SONET DS-N desynchronizer
First Claim
1. An apparatus for receiving a stream of SONET data comprised of overhead information including positive and negative pointer adjustments and a SONET SPE payload for desynchronizing the SONET SPE payload to a DS-N type data, comprising:
- first counting means for generating a first count in synchronism with a first clock having a first frequency;
second counting means for generating a second count in synchronism with a desynchronized clock having a second frequency;
buffer means, coupled to said first and second counting means, for storing said SONET SPE payload at a location corresponding to said first count in synchronism with said first clock, and for outputting DS-N type data from a location corresponding to said second count in synchronism with said desynchronized clock;
offset means, coupled to said first and second counting means, for determining a difference between said first count and said second count, and for outputting an offset signal representative thereof;
pointer adjustment means, responsive to said overhead information and said positive and negative pointer adjustments, for monitoring said positive and negative pointer adjustments which respectively indicate the reception of said SONET SPE payload after and before a nominal time, and for outputting a count signal representative of the pointer adjustments accumulated over a predetermined period of time;
clock generating means, responsive to a control signal, for generating said desynchronized clock; and
control means, coupled to said offset means and pointer adjustment means, for generating said control signal in response to said offset signal and said count signal so as to adjust said second frequency of said desynchronized clock such that said difference between said first and second count is maintained at a predetermined value.
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Accused Products
Abstract
A SONET/DS-N desynchronizer and method for receiving an incoming stream of SONET (Synchronous Optical NETwork) data, having a controller for controlling numerically controlled oscillator and clock circuit which provide a desynchronized clock for smoothly adapting the rate at which data is retrieved from a data buffer to the rate at which the incoming SONET data is stored in the data buffer. Pointer adjustments are processed separately from the SONET SPE payload frequency tracking. That is, the processing of pointers, which indicates a change in the phase of the SONET SPE payload, includes detecting negative or positive pointer hits by monitoring, for example, the H1, H2 bytes in the transport overhead, and advancing or retarding the phase over a predetermined period of time. On the other hand, the SONET SPE payload frequency tracking includes detecting positive or negative buffer offsets by monitoring the buffer offset signal OFFSET, and increasing or decreasing, respectively, the tuning word to compensate for the detected positive or negative buffer offset.
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Citations
17 Claims
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1. An apparatus for receiving a stream of SONET data comprised of overhead information including positive and negative pointer adjustments and a SONET SPE payload for desynchronizing the SONET SPE payload to a DS-N type data, comprising:
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first counting means for generating a first count in synchronism with a first clock having a first frequency; second counting means for generating a second count in synchronism with a desynchronized clock having a second frequency; buffer means, coupled to said first and second counting means, for storing said SONET SPE payload at a location corresponding to said first count in synchronism with said first clock, and for outputting DS-N type data from a location corresponding to said second count in synchronism with said desynchronized clock; offset means, coupled to said first and second counting means, for determining a difference between said first count and said second count, and for outputting an offset signal representative thereof; pointer adjustment means, responsive to said overhead information and said positive and negative pointer adjustments, for monitoring said positive and negative pointer adjustments which respectively indicate the reception of said SONET SPE payload after and before a nominal time, and for outputting a count signal representative of the pointer adjustments accumulated over a predetermined period of time; clock generating means, responsive to a control signal, for generating said desynchronized clock; and control means, coupled to said offset means and pointer adjustment means, for generating said control signal in response to said offset signal and said count signal so as to adjust said second frequency of said desynchronized clock such that said difference between said first and second count is maintained at a predetermined value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An apparatus for receiving a stream of SONET data comprised of overhead information including positive and negative pointer adjustments and a SONET SPE payload for desynchronizing the SONET SPE payload to a DS-N type data, comprising:
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first clock means for generating a first clock having a first frequency; second clock means for generating a desynchronized clock having a second frequency; buffer means, coupled to said first and second clock means, for storing said SONET SPE payload in synchronism with said first clock, and for outputting DS-N type data in synchronism with said desynchronized clock; offset means for determining a degree of fullness of said buffer, and for outputting an offset signal representative thereof; pointer adjustment means, responsive to said overhead information and said positive and pointer adjustments, for monitoring said positive and negative pointer adjustments, which respectively indicate the reception of said SONET SPE payload after and before a nominal time, and for outputting a count signal representative of the pointer adjustments accumulated over a predetermined period of time; and control means, coupled to said offset means and pointer adjustment means, for generating a control signal in response to said offset signal and said count signal so as to vary said second frequency of said desynchronized clock such that said buffer maintains a predetermined degree of fullness. - View Dependent Claims (12, 13, 14, 15, 16, 17)
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Specification