FC-AL Bridge Arbitration Fairness via Dynamic T-ALPA Switching

Solution Overview

Problem

Existing Fibre Channel Arbitrated Loop (FC-AL) bridge devices fail to provide fair access to all devices on the communication medium, particularly when coupled through a bridge device, as they prioritize the highest T-ALPA value, leading to unfair access opportunities for devices represented by the bridge device.

Innovation Solution

A bridge device equipped with Fibre Channel layer 2 logic and a Loop Port State Machine logic circuit that maintains arbitration information for each T-ALPA, generating signals to ensure all devices associated with the bridge have a chance to arbitrate before the access window closes, thereby providing access fairness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If the bridge device prioritizes the highest T-ALPA value for loop access, then the highest priority device can access the loop quickly, but lower priority devices are blocked from loop access

Engineering Contradiction:

Improveloop access speedVSAvoidaccess fairness

Core Design Contradiction:

SpeedVSEase of operation

Solution Approach 1:

The bridge device dynamically changes its arbitration behavior based on whether it currently holds loop access. When the bridge has loop access, it acts as a high-priority device (lowest T-ALPA). When it releases loop access, it temporarily adopts the identity of the next highest priority device that wants loop access, allowing that device to win arbitration. This dynamic role switching ensures fair access while maintaining efficient arbitration.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The bridge device acts as an intermediary between multiple T-ALPA devices and the FC-AL loop. Instead of allowing direct competition where the highest priority device always wins, the bridge mediates by selectively presenting different T-ALPA values to the arbitration process, ensuring each device gets fair opportunity while maintaining system efficiency.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If multiple target devices are ready to provide responses simultaneously, then system throughput increases, but only one target can access the loop at a time

Engineering Contradiction:

Improvesystem throughputVSAvoidwaiting time

Core Design Contradiction:

ProductivityVSLoss of time

Solution Approach 1:

The bridge device performs preliminary actions by maintaining a queue of T-ALPA values in priority order before arbitration occurs. When loop access becomes available, the bridge has already prepared the appropriate T-ALPA value to present, enabling immediate arbitration without delay. This preliminary preparation allows multiple devices to be ready simultaneously while maintaining orderly access.

Inventive Principle:

Principle #10Preliminary action

3Device complexity

If the bridge device uses a single T-ALPA value for arbitration, then arbitration is simple, but devices coupled through the bridge cannot achieve fair access

Engineering Contradiction:

Improvearbitration complexityVSAvoidaccess fairness

Core Design Contradiction:

Device complexityVSEase of operation

Solution Approach 1:

The bridge device dynamically changes its arbitration behavior based on whether it currently holds loop access. When the bridge has loop access, it acts as a high-priority device (lowest T-ALPA). When it releases loop access, it temporarily adopts the identity of the next highest priority device that wants loop access, allowing that device to win arbitration. This dynamic role switching ensures fair access while maintaining efficient arbitration.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The bridge device adds a temporal dimension to arbitration by using different T-ALPA values at different times within the same access window. Instead of a single static T-ALPA, the bridge switches T-ALPA identities based on arbitration needs, effectively adding a time-based dimension to the arbitration process that enables fair access for multiple devices.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentUS8379665B2Apparatus and methods for access fairness for a multiple target bridge/router in a fibre channel arbitrated loop system

Publication Date: 2013.02.19 AVAGO TECHNOLOGIES INTERNATIONAL SALES PTE LTD

AI summary

Apparatus and methods improved fair access to a Fiber Channel Arbitrated Loop (FC-AL) communication medium through a bridge device. The enhanced bridge device provides for a fair access in a currently open access window for all presently requesting devices coupled through the bridge device to the FC-AL communication medium. Thus all devices on the loop whether coupled directly or through a bridge device can be assured fair access to the loop when there are simultaneous requests during an open access window.