving from requesting remote terminals said transmitted sign-on request signals and for allocating to the respective ones of said requesting terminals a selected number of time slots during Each of said framed sequences to form a communication link between the ones of said requesting terminals and other terminals connected to said path, said selected number of slots for the respective ones of said requesting remote terminals being determined in response to said requested data rate, whereby the information capacity of said signal path is allocated to the respective ones of said requesting remote terminals in accordance with the various sign-on request signals.

3. A time division multiple access digital communication system as described in claim 2 wherein each of said remote terminals includes:

a sign-off request means for transmitting a digital sign-off request signal on said path to request the termination of said established communication link, and wherein said central control terminal includes;

means for receiving from requesting remote terminals said transmitted sign-off request signals and for disassociating said selected number of time slots previously allocated to the respective ones of said requesting terminals to terminate said communication link between ones of said requesting terminals and other terminals connected to said path, whereby the previously allocated portions of the information capacity of said signal path is available to be reallOcated to the respective one of said requesting remote terminals in accordance with the various sign-on request signals.

4. A time division multiple access digital communications system as defined in claim 3 wherein said central control terminal includes:

means for identifying a subset of time slots from a set having 2n sequentially numbered time slots in a repetitive framed time sequence;

where n is an integer, said subset of slots being uniquely defined by a reference slot number, fsn, which is representative of a numbered member of said subset in said framed sequence, and a slot spacing number, m, where m is an integer less than or equal to n and is representative of the spacing between members of said subset in said framed sequence, said spacing being equal to 2m slots, said identifying means comprising a. means for generating a binary coded digital fsn signal representative of said reference slot number, fsn. b. a reference means for identifying the various ones of said set of 2n sequentially numbered time slots in said repetitive framed time sequence, and for generating a sequential binary coded reference signal associated with each of the successively identified time slots, c. means for comparing the m least significant bits of said successively generated reference signals with the m least significant bits of said digital fsn signal representative of said reference slot number, fsn, d. means for generating a control signal when said m least significant bits of said compared signals exactly match, and for generating no such control signal otherwise, said control signal being coincident with and identifying the members of said subset of time slots.

5. A time division multiple access digital communications system as defined in claim 4 wherein said common signal path includes at least one pair of communication channels, the first channel of said pair for transmission of digital signals directed away from said control terminal, and the second of said pair for transmission of digital signals directed toward said control terminal, wherein each of said remote subscriber terminals has an associated binary address word for identification, and wherein said central control terminal further includes:

a. means for generating and transmitting a digital frame synchronization signal on said first channel in predetermined ones of said time slots, said signal having a binary code word for synchronizing the operation of said remote terminals, b. means for generating and transmitting a digital request slot assignment signal on said first channel in predetermined ones of saId time slots, said signal comprising a one of said remote terminal address words and at least one word for assigning to said addressed terminal a set of time slots in a frame to be request slots, said word for defining a first time slot and spacing for a plurality of subsequent time slots in a frame, said request slots being assigned to the correspondingly addressed remote terminal for the transmission of digital sign-on request signals, c. means for receiving a digital sign-on request signal on said second channel from a requesting remote terminal in a one of said associated assigned request slots, said sign-on request signal comprising said requesting remote terminal address word, an intended receiver remote terminal address word and a data rate request word, said sign-on request signal for requesting said control terminal to link said requesting remote terminal via said signal path with a data rate corresponding to said rate request word, d. means for generating and transmitting a digital sign-on response signal on said first channel in a one of said request slots for assigning a set of data slots to said requesting terminal for data transmission, said sign-on response signal comprising said requesting terminal address word, said intended receiver terminal address word and at least one word for identifying a set of data slots, said word for defining a first data slot and spacing for a plurality of subsequent data slots in a frame assigned to said first remote terminal for data transmission, the number of data slots in said set corresponding to the number defined by said data rate request word, e. means for receiving digital data signals on said second channel in ones of said data slots assigned to the respective ones of said remote terminals, said data signals comprising a remote terminal address word and a data word, and f. means for transmitting said received digital data signals on said first channel in ones of said data slots assigned to the respective ones of said remote terminals, said data signals comprising a remote terminal address word and a data word, g. means for receiving a digital sign-off request signal on said second channel from a requesting remote terminal in a one of said associated assigned request slots, said sign-off request signal comprising said requesting remote terminal address word, an intended receiver remote terminal address word, and a sign-off indicator word, said sign-off request signal for requesting said control terminal to disassociate said requesting remote terminal from said signal path, h. means for generating and transmitting a digital sign-off response signal on said first channel in a one of said request slots for indicating to said requesting terminal that the previously established communication link is terminated, said sign-off response comprising said requesting terminal address word, said intended receiver terminal address word and said sign-off indicator word.

