Overview

M580 Ethernet RIO networks provide deterministic operation when the following principles are incorporated in the network design:

  • Defined Architectures: A network topology that consists of simple daisy chain loops provides these design advantages:

    • 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.

    • Junctions between devices in the topology also are limited, which in turn limits packet queuing delays, known as jitter.

  • Traffic Prioritization: Jitter that is inherent in RIO traffic is further limited by using QoS to prioritize packets. When RIO packets and other traffic (e.g., DIO packets, programming commands, web inquiries, diagnostics) simultaneously enter a transmission queue, Ethernet RIO traffic is transmitted first, based on its higher priority.

  • Switched Ethernet: Switched Ethernet reduces jitter by helping data packets avoid collisions. Switched Ethernet is implemented when you use switches with the following features:

    • 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.

    • Full duplex: The switch supports the simultaneous bi-directional transmission of packets, without collisions.

    • 100 Mbps transmission speeds, which limits delay times per hop, as set forth below.

Switched Ethernet Delay Times

Switched Ethernet topologies can provide for these transmission delay times per hop:

I/O Data Size (bytes)

Estimated Delay Time (μs)1

128

26

256

35

400

46

800

78

1200

110

1400

127

1. Delay times include 100 bytes of Ethernet overhead.