Ingress Rate Limiting for Egress Congestion in FC SANs

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Solution Overview

Problem

Egress congestion in Fibre Channel (FC) and Fibre Channel Over Ethernet (FCoE) Storage Area Networks (SANs) occurs due to inappropriate data transmission rates, leading to queued or throttled data and network congestion, which existing methods like data dropping or congestion isolation can be disruptive and inefficient.

Innovation Solution

A network device monitors indications of egress congestion at its ports, such as latency and transmission rates, and limits the ingress rate to prevent congestion by adjusting the data transmission rates, thereby reducing egress congestion and network congestion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If data transmission rate is increased to improve productivity, then data throughput is improved, but egress congestion occurs leading to data queuing and network instability

Engineering Contradiction:

Improvedata throughputVSAvoidnetwork stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The network device monitors egress congestion conditions in real-time and uses this feedback to dynamically adjust the ingress data transmission rate. When egress congestion is detected, the device reduces the ingress rate to prevent queue overflow, and when congestion subsides, it restores the rate to maintain productivity. This closed-loop control resolves the contradiction by continuously adapting transmission rates to current network conditions.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent implements dynamic rate adjustment where the ingress data transmission rate is not fixed but changes based on real-time egress congestion conditions. The system transitions between different transmission states (normal rate, reduced rate, throttled) based on monitored congestion indicators, making the network adaptable to varying load conditions and preventing congestion-related failures.

Inventive Principle:

Principle #15Dynamics

2Reliability

If existing methods like data dropping or congestion isolation are used to handle egress congestion, then congestion is managed, but network disruptions and data loss occur

Engineering Contradiction:

Improvecongestion managementVSAvoiddata loss and network disruptions

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

Instead of reacting to congestion after it occurs, the system proactively monitors egress queue conditions and adjusts the ingress rate before congestion fully develops. By detecting early signs of congestion and preemptively reducing the ingress rate, the system prevents queue overflow and eliminates the need for disruptive data dropping or congestion isolation actions.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent converts the potentially harmful effect of egress congestion into a useful signal for rate adjustment. Rather than allowing congestion to cause data loss and then reacting with disruptive measures, the system uses congestion indicators as feedback to smoothly adjust ingress rates, transforming a harmful condition into a beneficial control mechanism that prevents data loss entirely.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS10992580B2Ingress rate limiting in order to reduce or prevent egress congestion

Publication Date: 2021.04.27 CISCO TECHNOLOGY INC

AI summary

A method performed by a network device comprises egressing data from a port of the network device at an egress rate over a link connected to the port, ingressing data into the port at an ingress rate over the link, monitoring at least one indication with respect to the egressing data in order to determine whether the at least one indication is indicative of egress congestion at the port of the network device, and upon determining that the at least one indication is indicative of the egress congestion at the port, limiting the rate of ingress via the port.