6. A time division multiple access digital communications system as defined in claim 5 wherein each of said remote subscriber terminals includes:

a. means for receiving said digital frame synchronization signals on said first channel in a one of said time slots, b. means for identifying and selectively receiving the respective ones of said digital request slot assignment signals on said first channel, said selectively received signals having the terminal address word associated with said receiving terminal, c. means for generating and transmitting a one of said digital sign-on request signals on said second channel in a one of said assigned request slots for the respective ones of said terminals, d. means for identifying and selectively receiving the respective ones of said digital sign-on response signals in ones of said time slots on said first channel, said selectively received signals having the terminal address word associated with said receiving terminal, e. means for generating and transmitting said digital data signals on said second channel in a one of said assigned data slots for the respective ones of said terminals, and f. means for identifying and selectively receiving the respective ones of said digital data signals in said time slots on said first channel, said selectively received signals having the terminal address word associated with said receiving terminal. g. means for generating and transmitting said digital sign-off request signal on said second channel in a one of said assigned request slots for the respective ones of said terminals, and h. means for identifying and selectively receiving the respective ones of said digital sign-off response signals on said first channel, said selectively received signals having the terminal address word associated with said receiving terminal.

7. A time division multiple access digital communications system as defined in claim 3 wherein said common signal path includes at least one pair of communication channels, the first channel of said pair for transmission of digital signals directed away from said control terminal, and the second of said pair for transmission of digital signals directed toward said control terminal, wherein each of said remote subscriber terminals has an associated binary address word for identification, and wherein said central control terminal further includes:

a. means for generating and transmitting a digital frame synchronization signal on said first channel in predetermined ones of said time slots, said signal having a binary code word for synchronizing the operation of said remote terminals, b. means for generating and transmitting a digital request slot assignment signal on said first channel in predetermined ones of said time slots, said signal comprising a one of said remote terminal address words and at least one word for assigning to said addressed terminal a set of time slots in a frame to be request slots, said word for defining a first time slot and spacing for a plurality of subsequent time slots in a frame, said request slots being assinged to the correspondingly addressed remote terminal for the transmission of digital sign-on request signals, c. means for receiving a digital sign-on request signal on said second channel from a requesting remote terminal in a one of said associated assigned request slots, said sign-on request signal comprising said requesting remote terminal address word, an intended receiver remote terminal address word and a data rate request word, said sign-on request signal for requesting said control terminal to link said requesting remote terminal via said signal path with a data rate corresponding to said rate request word, d. means for generating and transmitting a digital sign-on response signal on said first channel in a one of said request slots for assigning a set of data slots to said requesting terminal for data transmission, said sign-on response signal comprising said requesting terminal address word, said intended receiver terminal address word and at least one word for identifying a set of data slots, said word for defining a first data slot and spacing for a plurality of subsequent data slots in a frame assigned to said first remote terminal for data transmission, the number of data slots in said set corresponding to the number defined by said data rate request word, e. means for receiving digital data signals on said second channel in ones of said data slots assigned to the respective ones of said remote terminals, said data signals comprising a remote terminal address word and a data word, and f. means for transmitting said received digital data signals on said first channel in ones of said data slots assigned to the respective ones of said remote terminals, said data signals comprising a remote terminal address word and a data word. g. means for receiving a digital sign-off request signal on said second channel from a requesting remote terminal in a one of said associated assigned request slots, said sIgn-off request signal comprising said requesting remote terminal address word, an intended receiver remote terminal address word, and a sign-off indicator word, said sign-off request signal for requesting said control terminal to disassociate said requesting remote terminal from said signal path, h. means for generating and transmitting a digital sign-off response signal on said first channel in a one of said request slots for indicating to said requesting terminal that the previously established communication link is terminated, said sign-off response comprising said requesting terminal address word, said intended receiver terminal address word and said sign-off indicator word.

8. A time division multiple access digital communications system as defined in claim 7 wherein each of said remote subscriber terminals includes:

a. means for receiving said digital frame synchronization signals on said first channel in a one of said time slots, b. means for identifying and selectively receiving the respective ones of said digital request slot assignment signals on said first channel, said selectively received signals having the terminal address word associated with said receiving terminal, c. means for generating and transmitting a one of said digital sign-on request signals on said second channel in a one of said assigned request slots for the respective ones of said terminals, d. means for identifying and selectively receiving the respective ones of said digital sign-on response signals in ones of said time slots on said first channel, said selectively received signals having the terminal address word associated with said receiving terminal, e. means for generating and transmitting said digital data signals on said second channel in a one of said assigned data slots for the respective ones of said terminals, and f. means for identifying and selectively receiving the respective ones of said digital data signals in said time slots on said first channel, said selectively received signals having the terminal address word associated with said receiving terminal. g. means for generating and transmitting said digital sign-off request signal on said second channel in a one of said assigned request slots for the respective ones of said terminals, and h. means for identifying and selectively receiving the respective ones of said digital sign-off response signals on said first channel, said selectively received signals having the terminal address word associated with said receiving terminal.

9. A time division multiple access digital communications system for providing a communication link over a common signal path between two or more of remote terminals, said system having a plurality of multiple bit digital message signals, each of said signals being disposed in a one of a plurality of time slots in a repetitive framed time sequence, comprising:

a. a common signal path, b. a plurality of remote subscriber terminals connected to said common signal path, c. a service request means in each of said remote terminals for transmitting a digital sign-on request signal on said path to request a communication link, said link having a requested data rate, and a central control terminal connected to said path for receiving from requesting terminals said transmitted sign-on request signals, and for allocating to the respective ones of said requesting terminals a selected number of time slots during each of said framed sequences to form a communication link between the ones of said requesting terminals and other terminals connected to said path, said selected number of slots for the respective ones of said requesting remote terminals being determined in response to said requested data rate, whereby the information capacity of said signal path is allocated to the respective ones of said requesting remote terminals in accordance with the various sign-on request signals.

10. A time division multiple access digital communication systEm as described in claim 9 wherein each of said remote terminals includes:

a sign-off request means for transmitting a digital sign-off request signal on said path to request the termination of said established communication link, and wherein said central control terminal includes;

means for receiving from requesting remote terminals said transmitted sign-off request signals and for disassociating said selected number of time slots previously allocated to the respective ones of said requesting terminals to terminate said communication link between ones of said requesting terminals and other terminals connected to said path, whereby the previously allocated portions of the information capacity of said signal path is available to be reallocated to the respective one of said requesting remote terminals in accordance with the various sign-on request signals.

11. A time division multiple access digital communications system as defined in claim 10 wherein said central control terminal includes:

means for identifying a subset of time slots from a set having 2n sequentially numbered time slots in a repetitive framed time sequence, where n is an integer, said subset of slots being uniquely defined by a reference slot number, fsn, which is representative of a numbered member of said subset in said framed sequence, and a slot spacing number, m, where m is an integer less than or equal to n and is representative of the spacing between members of said subset in said framed sequence, said spacing being equal to 2m slots, said identifying means comprising;

a. means for generating a binary coded digital fsn signal representative of said reference slot number, fsn, b. a reference means for identifying the various ones of said set of 2n sequentially numbered time slots in a repetitive framed time sequence, and for generating said sequential binary coded reference signal associated with each of the successively identified time slots, c. means for comparing the m least significant bits of said successively generated reference signals with the m least significant bits of said digital fsn signal representative of said reference slot number, fsn, d. means for generating a control signal when said m least significant bits of said compared signals exactly match, and for generating no such control signal otherwise, said control signal being coincident with and identifying the members of said subset of time slots.

