Crossbar Scheduler Dynamic Mapping for Buffer Oversubscription
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Solution Overview
Problem
Network elements with crossbar fabrics face throughput degradation due to oversubscription of buffers, where the required rate of packet transmission exceeds the maximum supported rate, leading to incomplete fulfillment of transmission requests.
Innovation Solution
A scheduler dynamically modifies the cyclic mapping between time slots and output ports to reduce the required readout rate from oversubscribed buffers by selecting an alternative group of output ports and applying a permutation that ensures no other buffer becomes oversubscribed, thereby optimizing resource utilization and improving throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a cyclic mapping between time slots and output ports is used for packet transmission, then scheduling simplicity is improved, but buffer oversubscription occurs when required readout rate exceeds maximum supported rate
Solution Approach 1:
The patent applies dynamics by making the cyclic mapping configurable and modifiable. The scheduler can dynamically adjust the mapping between time slots and output ports based on buffer status, transforming a static scheduling approach into a dynamic one that adapts to changing traffic conditions and prevents buffer oversubscription.
Solution Approach 2:
The patent changes the parameter of the cyclic mapping configuration to resolve buffer oversubscription. By modifying which output ports are assigned to which time slots for specific buffers, the system adjusts the readout rate parameters to match buffer capabilities while maintaining scheduling structure.
2Reliability
If the cyclic mapping is modified to resolve buffer oversubscription, then transmission request fulfillment is improved, but scheduling complexity increases
Solution Approach 1:
The patent implements feedback by monitoring buffer status and using this information to guide mapping modifications. The scheduler observes which buffers are oversubscribed and adjusts the cyclic mapping accordingly, creating a closed-loop control system that resolves conflicts while maintaining overall scheduling simplicity through rule-based decision making.
3Productivity
If multiple buffers are simultaneously served in a time slot, then throughput is improved, but buffer oversubscription occurs when readout rate exceeds maximum supported rate
Solution Approach 1:
The patent applies local quality by allowing different buffers to have different cyclic mapping configurations tailored to their specific readout capabilities. Instead of a uniform mapping for all buffers, the system customizes the time slot to output port assignments for each buffer based on its maximum supported readout rate, enabling high throughput for capable buffers while protecting vulnerable ones from oversubscription.
Data Source
AI summary
A network element includes output ports, a crossbar fabric and a scheduler. The output ports are organized in groups of multiple output ports selectable over predefined time slots in accordance with a cyclic mapping assigned to each group. In each time slot, the crossbar fabric routes to fabric outputs data received from the buffers via fabric inputs, in accordance with a routing plan. The scheduler determines and applies the routing plan for transmitting packets from the buffers to the communication network via the crossbar fabric and output ports. When in a given time slot, a required readout rate from a given buffer exceeds a maximum rate, the scheduler selects a group of the output ports to which the given buffer is routed in that time slot, and modifies the cyclic mapping for that group to reduce the required readout rate from the given buffer in the given time slot.