What Is Rj45 Connector In Computer Networking

RJ45 cable plug


RJ45 is a type of connector commonly used for Ethernet networking. It looks similar to a telephone jack, but is slightly wider. Since Ethernet cables have an RJ45 connector on each end, Ethernet cables are sometimes also called RJ45 cables.

The “RJ” in RJ45 stands for “registered jack,” since it is a standardized networking interface. The “45” simply refers to the number of the interface standard. Each RJ45 connector has eight pins, which means an RJ45 cable contains eight separate wires. If you look closely at the end of an Ethernet cable, you can actually see the eight wires, which are each a different color. Four of them are solid colors, while the other four are striped.

RJ45 cables can be wired in two different ways. One version is called T-568A and the other is T-568B. These wiring standards are listed below:

RJ45 or 8P8C connector? If you’re at all involved in computer networking, you have undoubtedly heard both terms used interchangeably when referring to the connectors on the end of your Ethernet cables. But are the terms actually interchangeable, and if they are not, how did this incredibly common practice come to be? That’s what we’ll explore today.

Origins of RJ45

Let’s start with RJ45, perhaps the term most widely used to refer to Ethernet cables today. RJ stands for “registered jack,” and the true RJ 45 connector was originally developed as part of the standardized telecommunication network interface for the purpose of connecting telephone networks. The connectors of the RJ platform were developed as much smaller and cheaper replacements to the older telephone installation methods of hardwired cords or bulky plugs.

With the advent of computer networking, a new but very similar connector was developed to carry out data transfer: 8P8C.

T-568AWhite/Green (Receive +)Green (Receive -)White/Orange (Transmit +)BlueWhite/BlueOrange (Transmit -)White/BrownBrown T-568BWhite/Orange (Transmit +)Orange (Transmit -)White/Green (Receive +)BlueWhite/BlueGreen (Receive -)White/BrownBrown


What is RJ45 connector used for?

An 8-pin/8-position plug or jack is commonly used to connect computers onto Ethernet-based local area networks (LAN). Two wiring schemes–T568A and T568B–are used to terminate the twisted-pair cable onto the connector interface.

How does a RJ45 connector work?

RJ45 plugs feature eight pins to which the wire strands of a cable interface electrically. Each plug has eight locations spaced about 1 mm apart into which individual wires are inserted using special cable crimping tools. The industry calls this type of connector 8P8C, shorthand for eight position, eight contact.

Wiring Pinouts of RJ45 Connectors

Two standard RJ45 pinouts define the arrangement of the individual eight wires needed when attaching connectors to a cable: the T568A and T568B standards. Both follow a convention of coating individual wires in one of five colors (brown, green, orange, blue, or white) with certain stripe and solid combinations.

Following either the T568A or T568B convention is essential when you build your own cables to ensure electrical compatibility with other equipment. If you don’t build your own cables, you only need to verify the correct standard for use with your equipment. For historical reasons, T568B is the more popular standard, although some homes use the T568A version. The table below summarizes this color coding of the wires in the connectors.

Pin T568B T568A
1 white with orange stripe white with green stripe
2 orange green
3 white with green stripe white with orange stripe
4 blue blue
5 white with blue stripe white with blue stripe
6 green orange
7 white with brown stripe white with brown stripe
8 brown brown

Several other kinds of connectors closely resemble RJ45, and they can be easily confused with one another. The RJ11 connectors used with telephone cables, for example, use six-position connectors rather than eight position connectors, making them slightly narrower than RJ45 connectors. Other than that, they look very much the same. 

8P8C Anaysis

8P8C refers to the array of pins, hence the name Eight Position, Eight Contact. In 8P8C connectors, each plug has eight positions that are spaced approximately 1 mm apart. Individual wires are then inserted into these positions. There are a variety of 8P8C connectors out there, with the modern RJ45 Ethernet connector being the most prevalent.

As a result of the close similarities, “RJ45” became the designated informal misnomer for any eight-pinned jack (8P8C modular connector) used in computer networking (Ethernet).

The differences between 8P8C connectors and RJ45 connectors are shown in the following diagram:

0517 RJ45 Image 1

The connectors are not entirely compatible with one another because of the keying used in RJ45; 8P8C connectors can plug into RJ45 receptacles, but the inverse is not true. However, because the connectors resemble each other so closely in appearance, the groups and individuals who transitioned from telephone networking to computer networking started to mistakenly call the unkeyed 8P8C connectors “RJ45s” and the terminology quickly caught on.

