Switching Network Cell Scheduling for Back Pressure Delay Reduction
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Solution Overview
Problem
In switching network systems, the egress Fabric Interface Chip (FIC) faces limited Input Queue (IQ) resources, leading to increased transmission delays due to back pressure from lower-level nodes, especially during traffic bursts or unbalanced distribution, compromising system stability and performance.
Innovation Solution
An upper-level node in the switching network system shares the sorting load of lower-level nodes by delaying cell transmission based on a sending delay threshold determined by factors such as hop count, transmission delay, and congestion feedback, optimizing resource allocation and reducing back pressure-related delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the egress FIC uses IQ buffer to eliminate delay difference, then packet assembly can be completed, but IQ resources are easily exhausted during traffic bursts
Solution Approach 1:
The ingress FIC performs preliminary distribution of cells to multiple SEs before the egress FIC needs to perform packet assembly. By pre-distributing cells across multiple output queues of different SEs, the system prepares the sorting function in advance, reducing the burden on IQ resources at the egress FIC when actual packet assembly is needed.
2Reliability
If the egress FIC back-pressures the SE when IQ resources are exhausted, then transmission can be controlled, but transmission delays greatly increase due to back pressure transfer time and high RTT
Solution Approach 1:
The sorting function is segmented and distributed across multiple SEs rather than being concentrated at the egress FIC. Each SE handles a portion of the sorting load independently, allowing parallel processing of cells and reducing the need for back-pressure control, thereby minimizing transmission delays.
Solution Approach 2:
Multiple SEs act as intermediaries between the ingress FIC and the egress FIC. These SEs perform local sorting and filtering of cells, mediating the traffic flow and reducing the burden on the egress FIC's IQ resources, which in turn reduces the frequency and impact of back-pressure events.
3Adaptability or versatility
If multiple SEs output cells to the egress FIC, then distribution flexibility is improved, but delay difference between paths increases requiring more IQ buffer
Solution Approach 1:
The system performs preliminary distribution of cells to multiple SEs with different output queues, preparing the sorting function in advance. This pre-distribution strategy allows the system to handle path delay differences without requiring excessive IQ buffer resources at the egress FIC, as the sorting work is already partially completed across multiple SEs.
Data Source
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AI summary
A first aspect of the embodiments of this application provides a communication method. In the method, a first node obtains a target cell and a target moment, where the target moment is used to indicate a moment at which the target cell is processed. In a process in which the first node sends the target cell to the lower-level node in the switching network system, the first node sends the target cell to the lower-level node only when the difference between a system moment of the first node and the target moment is greater than the sending delay threshold. In other words, the first node delays, by using the sending delay threshold, sending the target cell, so that an upper-level node in the switching network system shares sorting load of a lower-level node, to avoid an increased transmission delay caused by back pressure of the lower-level node, optimize sorting resources between different levels of nodes in the switching network system, and improve stability of the switching network system.