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FAQ: What is an Auto-sensing Ethernet Port

FAQ: What is an Auto-sensing Ethernet Port

When you’re browsing features and specifications for your networking equipment, you might come across something known as autosensing.

What is it, and why does it matter?

It’s a feature specific to Ethernet devices. It’s pretty common these days, but it is important to have on any network that services multiple endpoint devices, and when you know how it works, it can help you plan out your own network that much better. So, let’s get into it.

A Crash Course in Auto-Sensing Ethernet

What is this all about?

Ethernet ports are capable of automatically sensing the speed of devices connected at the other end. If you read a modern Ethernet device manual, it probably claims to support 10/100 or 10/100/1000 Ethernet connections (although there are variations beyond these options). Those numbers represent speeds in megabits per second (Mbps).

Basically, Ethernet can connect at any of these three speeds. Newer devices can pretty much all connect at 1000 Mbps, but if you have any older or legacy devices, they might run at lower speeds.

An autosensing Ethernet port activates when it is connected. They send a few small signals back and forth across the connection, and that allows them to determine the connection speed of the device on the other end. With this information, the Ethernet device can optimize signal speeds to make the network run better.

Here’s an example to clarify how this works in practice.

Say you have a modern 10/100/1000 switch, and it services 2 different devices. One is a modern PC with a 1000 Mbps Ethernet port. The other is an old network-enabled security camera that only runs at 10 Mbps. In theory, your switch could send signals to both devices at its own maximum speed, but that would require a bandwidth of 2000 Mbps (or 2 Gbps).

Conversely, the switch could throttle the connection speed to the camera down to 10 Mbps and connect to the PC as fast as possible. By doing this, the switch is conserving total bandwidth to make the whole network more efficient.

As you expand the network, this efficient throttling matters more and more, especially once the networking capabilities of all of the connected devices start to exceed your total bandwidth.

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