ATM cell detector
First Claim
1. Method for detecting, from a bit stream, the beginning of data packets such as ATM data cells, which data packets originate from different sources and are combined into one stream of data packets, each data packet being preceded by a preamble which comprises at least a gap, formed by a number of 0-bits, and a unique word UW having a unique word reference value which is formed by a specific combination of 0-bits and 1-bits and which unique word reference value has a length of b(uw) bits, wherein the unique word UW is preceded by a bit alignment word AW having an alignment word reference value which is formed by, beginning with a 1-bit, a specific combination of 0-bits and 1-bits and which has a length of b(aw) bits,the method comprising the following steps being carried out successively for the purpose of detecting a new data packet after a previous data packet has ended:
- detecting, from a bit stream, the first 1-bit to occur and calculating, for a first detected bit string B(dl), which begins with the first detected 1-bit and which has a length b(dl) equal to the number of bits b(aw) of the alignment word reference value plus the number of bits b(uw) of the unique word reference value, a Hamming distance hd(1) between the first detected bit string B(dl) and a first reference bit string B(aw+uw) being equal to the alignment word reference value plus the unique word reference value;
calculating, for a second detected bit string B(d2), which begins with the detected first 1-bit, (b(aw)-1) bits after said detected first 1-bit occurs and which has a length b(d2) equal to the number of bits b(uw) of the unique word reference value, the Hamming distance hd(2) between the second detected bit string B(d2) and a second reference bit string B(uw) which is equal to the unique word reference value;
detecting, from the bit stream, a second 1-bit to occur and calculating, for a third detected bit string B(d3), which begins with the second detected 1-bit and which has a length b(d3) equal to the number of bits b(aw) of the alignment word reference value plus the number of bits b(uw) of the unique word reference value, the Hamming distance hd(3) between the third detected bit string B(d3) and the third reference bit string B(aw+uw) which is equal to the alignment word reference value plus the unique word reference value;
calculating the position of the first bit of a new data packet on the basis of at least one of the calculated Hamming distances hd(1), hd(2) and hd(3) according to the following rules, where p is the number of bits of possible further preamble words which follow the gap, the alignment word AW and the unique word UW;
if hd(1)=0 or hd(1)=l, then the first bit of the data packet is situated at a distance of b(aw+uw)+p bits after the detected first 1 -bit;
if hd(2)=0, then the first bit of the data packet is situated at a distance of b(aw+uw)-l+p bits after the detected first 1-bit; and
if hd(3)=0, then the first bit of the data packet is situated at a distance of b(aw+uw)+p bits after the detected second 1-bit.
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Accused Products
Abstract
Method for detecting data packets, such as ATM data cells. The preamble comprises a bit alignment word (AW) and a unique word (UW). Successively, the Hamming distances, hd'"'"'s, are calculated from the first detected l-bit, over a length of AW plus UW, then from the next bit over a length of UW, and finally from the second 1-bit, again over a length of AW plus UW. The position of the first bit of the detected data packet is then calculated on the basis of the hd values thus calculated.
