Packet Switch Virtual Output Queues with Old Age Indicators
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Solution Overview
Problem
Existing packet switches face performance and throughput issues due to the exponential growth in complexity and decreased speed of logic as the number of input and output ports increases, particularly exacerbated by multicast data packets which experience higher latency and reduced throughput.
Innovation Solution
Implementing a packet switch that uses virtual output queues with an old age indicator to prioritize routing, eliminating the need for timestamps and simplifying logic circuitry, allowing for concurrent routing of multicast data packets and reducing latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the oldest cells first (OCF) algorithm is employed to route data packets through a packet switch, then fairness in routing is improved, but the size and complexity of logic grows exponentially as the number of input ports and output ports increases
Solution Approach 1:
The patent segments the cell selection process into two independent phases: (1) cell gathering phase where cells are collected from input ports based on virtual output queue age, and (2) cell routing phase where selected cells are routed to output ports. This segmentation allows the arbitration logic to operate on simplified age indicators rather than evaluating all possible cell combinations, thereby reducing logic complexity while maintaining fairness.
Solution Approach 2:
The patent transitions from maintaining detailed timestamp information for each cell to using a simplified age indicator for each virtual output queue. This dimensional reduction transforms the complexity from O(N*M) timestamp comparisons to O(N+M) queue age comparisons, where N is the number of input ports and M is the number of output ports, significantly reducing logic complexity while preserving the oldest-cell-first fairness property.
2Reliability
If the oldest cells first (OCF) algorithm is employed to route data packets through a packet switch, then fairness in routing is improved, but the speed of the logic decreases as the size and complexity of the logic increases
Solution Approach 1:
By segmenting the arbitration into gathering and routing phases with distinct selection criteria, the patent enables parallel processing of cell selection decisions. The simplified age-based selection in the gathering phase can be executed faster than detailed timestamp comparisons, improving overall logic speed while maintaining fairness through the structured two-phase approach.
Solution Approach 2:
The patent changes the parameter used for cell selection from detailed timestamp values to simplified age indicators. This parameter transformation reduces the computational burden of comparisons and enables faster logic operation while preserving the relative ordering needed for fairness in the oldest-cell-first algorithm.
3Reliability
If cells of a multicast data packet are individually routed to each destination output port, then complete multicast delivery is achieved, but throughput of the packet switch is reduced
Solution Approach 1:
The patent merges multiple cells of the same multicast packet that are destined for different output ports into a single routing operation. By identifying that multiple virtual output queues contain cells from the same multicast packet and combining their routing decisions, the system achieves complete multicast delivery while reducing the number of individual routing operations, thereby improving throughput.
Solution Approach 2:
The patent extends the cell gathering mechanism to handle multicast packets universally. The same age-based selection logic that works for unicast packets is applied to multicast packets, and the routing phase is enhanced to recognize and batch-route multiple destinations simultaneously. This multi-functional approach maintains delivery completeness while improving efficiency for both unicast and multicast traffic.
4Reliability
If cells of a multicast data packet are individually routed to each destination output port, then complete multicast delivery is achieved, but latency of the multicast data packet is substantially higher than latencies of other data packets
Solution Approach 1:
The patent merges the routing of multiple multicast cells destined for different output ports into a single time slot. By combining the routing operations for all destinations of a multicast packet, the system achieves complete delivery while minimizing the time required, thereby reducing latency compared to sequential individual routing of each cell to each destination.
Solution Approach 2:
The patent performs preliminary identification and grouping of multicast cells during the cell gathering phase, before the actual routing occurs. By pre-identifying which cells belong to the same multicast packet and grouping them together, the system prepares for batch routing, which reduces the overall latency compared to discovering and routing each cell individually during the routing phase.
Data Source
AI summary
A packet switch includes virtual output queues for mapping data units of data packets from input ports to output ports of the packet switch. The packet switch selects virtual output queues based on old age indicators of the virtual output queues and routes data units mapped at heads of the selected virtual output queues to output ports of the packet switch. Further, the packet switch may identify a data unit of a multicast data packet mapped at the head of more than one virtual output queue and contemporaneously route the data unit to more than one output port. Additionally, the packet switch may update an old age indicator to indicate a virtual output queue is old if the virtual output queue maps an unserviceable data unit of a multicast data packet and the same data unit is mapped at the head of a selected virtual output queue.