Distributed checksum calculation for communication packets
A packet generator includes a checksum calculator configured to distinguish, in a communication packet belonging to a sequence of packets, between (i) one or more constant values of a header of the packet, the one or more constant values remaining unchanged across the packets in the sequence, (ii) a payload of the packet, and (iii) one or more variable values of the header, the one or more variable values changing among the packets in the sequence, to determine a constant-values partial checksum calculated over the constant values of the header, to calculate a payload partial checksum over the payload, to calculate a final checksum value for the packet based on (i) the constant-values partial checksum, (ii) the payload partial checksum and (iii) the variable values of the header, and to insert the final checksum value into the packet. An egress interface transmits the packet over a network.
1. A packet generator, comprising:
a checksum calculator, configured to:
distinguish, in a communication packet belonging to a sequence of communication packets, between (i) one or more constant values of a header of the communication packet, the one or more constant values remaining unchanged across the communication packets in the sequence, (ii) a payload of the communication packet, and (iii) one or more variable values of the header of the communication packet, wherein the one or more variable values span a first number of data words and change among the communication packets in the sequence;
determine a constant-values partial checksum, which is calculated over the constant values of the header and remains unchanged across the communication packets in the sequence;
calculate a payload partial checksum over the payload;
calculate a final checksum value for the communication packet based on (i) the constant-values partial checksum, (ii) the payload partial checksum and (iii) the variable values of the header, by rearranging the variable values of the header in a second number of data words, smaller than the first number, and calculating the final checksum over the second number of data words; and
insert the final checksum value into the communication packet; and
an egress interface, configured to transmit the communication packet, including the final checksum value, over a communication network.
2. The packet generator according to claim 1 , wherein the checksum calculator is configured to determine the constant-values partial checksum and to calculate the payload partial checksum independently of one another.
3. The packet generator according to claim 1 , wherein the checksum calculator is configured to determine the constant-values partial checksum before the payload is received in the packet generator.
4. The packet generator according to claim 1 , wherein the checksum calculator is configured to calculate the constant-values partial checksum upon initialization of the packet generator and to store the calculated constant-values partial checksum in a memory, or to read from the memory an offline-calculated constant-values partial checksum.
5. The packet generator according to claim 1 , wherein the header of the communication packet spans one or more data words, and wherein the checksum calculator is configured to determine the constant-values partial checksum by zeroing any bits of the data words that do not belong to the constant values of the header, and then calculating the constant-values partial checksum over non-zeroed bits of the data words corresponding to the constant values.
6. The packet generator according to claim 1 , wherein the checksum calculator is configured to calculate the payload partial checksum over the payload in parallel with the payload being written into the memory buffer.
7. The packet generator according to claim 1 , wherein the checksum calculator is configured to calculate the final checksum value in parallel with transmission of the communication packet, and to complete calculation of the final checksum value and insertion of the final checksum value into the communication packet before a transmission time of the final checksum value.
8. The packet generator according to claim 1 , further comprising a transmit (TX) First-In First-Out (FIFO) buffer configured to hold at least the payload of the communication packet, wherein the checksum calculator comprises:
input-side logic, which is coupled to an input of the FIFO buffer and configured to insert the payload partial checksum into a status word that propagates via the FIFO buffer together with the payload; and
output-side logic, which is coupled to an output of the FIFO buffer and configured to extract the status word from the FIFO buffer, calculate the final checksum value based on the payload partial checksum in the status word, and insert the final checksum value into the communication packet.
9. A packet generation method, comprising:
in a communication packet belonging to a sequence of communication packets, distinguishing between (i) one or more constant values of a header of the communication packet, the one or more constant values remaining unchanged across the communication packets in the sequence, (ii) a payload of the communication packet, and (iii) one or more variable values of the header of the communication packet, wherein the one or more variable values span a first number of data words and change among the communication packets in the sequence;
determining a constant-values partial checksum, which is calculated over the constant values of the header and remains unchanged across the communication packets in the sequence;
calculating a payload partial checksum over the payload;
calculating a final checksum value for the communication packet based on (i) the constant-values partial checksum, (ii) the payload partial checksum and (iii) the variable values of the header, by rearranging the variable values of the header in a second number of data words, smaller than the first number, and calculating the final checksum over the second number of data words;
inserting the final checksum value into the communication packet; and
transmitting the communication packet, including the final checksum value, over a communication network.
10. The method according to claim 9 , wherein determining the constant-values partial checksum and calculating the payload partial checksum are performed independently of one another.
11. The method according to claim 9 , wherein determining the constant-values partial checksum is performed before the payload is received in the packet generator.
12. The method according to claim 9 , wherein determining the constant-values partial checksum comprises calculating the constant-values partial checksum upon initialization of the packet generator and storing the calculated constant-values partial checksum in a memory, or reading from the memory an offline-calculated constant-values partial checksum.
13. The method according to claim 9 , wherein the header of the communication packet spans one or more data words, and wherein determining the constant-values partial checksum comprises zeroing any bits of the data words that do not belong to the constant values of the header, and then calculating the constant-values partial checksum over non-zeroed bits of the data words corresponding to the constant values.
14. The method according to claim 9 , wherein calculating the payload partial checksum over the payload is performed in parallel with the payload being written into the memory buffer.
15. The method according to claim 9 , wherein calculating the final checksum value comprises calculating the final checksum value in parallel with transmission of the communication packet, and completing calculation of the final checksum value and insertion of the final checksum value into the communication packet before a transmission time of the final checksum value.
16. The packet generator according to claim 9 , further comprising holding at least the payload of the communication packet in a transmit (TX) First-In First-Out (FIFO) buffer, wherein calculating the final checksum value comprises:
inserting the payload partial checksum into a status word that propagates via the FIFO buffer together with the payload; and
extracting the status word from the FIFO buffer, calculating the final checksum value based on the payload partial checksum in the status word, and inserting the final checksum value into the communication packet.