Therefore, what most of the industry refers to as RJ45 connectors are in fact 8P8C modular connectors.

Today, almost all electronic equipment using 8P8C connectors will show documentation for RJ45 connectors, which is technically incorrect. This mistaken use of terminology is widespread throughout the industry, and though it is unlikely to change anytime soon, there really isn’t much reason for concern; nearly everyone is collectively making the same mistake, and those who are in the know more often than not simply use RJ45 to avoid confusion or argument.

An example of this is clearly visible in the “RJ45” Ethernet connectors. There are two RJ45 pinouts (T568A and T568B), and even though they are technically 8P8C connectors, it is very likely you will hear them strictly referred to as RJ45 connectors, and all documentation surrounding them will use the same terminology. As such, for the sake of clarity, we will refer to them as modern RJ45 connectors.

Now, the T568A and T568B pinouts mentioned above define the arrangement of the eight individual wires in the connector. These wiring layouts each have their own color convention, and following the convention is important to ensure electrical compatibility. Over time, T568B has become more popular. The differences in color conventions are shown in the chart below.

Wiring Pinouts of RJ45, T568A and T568B Connectors

T568A and T568B wiring pinouts of RJ45 connectors. 

Few people are aware of the important distinctions between RJ45 and 8P8C, but understanding the history of these two connectors and how they formed the backbone for Ethernet connectivity will be integral to recognizing what the next widespread connectivity trend looks like.

Want to know more about current connector trends? These articles can help.

What is difference between RJ11 and Rj12?The difference between Rj11 and Rj12 is that Rj11 is a connection jack that creates a bridged connection for single telephone line which uses flat stain cable for household wire telephone and modem connections, while Rj12 is a connection jack that enjoins central telephone system with single telephone lines through

Issues With RJ45s

RJ45 connectors come with some problems. To form a tight connection between the plug and the network port, some RJ45 plugs make use of a small, bendable piece of plastic called a tab. The tab creates a tighter seal between a cable and a port on insertion, requiring downward pressure on the tab to unplug it. The tab prevents a cable from accidentally coming loose. These tabs easily break when bent backward, which happens when the connector snags on another cable, clothing, or other nearby objects.

Most RJ45 connector problems occur when the wires don’t follow the prescribed standard. People who prefer to work on their own cables and connectors must pay close attention to the proper wiring sequence to avoid problems. 

The Benefits of RJ45 Connectors Explained

When you plug a network device into a local area network, or LAN, it is highly likely that you will be doing so with an RJ 45 Jack Although some networks rely on other types of connectors, such as BNC, RJ45s are now the norm in the majority of Australian offices and homes. One of the chief advantages of an RJ45 connector is that it is easy to plug in and remove with no specialist IT skills being required. A  clip or lug on the back of the jack simply folds down when the connection is made and then sits up holding the jack firmly in place. Conversely, when an RJ45 jack needs to be removed all you need to do is to push the lug down and the entire connector will slide out easily. This approach in the design of an RJ45 makes them extremely versatile. They can be plugged in multiple times without degradation making them ideal for both patch bays and structured data cabling environments. What are their other benefits in an increasingly wireless world?


Although RJ45 jacks were originally designed to offer a great deal of functionality for all sorts of purposes, they are now most commonly used for 10/100 Ethernet connections. Faster than Wi-Fi, nearly all modern Ethernet-enabled computing equipment made today has an RJ45 port in it. The network interface card of a tower PC will provide one or more of them. They are often integrated into the motherboard of smaller devices, such as laptop computers. Because peripheral devices, like scanners and printers, can also be plugged into a LAN using the same connection type, the use of patch cables with RJ45 jacks at either end becomes incredibly convenient. This is simply due to the fact that every device has the same compatibility.

Extra Protection Unlike other connector systems, RJ45 jacks can be offered additional protection which makes the system good even in harsh environments. Where a network is required in an industrial rather than an office setting, RJ45s with tension-resisting boots can be used, protecting the pins of the jack from stress. These reinforced RJ45s also often come with plastic hoods which protect the lug – ideal where cables need to be patched, removed and re-patched on multiple occasions.

Telephony and Data Communications

In places where a LAN is running alongside a telephone system, structured cabling that uses RJ45 connectors is a highly versatile choice. It means both computer equipment and telephones can utilise the same system and be interchanged at will. All sorts of telephony equipment – from business system keyphones to  facsimilr machines– will work well with these standardised connectors.

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