US5610951A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Efficient ATM cell synchronization
Assignee: Compaq Computer Holding Ltd
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Filing: 1993-06-04
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Granted: 1997-03-11
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Expires: 2013-06-04
Abstract
Abstract A device 11 includes a sync unit 20 to identify and achieve synchronization with the cell boundaries of a 53-byte ATM cell stream. Each cell starts with a 5-byte header in which the 5th byte is a CRC byte. Instead of testing all possible bytes to see whether they are cell boundaries, a CRC circuit 21 computes CRCs for successive 5-byte blocks, under the control of a 5-state header counter 22. If such a block is a header, its CRC is a predetermined value, and a match signal is sent to a logic circuit 23, which starts a 53-state cell counter 24 and stops the header counter 22. A 4-state repeat counter 25 checks that the next 5 blocks checked by the CRC circuit 21 are also headers, as confirmation. Synchronization is achieved within at most 5 cells, because the test period of the testing circuitry (which could be longer than the header length) is coprime with the cell length.
Inventors
- 👤 Peter L. Higginson
- 👤 Anthony N. Berent
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 21:18
CPC Classifications
H; H04; H04L; H04L7/00; H04L7/04; H04L7/048; H04Q; H04Q11/00; H04Q11/04; H04Q11/0428; H04Q11/0478; H04L12/00; H04L12/54; H04L12/56; H04L12/5601; H04L2012/5672; H04L2012/5673; H04L2012/5674
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
147 words
Synchronizing apparatus for identifying cell boundaries in a stream of data signals received from a transmission line, each cell starting with a header including a CRC, each cell having a cell length, each header having a header length, the apparatus comprising: a single CRC check circuit and timing means which select, for testing by the CRC check circuit, non-overlapping but substantially contiguous blocks of signals, each block has a block length greater than the header length, with the blocks being chosen at a spacing which is effectively coprime with the cell length; means for sending a match signal identifying a cell header to a control unit in response to said CRC check circuit computing from the blocks of signals a value matching a predetermined CRC value; and, means for said control unit to verify synchronization with the stream of data signals in response to said match signal.
Claim 2
Dependent Claim
147 words
Synchronizing apparatus for identifying cell boundaries in a stream of data signals received from a transmission line, each cell starting with a header including a CRC, each cell having a cell length, each header having a header length, the apparatus comprising: a single CRC check circuit and timing means which select, for testing by the CRC check circuit, non-overlapping but substantially contiguous blocks of signals, each block has a block length greater than the header length, with the blocks being chosen at a spacing which is effectively coprime with the cell length; means for sending a match signal identifying a cell header to a control unit in response to said CRC check circuit computing from the blocks of signals a value matching a predetermined CRC value; and, means for said control unit to verify synchronization with the stream of data signals in response to said match signal.
Claim 3
Dependent Claim
12 words
Synchronizing apparatus according to claim 1 wherein the blocks are exactly contiguous.
Claim 4
Dependent Claim
36 words
Synchronizing apparatus according to claim 1 or claim 2 wherein each of the blocks has a block length, each said header has a header length, and the block length is the same as the header length.
Claim 5
Dependent Claim
44 words
Synchronizing apparatus according to claim 3 wherein the data signals are bytes, the cell length is 53 bytes, the header length is 5 bytes of which the last byte is a CRC byte, and each of the blocks has a length of 5 bytes.
Claim 6
Dependent Claim
162 words
Synchronizing apparatus for identifying cell boundaries in a stream of data signals received form a transmission line, each cell starting with a header including a CRC, each cell having a length, the apparatus comprising: a header counter to count bytes in said stream of data signals; a single CRC check circuit and timing means which select, for testing by the CRC check circuit, non-overlapping but substantially contiguous blocks of signals, with the blocks being chosen at a spacing which is effectively coprime with the cell length, said CRC check circuit to compute a CRC of a predetermined number of bytes as counted by said header counter; means for sending a match signal identifying a cell header to a control unit in response to said CRC check circuit computing from said predetermined number of bytes a value matching a predetermined CRC value; and, means for said control unit to verify synchronization with the stream of data signals in response to said match signal.
