[ 6 pages—2,861 words]


INTRODUCTION

Selecting the proper Industrial Ethernet switch can be a confusing task. There are many options to consider such as auto-negotiation features, managed versus unmanaged, redundancy, environmental concerns, future-proofing, determinism issues and many more.


What does a switch do?

Before investigating all the features provided by Industrial Ethernet switches, we should first consider exactly what an Ethernet switch is and what it does. An Ethernet switch (also known as a switching hub), basically, interconnects Ethernet devices. It receives frames transmitted by one device and passes these frames onto appropriate switch ports which connect to other Ethernet devices. As it passes these frames it also learns where Ethernet devices are located and uses this information to decide which ports to use for passing frames. This helps cut down on network utilization as frames only go to the appropriate switch ports.

An Ethernet hub (also known as a repeating hub) is a similar device, but it only allows one device at a time to communicate on the entire network. This provides less network efficiency as each device must wait its turn to transmit a frame.

Most Ethernet switches use the store-and-forward method to pass frames. The switch receives an entire frame and then transmits this frame out the appropriate port(s). A repeating hub, however, will receive one bit and re-transmit this bit.

As the switch learns where devices are located, it stores this information in its built-in address table memory. It also has memory for frames it is in the process of forwarding. Each switch will vary in address storage space and frame storage space. One consideration is how many Ethernet devices you will have in your entire network. Your switch should have enough address storage memory for each device in the network. For example, if you plan on having 100 Ethernet devices in your network, your switch should have an address table large enough to store at least 100 Ethernet addresses.

Most switches provide basic functionality for monitoring the network in the way of LEDs for link and activity. Most switches also provide the ability to negotiate some of their settings.

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