12. A time division multiple access digital communications system as defined in claim 11 wherein said common signal path includes at least one pair communication channels, the first channel of said pair for transmission of digital signals directed away from said control terminal, and the second of said pair for transmission of digital signals directed toward said control terminal, wherein each of said remote subscriber terminals has an associated binary address word for identification, and wherein said central control terminal further includes:

a. means for generating and transmitting a digital frame synchronization signal on said first channel in predetermined ones of said time slots, said signal having a binary code word for synchronizing the operation of said remote terminals, b. means for generating and transmitting a digital request slot assignment signal on said first channel in predetermined ones of said time slots, said signal comprising a one of said remote terminal address words and at least one word for assigning to said addressed terminal a set of time slots in a frame to be request slots, said word for defining a first time slot and spacing for a plurality subsequent time slots in a frame, said request slot being assigned to the correspondingly addressed remote terminal for the transmission of digital sign-on request signals, c. means for receiving a digital sign-on request signal on said second channel from a requestinG remote terminal in a one of said associated assigned request slots, said sign-on request signal comprising said requesting remote terminal address word, an intended receiver remote terminal address word and a data rate request word, said sign-on request signal for requesting said control terminal to link said requesting remote terminal via said signal path with a data rate corresponding to said rate request word, d. means for generating and transmitting a digital sign-on response signal on said first channel in a one of said request slots for assigning a set of data slots to said requesting terminal for data transmission said sign-on response signal comprising said requesting terminal address word, said intended receiver terminal address word and at least one word for identifying a set of data slots, said word for defining a first data slot and spacing for a plurality of subsequent data slots in a frame assigned to said first remote terminal for data transmission, the number of data slots in said set corresponding to the number defined by said data rate request word, e. means for receiving digital data signals on said second channel in ones of said data slots assigned to the respective ones of said remote terminals, said data signals comprising a remote terminal address word and a data word, and f. means for transmitting said received digital data signals on said first channel in ones of said data slots assigned to the respective ones of said remote terminals, said data signals comprising a remote terminal address word and a data word;

g. means for receiving a digital sign-off request signal on said second channel from a requesting remote terminal in a one of said associated assigned request slots, said sign-off request signal comprising said requesting remote terminal address word, an intended receiver remote terminal address word, and a sign-off indicator word, said sign-off request signal for requesting said control terminal to disassociate said requesting remote terminal from said signal path, h. means for generating and transmitting a digital sign-off response signal on said first channel in a one of said request slots for indicating to said requesting terminal that the previously established communication link is terminated, said sign-off response comprising said requesting terminal address word, said intended receiver terminal address word and said sign-off indicator word.

13. A time division multiple access digital communications system as defined in claim 12 wherein each of said remote subscriber terminals includes:

a. means for receiving said digital frame synchronization signals on said first channel in a one of said time slots, b. means for identifying and selectively receiving the respective ones of said digital request slot assignment signals on said first channel, said selectively received signals having the terminal address word associated with said receiving terminal, c. means for generating and transmitting a one of said digital sign-on request signals on said second channel in a one of said assigned request slots for the respective ones of said terminals, d. means for identifying and selectively receiving the respective ones of said digital sign-on response signals in ones of said time slots on said first channel, said selectively received signals having the terminal address word associated with said receiving terminal, e. means for generating and transmitting said digital data signals on said second channel in a one of said assigned data slots for the respective ones of said terminals, and f. means for identifying and selectively receiving the respective ones of said digital data signals in said time slots on said first channel, said selectively received signals having the terminal address word associated with said receiving terminal. g. means for generating and transmitting said digital sign-off request signal on said second channel in a one of said assigned request slots for the respective ones oF said terminals, and h. means for identifying and selectively receiving the respective ones of said digital sign-off response signals on said first channel, said selectively received signals having the terminal address word associated with said receiving terminal.