Claim 7
Dependent Claim
162 words
Synchronizing apparatus for identifying cell boundaries in a stream of data signals received form a transmission line, each cell starting with a header including a CRC, each cell having a length, the apparatus comprising: a header counter to count bytes in said stream of data signals; a single CRC check circuit and timing means which select, for testing by the CRC check circuit, non-overlapping but substantially contiguous blocks of signals, with the blocks being chosen at a spacing which is effectively coprime with the cell length, said CRC check circuit to compute a CRC of a predetermined number of bytes as counted by said header counter; means for sending a match signal identifying a cell header to a control unit in response to said CRC check circuit computing from said predetermined number of bytes a value matching a predetermined CRC value; and, means for said control unit to verify synchronization with the stream of data signals in response to said match signal.
Claim 8
Dependent Claim
16 words
The apparatus as in claim 5 wherein said predetermined number of bytes further comprises 5 bytes.
Claim 9
Dependent Claim
70 words
The apparatus as in claim 5 further comprising: a cell counter to count bytes in said stream of data signals; and, wherein said header counter counts said predetermined number of bytes in successive headers after said cell counter indicates a cell boundary during reception of said stream of data, and said CRC check circuit indicates whether a CRC value computed for each said successive header has said predetermined CRC value.
Claim 10
Dependent Claim
40 words
The apparatus as in claim 7 further comprising: a repeat counter to count a predetermined number of successive headers having said CRC check circuit compute said predetermined CRC value, to enable said apparatus to accept said headers as true headers.
Claim 11
Dependent Claim
15 words
The apparatus as in claim 8 wherein said predetermined number of successive headers is 4.
Claim 12
Dependent Claim
37 words
The apparatus as in claim 8 wherein said repeat counter signals said synchronization apparatus that synchronization with said data stream has been achieved, in the event that said repeat counter counts said predetermined number of successive headers.
Claim 13
Dependent Claim
165 words
Synchronizing apparatus for identifying cell boundaries in a stream of data signals received from a transmission line, each cell starting with a header including a CRC, each cell having a length, the apparatus comprising: a single CRC check circuit and timing means which select, for testing by the CRC check circuit, non-overlapping but substantially contiguous blocks of signals, with the blocks being chosen at a spacing which is effectively coprime with the cell length; means for sending a match signal identifying a cell header to a control unit in response to said CRC check circuit computing from the blocks of signals a value matching a predetermined CRC value; a cell counter to count bytes in said stream of data signals in response to said match signal, and to define a cell boundary after counting a predetermined number of cell bytes; and, means for said control unit to verify synchronization with the stream of data signals in response to said match signal and said cell boundary.
Claim 14
Dependent Claim
165 words
Synchronizing apparatus for identifying cell boundaries in a stream of data signals received from a transmission line, each cell starting with a header including a CRC, each cell having a length, the apparatus comprising: a single CRC check circuit and timing means which select, for testing by the CRC check circuit, non-overlapping but substantially contiguous blocks of signals, with the blocks being chosen at a spacing which is effectively coprime with the cell length; means for sending a match signal identifying a cell header to a control unit in response to said CRC check circuit computing from the blocks of signals a value matching a predetermined CRC value; a cell counter to count bytes in said stream of data signals in response to said match signal, and to define a cell boundary after counting a predetermined number of cell bytes; and, means for said control unit to verify synchronization with the stream of data signals in response to said match signal and said cell boundary.
Claim 15
Dependent Claim
16 words
The apparatus as in claim 11 wherein said predetermined number of cell bytes is 54 bytes.
References Cited (Backward Citations)
US4016548A
Cited
US3982074A
Cited
US4594708A
Cited
EP0264064A2
Cited
US4922438A
Cited
US4947388A
Cited
US4962498A
Cited
US5123013A
Cited
US5189666A
Cited
US5155487A
Cited
US5282215A
Cited
US5054020A
Cited
US5193088A
Cited
US5251215A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 2000-03-10 | 2000-09-09 | 2001-03-11 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2004-03-10 | 2004-09-09 | 2005-03-11 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2008-03-10 | 2008-09-09 | 2009-03-11 | $7700.00 | Window Closed / Lapsed |