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Fine-Grain Time Division Multiplexing of Ethernet

Fine-Grain Time Division Multiplexing of Ethernet Providing Time-Bounded Message Delivery Using KURT-Linux. Distributed Real-Time Embedded (DRE) systems require networks spanning multiple machines Predictable message delivery latency required

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Fine-Grain Time Division Multiplexing of Ethernet

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  1. Fine-Grain Time Division Multiplexing of Ethernet Providing Time-Bounded Message Delivery Using KURT-Linux • Distributed Real-Time Embedded (DRE) systems require networks spanning multiple machines • Predictable message delivery latency required for reliable end-to-end computation scheduling • However Ethernet is based on random message transmission and collision detection (CSMA/CD) • Collisions and exponential back-off cause random and highly variable packet delays • Linux use of Ethernet is thus not suitable for DRE systems because of unpredictability • Make Ethernet suitable for modest scale DRE systems by providing collision free TDM-Ethernet • Provide predictable end-to-end packet delivery delays as core of network QoS support • Use KURT-Linux (1) Group Scheduling (GS) precise control of network protocol component execution, (2) low interrupt response latency, and (3) fine-grain clock synchronization • Transmit QoS uses precision (~30 msec) of 1 & 3 • Receive QoS uses precision (~30 msec) of 1 & 2 Implementation Details • KURT-Linux TDM-Ethernet creation required: • Refactoring of transmit and receive soft-IRQs • GS control of soft-IRQs and hard-IRQs • KURT-Linux QoS traffic control policy creation • TDM scheduling service creation • No modifications of protocols (UDP/TCP/IP) • Pure software solution uses COTS hardware • Approach appropriate for DRE systems where • ~500 msec TDM slots per machine are acceptable • E.g. ~10 machines on single Ethernet switch • Good driving problem for KURT-Linux and GS Project Goals Ethernet Predictability Problem Proposed Solution Experiment Results • Data Stream visualization of TDM • slots for a three machine test • Hundreds of megabytes were • transferred without packet loss • Desired end-to-end QoS between • applications was provided across • COTS Switched Ethernet • Analysis shows 300 msec transmit bound for 1.5 KB packets on a 500 MHz Pentium (KURT-Linux) over 100 Mb/s switched Ethernet - 500 msec TDM slots per machine provide a comfortable margin 040405

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