Buffer-to-Buffer Credit Recovery via Link Reset Synchronization
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Solution Overview
Problem
The Fibre Channel network's credit recovery mechanism is inefficient, leading to performance degradation due to lost buffer-to-buffer credits, especially in complex and high-bandwidth environments, where credits are often corrupted or not properly restored until a link reset occurs.
Innovation Solution
A buffer-to-buffer credit recovery mechanism is implemented by exchanging primitive control signals and parameters during the login sequence, with synchronization between ports achieved through the Link Reset protocol negotiation, ensuring no frames or R_RDYs are exchanged during credit recovery, and resetting credit recovery counters and BB credits as needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the conventional credit recovery mechanism is used, then credit recovery is possible, but performance degradation occurs due to inefficiency and delayed restoration
Solution Approach 1:
The patent applies preliminary action by enabling credit recovery during the Link Reset protocol negotiation phase, before normal data transmission resumes. The receiving port proactively counts frames and R_RDYs during the link reset process and restores credits in advance, ensuring that credit recovery is completed before the next data session begins, thus eliminating performance degradation.
Solution Approach 2:
The patent implements feedback mechanisms where the receiving port tracks and counts the number of frames and R_RDYs received during link reset, comparing these counts against expected values to determine lost credits. This feedback loop enables accurate detection and restoration of lost buffer-to-buffer credits, improving both reliability and productivity.
2Reliability
If Link Reset protocol is used for credit recovery, then lost credits can be restored, but frames or R_RDYs may be lost during the reset process
Solution Approach 1:
The patent extracts the credit recovery function from the normal data transmission process and integrates it into the Link Reset protocol. By separating these functions, the patent ensures that credit recovery occurs in a controlled environment where frame loss is prevented, as the link reset process itself becomes the vehicle for safe credit restoration without interfering with ongoing data sessions.
Solution Approach 2:
The patent performs credit recovery as a preliminary action during the link reset negotiation, before normal data transmission resumes. This timing ensures that all frame counting and credit restoration occurs in a controlled state where no data frames are being transmitted, thereby preventing frame loss while restoring credits.
3Reliability
If buffer to buffer credit control is implemented, then frame loss is prevented, but performance degradation occurs when credits are lost and not restored
Solution Approach 1:
The patent enhances the feedback mechanism by having the receiving port continuously count frames and R_RDYs during link reset operations. This feedback enables the system to detect lost credits accurately and restore them promptly, preventing the performance degradation that would otherwise occur when credits are lost and not restored.
Solution Approach 2:
The patent restores lost credits as a preliminary action during the link reset process, before normal data transmission begins. This ensures that the buffer-to-buffer credit control mechanism is fully functional and ready to prevent frame loss, while also restoring throughput by eliminating the delay associated with waiting for credit restoration.
Data Source
AI summary
A buffer to buffer credit recovery mechanism is disclosed in which the ports involved in the credit recovery operation are synchronized while credit recovery is being enabled and during a credit recovery operation when credit recovery parameters are being reset. Buffer to buffer credit recovery involves exchanging primitive control signals and parameters during the login sequence to enable credit recovery. Once credit is lost; there may be a need for resetting a link to reset the credit recovery counters and BB credits. Both of these processes require synchronization between the ports involved in the credit recovery mechanism. This synchronization is achieved by enabling credit recovery during the Link Reset protocol negotiation and ensuring that no frames or R_RDYs are exchanged during the procedure.