14. An apparatus for identifying a subset of time slots from a set having 2n sequentially numbered time slots in a repetitive framed time sequence, where n is an integer, said subset of slots being uniquely defined by a reference slot number, fsn, which is representative of a numbered member of said subset in said framed sequence, and a slot spacing number, m, where m is an integer less than or equal to n and is representative of the spacing between subsequent members of said subset in said framed sequence, said spacing being equal to 2m slots, said apparatus comprising:

a. means for generating a binary coded digital fsn signal representative of said reference slot number, fsn, b. a reference means for identifying the various ones of said set of 2n sequentially numbered time slots in said repetitive framed time sequence, and for generating a sequential binary coded reference signal associated with each of the successively identified time slots, c. means for comparing the m least significant bits of said successively generated reference signals with the m least significant bits of said digital fsn signal representative of said reference slot number, fsn, d. means for generating a control signal when said m least significant bits of said compared signals exactly match, and for generating no such control signal otherwise, said control signal being coincident with and identifying the members of said subset of time slots.

15. A time division multiple access digital communications system for providing a communication link over a common signal path between at least two remote terminals, said system having a plurality of multiple bit digital message signals, each of said signals being disposed in a one of a plurality of time slots in a repetitive framed time sequence, said system comprising:

a. a central control terminal, for receiving digital signals from said remote terminals and for transmitting digital signals to said remote terminals, b. a wideband signal path connected to said control terminal, said signal path including at least one pair of communication channels, the first channel of said pair for transmission of digital signals directed away from said control terminal, and the second of said pair for transmission of digital signals directed toward said control terminal, c. a plurality of remote subscriber terminals, each of said remote terminals having a signal input connected to the first of said pair of channels for receiving digital signals from said control terminal, and a signal output connected to the second of said pair for transmitting digital signals to said control terminal, and each of said remote terminals having an associated binary address word for identification, wherein said central control terminal includes;

a. means for generating and transmitting a digital frame synchronization signal on said first channel in predetermined ones of said time slots, said signal having a binary code word for synchronizing the operation of said remote terminals, b. means for generating and transmitting a digital request slot assignment signal on said first channel in predetermined ones of said time slots, said signal comprising a one of said remote terminal address words and at least one word for assigning to said addressed terminal a set of time slots in a frame to be request slots, said word for defining a first time slot and spacing for a plurality subsequent time slots in a frame, said request slots being assigned to the correspondingly addressed remote terminal for the transmission of digital sign-on request signals, c. means for receiving a digital sign-on Request signal on said second channel from a requesting remote terminal in a one of said associated assigned request slots, said sign-on request signal comprising said requesting remote terminal address word, an intended receiver remote terminal address word and a data rate request word, said sign-on request signal for requesting said control terminal to link said requesting remote terminal via said signal path with a data rate corresponding to said rate request word, d. means for generating and transmitting a digital sign-on response signal on said first channel in a one of said request slots for assigning a set of data slots to said requesting terminal for data transmission, said sign-on response signal comprising said requesting terminal address word, said intended receiver terminal address word and at least one word for identifying a set of data slots, said word for defining a first data slot and spacing for a plurality of subsequent data slots in a frame assigned to said first remote terminal for data transmission, the number of data slots in said set corresponding to the number defined by said data rate request word, e. means for receiving digital data signals on said second channel in ones of said data slots assigned to the respective ones of said remote terminals, said data signals comprising a remote terminal address word and a data word, and f. means for transmitting said received digital data signals on said first channel in ones of said data slots assigned to the respective ones of said remote terminals, said data signals comprising a remote terminal address word and a data word, g. means for receiving a digital sign-off request signal on said second channel from a requesting remote terminal in a one of said associated assigned request slots, said sign-off request signal comprising said requesting remote terminal address word, an intended receiver remote terminal address word, and a sign-off indicator word, said sign-off request signal for requesting said control terminal to disassociate said requesting remote terminal from said signal path, h. means for generating and transmitting a digital sign-off response signal on said first channel in as one of said request slots for indicating to said requesting terminal that the previously established communication link is terminated, said sign-off response comprising said requesting terminal address word, said intended receiver terminal address word and said sign-off indicator word.

