Packet Transmission Scheduling Using Measured Path Latency
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Solution Overview
Problem
Network devices operating under the IEEE 802.1Qbv standard face inefficiencies due to variable latency and jitter, leading to unused transmission time and reduced throughput, as they must assume the worst-case latency for packet transmission, which results in underutilization of reserved time slots for time-critical packets.
Innovation Solution
A network device measures the time required for each network interface to transmit packet data through respective transmit data paths and uses this information to determine the optimal timing for packet transfer, ensuring that lower priority packets are completed before time slots reserved for time-critical packets, thereby reducing jitter and improving throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the network device assumes worst-case latency for packet transmission, then the reliability of time slot reservation is improved, but the throughput is reduced due to unused transmission time
Solution Approach 1:
The system performs preliminary measurement of actual transmission times for packet data through transmit data paths and stores these measurements in a lookup table. This preliminary action allows the scheduling control circuitry to retrieve actual transmission time information during packet scheduling, replacing the need to assume worst-case latency and enabling more efficient time slot utilization while maintaining reliability.
2Productivity
If the network device uses measured actual transmission times for scheduling, then the throughput is improved by reducing unused transmission time, but the device complexity increases due to measurement and scheduling control requirements
Solution Approach 1:
The scheduling control circuitry automatically retrieves actual transmission time information from the lookup table based on packet characteristics and transmits data path information, eliminating the need for manual configuration or complex real-time measurement systems. The system self-manages its own scheduling optimization using pre-measured data, reducing operational complexity while maintaining high throughput.
3Reliability
If the network device dequeues packets based on worst-case latency assumptions, then the time slot reservation is safe, but the latency varies causing jitter
Solution Approach 1:
The system measures actual transmission times for packet data and uses this feedback information to update scheduling decisions. The scheduling control circuitry retrieves actual transmission time data from the lookup table and adjusts packet dequeue timing accordingly, creating a feedback loop that reduces latency variation and jitter while maintaining safe time slot reservations through continuous optimization based on real performance data.
Data Source
AI summary
A network device transfers packets from a packet memory to one or more network interfaces for transmission by the one or more network interfaces. The transferring of packets includes transferring the packets via one or more respective transmit data paths that correspond to one or more respective network interfaces. The network device measures one or more respective amounts of time required to transmit respective packet data within the one or more respective transmit data paths. The network device uses the one or more respective measured amounts of time to determine when to start transfer of packets from the packet memory to the one or more network interfaces via the one or more respective transmit data paths.