Cell-based clock recovery device
AssigneeNewbridge Networks Corporation
InventorNeil Cox
Life of this patent
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Abstract
A clock recovery unit provides a clock recovery function in the receiving entity of a system to implement adaptation of constant bit-rate (CBR) services over an asynchronous transfer mode (ATM) or ATM-like network. Incoming cells are periodically sampled for buffer fill level L.sub.i. The maximum fill level of undelayed cells Lx.sub.j is extracted from successive series of a predetermined whole number M of buffer-fill samples L.sub.i. A frequency adjustment logic unit provides at its output a bit stream at a given clock frequency f.sub.j. The frequency adjustment logic unit makes incremental adjustments to the clock frequency f.sub.j tending to cause the steady state mean of the fill level Lx.sub.j, or its derivative, to move toward zero.
Claims21
A clock recovery unit for providing a clock recovery function in the receiving entity of a system to implement adaptation of constant bit-rate (CBR) services over an asynchronous transfer mode (ATM) or ATM-like network, comprising a buffer for receiving incoming cells;
- a sampling unit for periodically sampling the buffer fill level L.sub.i ;
- an estimation unit for obtaining an estimate Lx.sub.j of the buffer fill level on arrival of substantially undelayed cells from a series of buffer fill-level samples L.sub.i ;
- and a frequency adjustment logic unit providing at its output a control signal at a given clock frequency f.sub.j, said frequency adjustment logic unit making incremental adjustments to said clock frequency f.sub.j to cause the steady state mean of said estimate Lx.sub.j of the buffer fill level on arrival of undelayed cells, or a derivative thereof, to move toward a predefined optimal operating point.
A method of providing a clock recovery function in the receiving entity of a system to implement adaptation of constant bit-rate (CBR) services over an asynchronous transfer mode (ATM) or ATM-like network, comprising the steps of receiving incoming cells in a buffer;
- periodically sampling the buffer fill level L.sub.i ;
- estimating the buffer fill level on arrival of substantially undelayed cells Lx.sub.j from a series of buffer fill-level samples L.sub.i ;
- outputting a control signal at a given clock frequency f.sub.j ;
- and making incremental adjustments to said clock frequency f.sub.j to cause the steady state mean of the estimate Lx.sub.j of the buffer fill level on arrival of undelayed cells, or a derivative thereof, to move toward a predetermined optimal value.
Dependencies are inferred from the claim text.