WCMP Flow Distribution for Asymmetric Multi-Stage Networks
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Solution Overview
Problem
Multi-stage networks with uneven connectivity between stages face challenges in evenly distributing traffic, leading to oversubscription and congestion due to the inability to utilize all uplink ports efficiently, especially when the number of links does not evenly divide among switches, causing issues with Equal Cost Multi Path (ECMP) flow distribution.
Innovation Solution
Implementing Weighted Cost Multi Path (WCMP) flow distribution by assigning weights to links based on their bandwidth, allowing for uneven distribution of traffic to fully utilize all uplink ports and prevent oversubscription, using a method that determines the percentage of packets to transmit through each connection based on the bandwidths of different links, thereby optimizing load balancing and reducing packet loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If Equal Cost Multi Path (ECMP) flow distribution is used to distribute traffic evenly among all egress ports, then traffic distribution simplicity is improved, but network resource utilization deteriorates due to inability to handle uneven connectivity
Solution Approach 1:
The patent changes the cost parameter from uniform (ECMP) to variable (WCMP) based on actual path characteristics. Each path is assigned a cost inversely proportional to its bandwidth capacity, allowing the routing algorithm to prefer higher-capacity paths while still distributing traffic across multiple paths, thus improving both resource utilization and maintaining distribution simplicity.
Solution Approach 2:
The patent introduces asymmetric cost values for different egress ports based on their actual connectivity and bandwidth capabilities. Instead of treating all paths symmetrically with equal cost, the system assigns different costs reflecting the asymmetric nature of network connectivity, enabling more efficient traffic distribution matched to actual path capacities.
2Manufacturing precision
If traffic is distributed evenly among all viable egress ports using hash function, then flow distribution uniformity is improved, but port utilization efficiency deteriorates when links have unequal bandwidth
Solution Approach 1:
The patent modifies the distribution parameter from uniform hashing to weighted distribution based on path costs. The hash function still provides uniform distribution characteristics, but the selection of which hash bucket maps to which egress port is guided by cost values, creating a weighted distribution that maintains uniformity while optimizing for port utilization efficiency.
3Productivity
If Weighted Cost Multi Path (WCMP) flow distribution is implemented by assigning different costs to paths based on bandwidth, then network throughput is improved, but routing complexity increases
Solution Approach 1:
The patent introduces a cost parameter that changes based on path bandwidth characteristics. This single parameter change enables the routing algorithm to automatically adapt to varying path capacities without requiring complex multi-dimensional decision logic, thus improving throughput while limiting the increase in routing complexity to a manageable single-parameter adjustment.
4Productivity
If all uplink ports are to be fully utilized in multi-stage networks with uneven connectivity, then network capacity is improved, but traffic distribution complexity increases due to unequal link divisions
Solution Approach 1:
The patent embraces the asymmetric nature of uneven connectivity by assigning different costs to different egress ports. This asymmetric cost assignment naturally guides traffic distribution to match the underlying asymmetric connectivity, allowing full utilization of all uplink ports without requiring complex artificial balancing mechanisms.
Data Source
AI summary
The present technology considers multi-stage network topologies where it is not possible to evenly stripe uplinks from a lower stage of the network topology to switching units in an upper stage of the topology. This technology proposes techniques to both improve overall throughput and to deliver uniform performance to all end hosts with uneven connectivity among the different stages while delivering uniform performance to all hosts. To achieve improved network performance in case of asymmetric connectivity, more flows may be sent to some egress ports than to others, thus weighting some ports more than others, resulting in Weighted Cost Multi Path (WCMP) flow distribution.