Module-First Matching for Scalable Clos-Network Switches
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Solution Overview
Problem
The scalability of Clos-network switches is limited by complex configuration processes, high hardware complexity, and the need for large schedulers due to the number of ports, making it difficult to implement high-capacity switches efficiently.
Innovation Solution
The module-first matching (MoM) scheme simplifies the configuration of IQ Clos-network switches by performing matching between first- and third-stage modules first, followed by matching between input and output ports, using a weighted selection scheme based on longest queue occupancy to reduce hardware complexity and enable the use of smaller schedulers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a single-stage switch is used to achieve high capacity, then the switching capacity is improved, but the hardware complexity increases significantly
Solution Approach 1:
The patent divides a large single-stage switch into multiple smaller switching modules arranged in a multi-stage Clos network architecture. Each module handles a portion of the total traffic, reducing the complexity of individual modules while collectively providing high switching capacity. The switch is segmented into input stage modules, middle stage modules, and output stage modules, where each module has fewer crosspoints than a single large switch would require.
2Quantity of substance
If the number of ports N is increased to achieve high capacity, then the switching capacity is improved, but the scheduler size and hardware complexity increase as O(N^2)
Solution Approach 1:
The scheduler is segmented and distributed across multiple switching modules rather than being centralized. Each module has its own local scheduler that handles only the ports assigned to that module. For example, in a 1024-port switch divided into 32 modules of 32 ports each, each scheduler only needs to handle 32×32 matching instead of a single 1024×1024 scheduler, dramatically reducing hardware complexity.
Solution Approach 2:
The patent introduces a modular dimension to the switch architecture, organizing ports and schedulers into hierarchical groups. Instead of a flat N×N scheduler structure, the system uses multiple smaller n×n schedulers arranged in a modular Clos network, where the overall capacity scales with the number of modules rather than requiring a single large scheduler.
3Loss of time
If a fast packet scheduler is used to reduce configuration time, then the configuration speed is improved, but the hardware complexity and implementation difficulty increase
Solution Approach 1:
The configuration process is segmented into independent module-level scheduling operations rather than a single centralized configuration step. Each switching module can be configured independently and in parallel, reducing the overall configuration time while keeping each individual scheduler simple. The arbitration process is divided into module-level arbitration and port-level arbitration, each handled by simple local logic.
Solution Approach 2:
Each switching module performs its own configuration and arbitration independently without requiring complex centralized control. The modules use simple local arbiters that autonomously make scheduling decisions based on local queue states, eliminating the need for a complex global scheduler and reducing both configuration time and implementation complexity.
Data Source
AI summary
A configuration scheme for IQC switches that hierarchizes the matching process reduces configuration complexity by performing routing first and port matching afterwards in a three-stage Clos-network switch. This scheme applies the reduction concept of Clos networks to the matching process. This, in turn, results in a feasible size of schedulers for up to Exabit-capacity switches, an independent configuration of the middle stage modules from port matches, a reduction of the matching communication overhead between different stages, and a release of the switching function to the last-stage modules in a three-stage switch. The switching performance of the proposed approach using weight-based and weightless selection schemes is high under uniform and non-uniform traffic. The number of stages of a Clos-network switch can be reduced to two.