Fibre Channel ISL B2B Credit Sizing by Real-Time Latency

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Solution Overview

Problem

In Fibre Channel Storage Area Networks (SANs), congestion and slow data transmission occur due to insufficient Buffer to Buffer Credits (B2B Credits) on Inter Switch Links (ISLs), requiring conventional methods to temporarily take the link down for latency measurement, which disrupts operation.

Innovation Solution

A method and system for determining the minimum number of B2B Credits needed on an ISL by communicating frames with timestamps between switches, calculating round trip link latency, and adjusting buffer credits to minimize congestion without disrupting the link.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional approaches are used to measure ISL latency, then measurement precision can be achieved, but the link must be taken down temporarily causing operational disruption

Engineering Contradiction:

ImproveISL latency measurementVSAvoidlink operational continuity

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent implements a feedback mechanism where switches exchange timestamped frames to measure latency. The receiving switch timestamps the received frame and sends it back to the initiating switch, which calculates round-trip latency using the time difference. This continuous feedback loop allows latency measurement without disrupting link operation.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent performs preliminary actions by having switches pre-configured with timestamping capabilities and B2B credit tracking mechanisms. Before actual latency measurement is needed, the infrastructure is ready to execute rapid timestamp exchange operations, enabling measurement without requiring link disruption.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If insufficient B2B Credits are configured on ISL, then link utilization can be improved, but congestion and slow data transmission occur

Engineering Contradiction:

Improvelink utilizationVSAvoidcongestion

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent uses feedback from latency measurements and frame transmission observations to dynamically adjust B2B credit configurations. By continuously monitoring link performance and using the timestamp-based latency data, the system can optimize credit counts to prevent congestion while maintaining high link utilization.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the parameter of B2B credit count based on measured latency and congestion conditions. By adjusting this parameter dynamically rather than using fixed values, the system optimizes the balance between link utilization and congestion prevention, adapting to changing network conditions.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If B2B Credits are increased to prevent congestion, then data transmission efficiency improves, but networking resources are consumed

Engineering Contradiction:

Improvedata transmission efficiencyVSAvoidnetworking resources

Core Design Contradiction:

ProductivityVSQuantity of substance

Solution Approach 1:

The patent optimizes the B2B credit parameter to the minimum necessary value that prevents congestion. By using latency measurements to calculate the exact credit requirement rather than over-provisioning, the system achieves good transmission efficiency while minimizing networking resource consumption.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies partial action by configuring only the minimum necessary B2B credits required to prevent congestion, rather than using excessive credit counts. This optimized approach achieves sufficient transmission efficiency without wasting networking resources on unnecessary credit reserves.

Inventive Principle:

Principle #16Partial or excessive action

4Loss of time

If link latency is increased, then more time is available for frame processing, but data transmission speed decreases

Engineering Contradiction:

Improveframe processing timeVSAvoiddata transmission speed

Core Design Contradiction:

Loss of timeVSSpeed

Solution Approach 1:

The patent uses feedback from timestamped frame exchange to measure actual link latency and use this information to optimize B2B credit configuration. By knowing the real latency through continuous measurement, the system can adjust credits to minimize processing time while maintaining transmission speed.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent changes the B2B credit parameter based on measured latency to optimize the balance between processing time and transmission speed. By adjusting credits according to actual link conditions rather than assuming fixed latency, the system achieves optimal performance.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS20250293988A1Method and Procedure for Real Time Determination of Minimum Fibre Channel Buffer to Buffer Credits on an Inter Switch Link

Publication Date: 2025.09.18 CISCO TECHNOLOGY INC

AI summary

A method for the real time determination of minimum fibre channel buffer to buffer credits on an inter switch link. In one particular embodiment, a method includes communicating a first frame to a receiving switch with a first timestamp, receiving a second frame with a second and third timestamp, adding a fourth timestamp to the second frame, calculating the round trip link latency time value using the first timestamp, the second timestamp, the third timestamp, and the fourth timestamp, and calculating the minimum number of buffer to buffer credits to be configured on the link to nondisruptively transmit traffic.