Quantum Ethernet remote I/O networks provide deterministic operation when the following principles are incorporated in the network design:
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Defined Architectures: A network topology that consists of simple daisy chain loops, or with , provides the following design advantages:
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Hop counts between the remote adapter device and the controller are limited. The smaller number of hops along the transmission path reduces the opportunity for network delays.
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Junctions between devices in the topology also are limited, which in turn limits packet queuing delays, known as .
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Traffic Prioritization: Jitter that is inherent in remote I/O traffic is further limited by using to prioritize packets. When remote I/O packets and other traffic (e.g., distributed I/O packets, programming commands, web inquiries, diagnostics) simultaneously enter a transmission queue, Ethernet remote I/O traffic is transmitted first, based on its higher priority.
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Switched Ethernet: Switched Ethernet reduces jitter by helping data packet avoid collisions. Switched Ethernet is implemented when you use switches with the following features:
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Store and forward: The switch receives the entire packet before forwarding it, which lets the switch prioritize packet transmissions and check for corrupted packets before re-transmission.
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Full duplex: The switch supports the simultaneous bi-directional transmission of packets, without collisions.
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100 Mbps transmission speeds, which limits delay times per hop, as set forth below.
Switched Ethernet Delay Times
Switched Ethernet topologies can provide for the following transmission delay times per hop:
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I/O Data Size (Bytes)
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Estimated Delay Time (μs)1
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64
|
20
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|
128
|
26
|
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256
|
35
|
|
400
|
46
|
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800
|
78
|
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1200
|
110
|
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1. Delay times include 100Bytes of Ethernet overhead.
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