TCP Checksum Offload Latency Reduction via Preliminary Action
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Solution Overview
Problem
Conventional TCP processing incurs frame transmission latency as it waits for the entire payload to be received before calculating the TCP checksum, which delays the transmission of frames.
Innovation Solution
Implementing the TCP alternate checksum option, which allows frame transmission to begin before checksum calculation by using a predetermined value and computing an integrity check value using a shared key, reducing the need for extensive memory buffering and enabling transmission without waiting for complete payload reception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the TCP checksum is calculated after receiving the entire payload data, then the checksum accuracy is ensured, but the frame transmission latency increases
Solution Approach 1:
The patent applies preliminary action by transmitting the frame before the TCP checksum calculation is complete. The NIC begins frame transmission as soon as the payload data is received, inserting a placeholder or partial checksum, and completes the checksum calculation afterward. This allows transmission to start earlier without sacrificing checksum accuracy, directly resolving the latency-accuracy contradiction.
2Measurement precision
If the entire payload data is stored in dedicated memory before checksum calculation, then the checksum computation is accurate, but the memory buffering requirement increases
Solution Approach 1:
The patent applies preliminary action by initiating frame transmission before the checksum calculation is complete. This eliminates the need to store the entire payload in dedicated memory beforehand, as the frame can be transmitted incrementally or with a placeholder checksum that is completed afterward. This significantly reduces the memory buffering requirement while maintaining checksum accuracy.
3Reliability
If the frame transmission waits for complete payload reception and checksum calculation, then the data integrity is ensured, but the transmission speed decreases
Solution Approach 1:
The patent applies preliminary action by starting frame transmission before the checksum calculation is complete. The NIC can transmit the frame with a placeholder checksum or begin transmission of already-received data segments while continuing to calculate the checksum. This maintains data integrity through post-transmission checksum verification while significantly improving transmission speed by eliminating the waiting period.
Data Source
AI summary
An alternate checksum option for transmitting TCP frame data is used that does not require computing a TCP checksum. Instead, an integrity check value is computed and placed in the ESP authentication portion near the end of the frame. Transmission of a portion of the TCP frame data may begin before all of the TCP frame data is received by a TCP checksum offload device because the integrity check value is inserted at the end of the frame. Furthermore, the integrity check value is computed using a static key or a dynamic key may be computed to cover a greater portion of the frame compared with ESP authentication specified by the IPsec standard.