Method and system for transmitting buffered data packets on a communications network

Claim 1

A method of transmitting data packets in time slots on a communications network having first and second unidirectional buses which are respectively directed in downstream and upstream directions and a succession of access units coupled between the buses, said method including the steps of: forming a distributed queue of such data packets by establishing in each access unit a queue of the data packets therein which are to be transmitted on the first unidirectional bus; transmitting a request flag on the second unidirectional bus by each access unit for each data packet in the queue; keeping count in each access unit of the number of request flags passing such access unit on the second unidirectional bus; and transmitting a data packet at the head of the queue in an access unit when a predetermined number of empty time slots has passed said access unit on the first bus; characterized in that: at the time a further data packet which had been received in an access unit and added to the queue therein reaches a selected position in the queue, at which position there are a predetermined number of other data packets between said further data packet and the head of the queue, a request flag is transmitted on the second bus by said access unit; and said further data packet is transmitted by said access unit in the first empty time slot after passage of a predetermined number of empty time slots past said access unit on the first bus, said predetermined number of empty time slots being equal to the total number of data packets in the distributed queue for which request flags had already been transmitted at the time said further data packet reaches said selected position in said queue.

Claim 2

A method of transmitting data packets in time slots on a communications network having first and second unidirectional buses which are respectively directed in downstream and upstream directions and a succession of access units coupled between the buses, said method including the steps of: forming a distributed queue of such data packets by establishing in each access unit a queue of the data packets therein which are to be transmitted on the first unidirectional bus; transmitting a request flag on the second unidirectional bus by each access unit for each data packet in the queue; keeping count in each access unit of the number of request flags passing such access unit on the second unidirectional bus; and transmitting a data packet at the head of the queue in an access unit when a predetermined number of empty time slots has passed said access unit on the first bus; characterized in that: at the time a further data packet which had been received in an access unit and added to the queue therein reaches a selected position in the queue, at which position there are a predetermined number of other data packets between said further data packet and the head of the queue, a request flag is transmitted on the second bus by said access unit; and said further data packet is transmitted by said access unit in the first empty time slot after passage of a predetermined number of empty time slots past said access unit on the first bus, said predetermined number of empty time slots being equal to the total number of data packets in the distributed queue for which request flags had already been transmitted at the time said further data packet reaches said selected position in said queue.

Claim 9

A method of transmitting data packets in time slots on a communications network according to claim represented by a request bit-string at the time it is received by an access unit having a data packet ready for transmission is added to such data packet as said priority value thereof.

Claim 16

A system for transmitting data packets in time slots on a communications network having first and second unidirectional buses which are respectively directed in upstream and downstream directions, and a succession of access units coupled between the busses; each access unit comprising: a request flag counter connected to become incremented by request flags passing on the second bus; a countdown counter connected to become decremented from an initially loaded value to a predetermined end value by successive empty time slots passing on the first bus; a queue buffer for storing data packets received by said access unit and which are to be transmitted on the first bus; and a logic interface adapted to (i) transmit a request flag for each data packet in the queue buffer, (ii) initiate transmission of the data packet at the head of the queue after the countdown counter reaches said predetermined end value, and (iii) reload said countdown counter on the basis of a value accumulated in the request flag counter; characterized in that in each access unit: the queue buffer is adapted to store in combination with each data packet therein a priority value which is shifted with the data packet through the queue buffer; and said logic interface is adapted to (iv) transmit a request flag on the second bus at the time a further data packet in the said buffer reaches a selected stage therein a predetermined number of stages prior to the head of said buffer, (v) store with said further data packet in said buffer a priority value corresponding to the accumulated value in said request counter when said further data packet reaches said selected stage of said buffer, and reset said request counter; and (vi) reload said countdown counter with the priority value of said further data packet in said buffer when said further data packet reaches the head of said buffer.

Claim 17

A system for transmitting data packets in time slots on a communications network having first and second unidirectional buses which are respectively directed in upstream and downstream directions, and a succession of access units coupled between the busses; each access unit comprising: a request flag counter connected to become incremented by request flags passing on the second bus; a countdown counter connected to become decremented from an initially loaded value to a predetermined end value by successive empty time slots passing on the first bus; a queue buffer for storing data packets received by said access unit and which are to be transmitted on the first bus; and a logic interface adapted to (i) transmit a request flag for each data packet in the queue buffer, (ii) initiate transmission of the data packet at the head of the queue after the countdown counter reaches said predetermined end value, and (iii) reload said countdown counter on the basis of a value accumulated in the request flag counter; characterized in that in each access unit: the queue buffer is adapted to store in combination with each data packet therein a priority value which is shifted with the data packet through the queue buffer; and said logic interface is adapted to (iv) transmit a request flag on the second bus at the time a further data packet in the said buffer reaches a selected stage therein a predetermined number of stages prior to the head of said buffer, (v) store with said further data packet in said buffer a priority value corresponding to the accumulated value in said request counter when said further data packet reaches said selected stage of said buffer, and reset said request counter; and (vi) reload said countdown counter with the priority value of said further data packet in said buffer when said further data packet reaches the head of said buffer.