16. A time division multiple access digital communications system as defined in claim 15 wherein each of said remote subscriber terminals includes:

a. means for receiving said digital frame synchronization signals on said first channel in a one of said time slots, b. means for identifying and selectively receiving the respective ones of said digital request slot assignment signals on said first channel, said selectively received signals having the terminal address word associated with said receiving terminal, c. means for generating and transmitting a one of said digital sign-on request signals on said second channel in a one of said assigned request slots for the respective ones of said terminals, d. means for identifying and selectively receiving the respective ones of said digital sign-on response signals in ones of said time slots on said first channel, said selectively received signals having the terminal address word associated with said receiving terminal, e. means for generating and transmitting said digital data signals on said second channel in a one of said assigned data slots for the respective ones of said terminals, and f. means for identifying and selectively receiving the respective ones of said digital data signals in said time slots on said first channel, said selectively received signals having the terminal address word associated with said receiving terminal, g. means for generating and transmitting said digital sign-off request signal on said second channel in a one of said assigned request slots for the respective ones of said terminals, and h. means for identifying and selectively receiving the respective ones of said digital sign-off response signals on said first channel, said selectively received signals having the terminal address word associated with said receiving terminal.

17. A time division multiple access digital communications system as defined in claim 16 wherein said central control terminal further includes:

means for allocating predetermined numbers of time slots to selected ones of said remote terminals during each of said framed sequences, said predetermined number of slots being for transmission of said sign-on request signals by the respective ones of said selected terminals to direct said central control terminal to link the requesting remote terminal to said signal path, said predetermined number of slots for providing that said control terminal is responsive to said sign-on request signals of the respective ones of said selected terminals during a predetermined proportion of each of said sequences, whereby said allocation of said predetermined number of time slots provides the respective ones of said remote terminals with a predetermined mean time for access to said signal path.

18. A time division multiple access digital communications system as defined in claim 16 wherein said central control terminal further includes:

means responsive to said received sign-on request signals from said requesting remote terminals to allocate to the respective ones of said requesting remote terminals a selected number of time slots during each of said framed sequences to form a communication link between the ones of said requesting terminals and other terminals connected to said path, said selected number of slots for the respective ones of said requesting remote terminals being determined in response to said rate request word in said sign-on request signal, whereby the information capacity of said signal path is allocated to the respective ones of said requesting remote terminals in accordance with the various sign-on request signals.

19. A time division multiple access digital communication system as described in claim 18 wherein each of said remote terminals includes:

a sign-off request means for transmitting a digital sign-off request signal on said path to request the termination of said established communication link, and wherein said central control terminal includes;

means for receiving from requesting remote terminals said transmitted sign-off request signals and for disassociating said selected number of time slots previously allocated to the respective ones of said requesting terminals to terminate said communication link between ones of said requesting terminals and other terminals connected to said path, whereby the previously allocated portions of the information capacity of said signal path is available to be reallocated to the respective one of said requesting remote terminals in accordance with the various sign-on request signals.

20. A time division multiple access digital communications system as defined in claim 16 wherein said central control terminal further includes:

means for identifying a subset of time slots from a set having 2n sequentially numbered time slots in a repetitive framed time sequence, where n is an integer, said subset of slots being uniquely defined by a reference slot number, fsn, which is representative of a numbered member of said subset in said framed sequence, and a slot spacing number, m, where m is an integer less than or equal to n and is representative of the spacing between members of said subset in said framed sequence, said spacing being equal to 2m slots, said apparatus comprising;

means for generating a binary coded digital fsn signal representative of said reference slot number, fsn, a reference means for identifying the various ones of said set of 2n sequentially numbered time slots in said repetitive framed time sequence, and for generating a sequential binary coded reference signal associated with each of the successively identified time slots, means for comparing the m least significant bits of said successively generated reference signals with the m least significant bits of said digital fsn signal representative of said reference slot number, fsn, means for generating a control signal when said m least significant bits of said compared signals exactly match, and for generating no such control signal otherwise, said control signal being coincident with and identifying the members of said subset of time slots.