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Standard Ethernet RJ45 vs Keyed RJ45 Connectors

Standard Ethernet RJ45 vs Keyed RJ45 Connectors

If you’ve been in the networking game for a while, or if you work with legacy systems, you may have come across keyed RJ45 at some point. This is a type of Ethernet connector from older systems, but it still works in the modern world when you come across it.

In order to make everything work correctly, though, you’ll need to know a couple of things. So, here’s a crash course in RJ45 connectors.

What Is Standard Ethernet?

Answering this question requires a brief history lesson. After all, Ethernet has been around for multiple decades, and while it still operates on the same principles, the details have changed over time.

The first form of Ethernet was invented in 1973. At the time, Xerox Corporation designed it to work with existing phone communication technology. As a result, it adopted the same plug factor as phones of the time.

Eventually, Ethernet adopted communication techniques that exceeded wired phone connection, and as a result, it required different connectors to accommodate those changes.

Modern Gigabit (or faster ) Ethernet uses more contact points in order to efficiently communicate over eight twisted pairs (whereas phone lines often use two twisted pairs).

This difference is expressed in the modern Ethernet jack style called 8P8C. That refers to 8 positions and 8 contact points in the wire connector.

Now, you may have heard that modern Ethernet uses RJ45 connectors, but this isn’t quite right. RJ45 actually refers to the old phone connectors, and they aren’t quite identical to modern 8P8C connectors. We’ll get into those differences in a bit, but the key to note is that modern Ethernet connectors use the 8P8C configuration. That’s the essential point.

What Is Keyed RJ45?

Building on what you just learned, keyed RJ45 refers to the original RJ45 jacks used by Ethernet back in the 70s (and for some time after). These jacks used a 2P2C configuration, as they had far fewer twisted copper pairs in the communication line.

The original Ethernet connectors simply followed this design, but as Ethernet evolved into the eight-pair design we all know today, the connectors had to adjust as well.

Even though the connectors moved away from the original RJ45 design, the name stayed, and modern Ethernet connectors are still often referred to as RJ45.

Through that journey, the keyed design emerged. This was an early design that enabled 8P8C connectors, but it was intended to still communicate through phone lines. As a result, the connector hybridized modern (at the time) Ethernet with traditional phone lines. In order to do that, the Ethernet connectors needed an extra tab in the plastic to hold them in place in phone jacks. That tab is the “key” in the name.

Understanding the Essential Differences

Let’s put this all together.

Older versions of Ethernet connectors followed the RJ45 design but still provided 8P8C connections. They needed an extra tab in order to fit properly into jacks at the time.

As internet and networking connections moved into the broadband era, phone connections fell out of date, and Ethernet engineers were free to improve on designs. While they stuck with 8P8C configurations, they removed the tab to make an easier, more universal fit across different pieces of networking equipment.

The bottom line is that the only meaningful difference between Ethernet RJ45 and keyed RJ45 is the plastic tab in the connector.

These days, you’re very unlikely to come across a keyed boot design. It was phased out decades ago, but if you somehow do find yourself with such a boot, you’ll find that it doesn’t fit into modern Ethernet ports. The tab gets in the way.

Meanwhile, keyed RJ45 ports are also rare, but very slightly more common than the boots. Some old network systems will keep the old ports because they still work. Keyed RJ45 jacks can receive modern RJ45 boots. The problem only occurs when you plug the old design into new ports — not vice versa. 

What Should You Get?

Unless your equipment or ports predate modern broadband, you’re probably not dealing with keyed RJ45 at all. If you do have legacy systems that might have keyed connectors or ports, then it’s worth paying attention. 

The keyed ports are fine and will work with modern cables. You don’t have to do anything special.

If you find yourself with a keyed boot that you can’t use with your modern equipment, replace the boot. In fact, consider replacing the cable as its age presents performance liabilities.

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