Upstream Network Device VoQ Congestion Avoidance
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Solution Overview
Problem
In network devices, congestion at one egress port can lead to unnecessary reduction in packet transmission rates across all egress ports, even if other ports are not congested, resulting in inefficient use of network links and potential packet loss.
Innovation Solution
Implementing virtual output queues (VoQs) in upstream network devices to independently manage packet flow to specific congested egress ports, based on forwarding information and congestion monitoring by downstream devices, allowing for targeted reduction in packet flow only to congested ports without affecting non-congested ports.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flow control messages cause upstream network device to modulate flow of all packets to downstream network device, then congestion at downstream network device is alleviated, but transmission rate of packets to non-congested egress ports is unnecessarily reduced
Solution Approach 1:
The patent segments the packet flow into separate virtual output queues (VOQs), with each queue corresponding to a specific egress port of the downstream network device. This segmentation allows the upstream network device to independently control packet flow to each egress port, applying flow control only to queues corresponding to congested ports while maintaining full transmission rates to non-congested ports, thus resolving the contradiction between congestion avoidance and maintaining productivity.
Solution Approach 2:
The patent implements local quality control by associating each virtual output queue with a specific egress port and applying flow control measures selectively to individual queues based on the congestion status of their corresponding ports. This localized approach ensures that flow control actions are applied only where needed (congested ports) while leaving other ports operating at full capacity, thereby avoiding unnecessary reduction in overall packet transmission rate.
2Reliability
If flow control is applied to all packets, then congestion at downstream network device is prevented, but network link efficiency is reduced
Solution Approach 1:
The patent segments packet flows into separate virtual output queues corresponding to different egress ports, enabling selective application of flow control only to queues destined for congested ports. This segmentation prevents unnecessary flow control modulation on packets destined for non-congested ports, thereby maintaining network link efficiency while still preventing congestion at affected ports.
Solution Approach 2:
The patent applies flow control measures locally to specific virtual output queues based on the congestion status of their corresponding egress ports. By monitoring congestion at each port individually and applying flow control only where needed, the system prevents congestion effectively while minimizing the impact on overall network link efficiency, as non-congested ports continue to transmit packets at full rate.
3Adaptability or versatility
If virtual output queues are implemented for each egress port, then targeted flow control is achieved, but device complexity increases
Solution Approach 1:
The patent implements a universal virtual output queue structure where each upstream port has a set of VOQs that can serve multiple downstream egress ports. This multi-functional queue structure allows the same queue management mechanisms to handle traffic to different destinations, reducing the need for completely separate queue structures for each port pair and thereby limiting the increase in device complexity while still enabling targeted flow control.
Solution Approach 2:
The patent performs preliminary actions by pre-establishing virtual output queues associated with each downstream egress port before congestion occurs. By having the queue structure ready in advance and pre-configuring the associations between upstream ports and downstream egress ports, the system avoids the complexity of dynamically creating and managing queues during congestion events, thereby reducing overall system complexity while maintaining adaptability.
Data Source
AI summary
An upstream network device in a switching system processes packets an determines respective one or more egress ports of a downstream network device via which the packets are to be subsequently transmitted by the downstream network device. The upstream network device temporarily stores the packets in respective virtual output queues (VoQs) corresponding to the determined egress ports of the downstream network device. Responsively to receiving a flow control message indicating that particular one or more egress ports of the downstream network device are congested, the upstream network device modulates a flow of packets from particular one or more VoQs corresponding to the one or more particular congested egress ports of the downstream network device, to reduce congestion at the particular congested egress ports of the downstream network device, without modulating the flow of packets from other one or more VoQs corresponding to other egress ports of the downstream network device.