10 Citations
2 Claims
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1. Method for detecting, from a bit stream, the beginning of data packets such as ATM data cells, which data packets originate from different sources and are combined into one stream of data packets, each data packet being preceded by a preamble which comprises at least a gap, formed by a number of 0-bits, and a unique word UW having a unique word reference value which is formed by a specific combination of 0-bits and 1-bits and which unique word reference value has a length of b(uw) bits, wherein the unique word UW is preceded by a bit alignment word AW having an alignment word reference value which is formed by, beginning with a 1-bit, a specific combination of 0-bits and 1-bits and which has a length of b(aw) bits,
the method comprising the following steps being carried out successively for the purpose of detecting a new data packet after a previous data packet has ended: -
detecting, from a bit stream, the first 1-bit to occur and calculating, for a first detected bit string B(dl), which begins with the first detected 1-bit and which has a length b(dl) equal to the number of bits b(aw) of the alignment word reference value plus the number of bits b(uw) of the unique word reference value, a Hamming distance hd(1) between the first detected bit string B(dl) and a first reference bit string B(aw+uw) being equal to the alignment word reference value plus the unique word reference value; calculating, for a second detected bit string B(d2), which begins with the detected first 1-bit, (b(aw)-1) bits after said detected first 1-bit occurs and which has a length b(d2) equal to the number of bits b(uw) of the unique word reference value, the Hamming distance hd(2) between the second detected bit string B(d2) and a second reference bit string B(uw) which is equal to the unique word reference value; detecting, from the bit stream, a second 1-bit to occur and calculating, for a third detected bit string B(d3), which begins with the second detected 1-bit and which has a length b(d3) equal to the number of bits b(aw) of the alignment word reference value plus the number of bits b(uw) of the unique word reference value, the Hamming distance hd(3) between the third detected bit string B(d3) and the third reference bit string B(aw+uw) which is equal to the alignment word reference value plus the unique word reference value; calculating the position of the first bit of a new data packet on the basis of at least one of the calculated Hamming distances hd(1), hd(2) and hd(3) according to the following rules, where p is the number of bits of possible further preamble words which follow the gap, the alignment word AW and the unique word UW; if hd(1)=0 or hd(1)=l, then the first bit of the data packet is situated at a distance of b(aw+uw)+p bits after the detected first 1 -bit; if hd(2)=0, then the first bit of the data packet is situated at a distance of b(aw+uw)-l+p bits after the detected first 1-bit; and if hd(3)=0, then the first bit of the data packet is situated at a distance of b(aw+uw)+p bits after the detected second 1-bit.
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2. System for detecting, from a bit stream, the beginning of data packets such as ATM data cells, each data packet being preceded by a preamble which comprises at least a gap, formed by a number of 0-bits, and a unique word UW having a unique word reference value which is formed by a specific combination of 0-bits and 1-bits and which unique word reference value has a length of b(uw) bits, wherein the unique word UW is preceded by a bit alignment word AW having an alignment word reference value which is formed by, beginning with a 1-bit, a specific combination of 0-bits and 1-bits and which has a length of b(aw) bits, the system detecting a subsequent data packet after a first data packet has ended, the system comprising:
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a first detection unit (1) for detecting, from the bit stream, the first 1-bit after said first data packet has ended; a first processingq unit (2) for calculating, for a first detected bit string B(dl), which begins with the first 1-bit detected by the first detection unit (1) and which has a length b(dl) equal to the number of bits b(aw) of the alignment word reference value plus the number of bits b(uw) of the unique word reference value, the Hamming distance hd(1) between the first detected bit string B(dl) and a first reference bit string B(aw+uw) being equal to the alignment word reference value plus the unique word reference value; a pointer unit (3) for indicating the (b(aw)-l)th bit after the first detected 1-bit; a second processing unit (4) for calculating, for a second detected bit string B(d2), which begins with the bit indicated by the pointer unit (3) , (b(aw)-1) bits after the first 1-bit detected by the first detection unit (1), and which has a length b(d2) equal to the number of bits b(uw) of the unique word reference value, the Hamming distance hd(2) between the second detected bit string B(d2) and a second reference bit string B(uw) being equal to the unique word reference value; a second detection unit (5) for detecting the second 1-bit in the bit stream, after said first data packet has ended; a third processing unit (6) for calculating, for a third detected bit string B(d3) which begins with the second 1-bit detected by the second detection unit (5) and which has a length b(d3) equal to the number of bits b(aw) of the alignment word reference value plus the number of bits b(uw) of the unique word reference value, the 0-bits and 1-bits and which has a length of b(aw) bits, Hamming distance hd(3) between the third detected bit string B(d3) and the third reference bit string B(aw+uw) being equal to the alignment word reference value plus the unique word reference value; a fourth processing unit (7) for calculating the position of the first bit of the following data packet on the basis of at least one of the calculated Hamming distances hd(1), hd(2) and hd(3) calculated by at least one of said processing units according to the following rules, where p is the number of bits of possible further preamble words which follow said gap, the alignment word AW and the unique word UW; if hd(1)=O or hd(1)=1 , then the first bit of the data packet is situated at a distance of b(aw+uw)+p bits after the detected first 1-bit; if hd(2)=O, then the first bit of the data packet is situated at a distance of b(aw+uw)-1+p bits after the detected first 1-bit; and if hd(3)=O, then the first bit of the data packet is situated at a distance of b(aw+uw)+p bits after the detected second 1-bit.
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Specification