Nortel Networks Corporation

Notel Networks Corporation

David William Wiggins

David Michael Goodman

James A Shields

Christopher David Murton

John Paul Russell

Christopher Thomas William Ramsden

A transmission apparatus and a method for operating the apparatus comprises means for controlling flow of frame based data transmitted from a local frame based data channel interface over a synchronous digital network. The method of operation comprises the transmitter receiving frame based data at a first rate whereafter a buffer is configured to receive the frame based data. A data amount threshold level for the buffer is pre-determined whereafter, with respect to the threshold level, an amount of transmitted frame based data that has been received is monitored. In response to monitoring the amount of data received, a signal, in the form of a pause frame, is generated wherein the signal is configurable to adapt the rate of transmission from the frame based data channel interface. Working in conjunction with the transmission means there is also provided a receiver for controlling flow of frame based data, received from a synchronous digital network, to a frame based data channel interface. The receiver is configured to receive the frame based data at a first rate whereafter a buffer is configured to receive the frame based data. Upon pre-determining a data amount threshold level for the buffer an amount of frame based data received is monitored with respect to the threshold level. In response to monitoring the amount of data received, a signal is generated in the form of a pause frame, wherein the pause frame signal is configurable to adapt the first transmission rate of the frame based data over the synchronous digital network to a second rate. In this way, the rate of transmission from a local Ethernet switch may be controlled and the rate of receipt of Ethernet based frame data from a synchronous digital network may be controlled. In the latter case pause frames may be incorporated into one or more synchronous digital hierarchy virtual containers.

Flow control of frame based data over a synchronous digital network

A method and apparatus for controlling the read clock signal rate of a First-In First-Out data memory is provided. A control signal for controlling the read clock signal rate is derived from an error signal, wherein the level of data contained in the FIFO is used to generate the error signal. The control signal includes an integral element, which comprises the error signal, scaled by a first paramater and integrated over time, and a proportional element, which comprises the error signal scaled by a second parameter. In accordance with the invention, at least one of the first and second scaling parameters is varied in accordance with the absolute error signal level. In a preferred embodiment, the or each parameter is varied as an exponential function of the absolute error signal level. This results in the bandwidth of the apparatus varying exponentially with the absolute error signal level. The dynamic or adaptive nature of the bandwidth enables the apparatus to provide an output data stream with relatively low wander or jitter under normal operating conditions while preventing data loss due to FIFO overflow or underflow in extreme operating conditions. The invention has particular application in the desynchronization of plesiochronous data elements from a synchronous transmission format in a telecommunications network system.

Method and apparatus for controlling the read clock signal rate of a first-in first-out (FIFO) data memory

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Belfast, United Kingdom

David William Wiggins