Device for justifying a digital bit stream at regular intervals
First Claim
1. A device for justifying at regular intervals a digital bit stream received from a first synchronous link timed by a first clock and to be sent on a second synchronous link timed by a second clock, said digital bit stream comprising a continuous sequence of rows of bits, each row comprising a fixed total number of bits but including a payload comprising a variable number of bits and a header comprising a variable number of bits, the numbers of bits varying according to whether said row has been subjected to positive justification, negative justification or no justification, the device including:
- a buffer memory into which said payload is written under the control of said first clock and from which said payload is read under the control of said second clock;
means for calculating a filling value indicative of how full said buffer memory is;
means for comparing said filling value to first and second variable threshold values to produce a negative justification command signal when it is greater than said first threshold value and to produce a positive justification command signal when it is less than said second threshold value; and
means for determining the first and second variable threshold values according to the phase difference between the header of a row received from said first link and the header of a row sent on said second link.
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Accused Products
Abstract
A digital bit stream from a first synchronous link is timed by a first clock and is to be sent over a second synchronous link timed by a second clock. A device for justifying the bit stream at regular intervals includes a buffer memory. Respective pointers supply buffer memory write and read addresses. A value indicating how full the buffer memory is is calculated and compared to first and second threshold values to produce a justification command signal. The first and second variable threshold values are determined according to the phase difference between the header of a row received from the first link and the header of a row sent at the same time on the second link. The device finds an application in gateways at the input of and in telecommunication networks using the synchronous digital hierarchy.
26 Citations
10 Claims
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1. A device for justifying at regular intervals a digital bit stream received from a first synchronous link timed by a first clock and to be sent on a second synchronous link timed by a second clock, said digital bit stream comprising a continuous sequence of rows of bits, each row comprising a fixed total number of bits but including a payload comprising a variable number of bits and a header comprising a variable number of bits, the numbers of bits varying according to whether said row has been subjected to positive justification, negative justification or no justification, the device including:
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a buffer memory into which said payload is written under the control of said first clock and from which said payload is read under the control of said second clock; means for calculating a filling value indicative of how full said buffer memory is; means for comparing said filling value to first and second variable threshold values to produce a negative justification command signal when it is greater than said first threshold value and to produce a positive justification command signal when it is less than said second threshold value; and means for determining the first and second variable threshold values according to the phase difference between the header of a row received from said first link and the header of a row sent on said second link. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification