Ethernet cable, as one of the most popular types of networking cable, is mainly utilized to interconnect two wired network devices in the home or the office. Cat 5/cat6, UTP/STP cables are some of this cable type that connects all devices to get a network up and running smoothly. Unlike the fiber jumper, this Ethernet copper cable is usually terminated with a 8P8C modular connector, which is often called RJ45 (Registered Jack). The way the RJ45 connector wired to Cat 5, 5e and 6 cables differs depending upon the type of cable required.
It is known to all that, inside the Ethernet cable, there are eight color coded wires twisted into 4 pairs of wires, which poses difficulty in effectively wiring them. So how to terminated RJ45 connectors at the end of the network cable? In fact, there are three wiring standards available on the market—straight-through cables, crossover cables and rollover cables. In order to have a better understanding of the RJ45 pinout, this article will provide some basic information about them.
Different Wiring Standards
Before starting with the discussion of cable pinout for modular jack, we often get questions as to the difference in straight-through, crossover, and rollover wiring of cables and the intended use for each type of cable. These terms describe the way the cables are wired (which pin on one end is connected to which pin on the other end). The following part shows the exact pinout schemes of the three cables.
- Straight-Through Cables
For this type of cable, the wiring of both ends is the same, in other words Pin 1 connector A goes to Pin 1 on connector B, Pin 2 to Pin 2 etc. Straight-through wired cables are most commonly used to connect a host to client. When we talk about cat 5e patch cables, the straight-through wired cat5e patch cable is used to connect computers, printers and other network client devices to the router switch or hub. Straight-through cable can be either terminated with T568A or T568B standard, just as you can see in the below image.
- Crossover Cables
Crossover cables are very much like Straight-Through cables with the exception that TX and RX lines are crossed (they are at opposite positions on either end of the cable), that’s it, Pin 1 on connector A goes to Pin 3 on connector B. Pin 2 on connector A goes to Pin 6 on connector B, etc. Crossover cable are usually terminated with one end with T568A and the other end with T568B standard This means that two similar devices can communicate with each other, so this is how to connect two computers or two switches or hubs to each other. Crossover cables are most commonly used to connect two hosts directly. Examples would be connecting a computer directly to another computer, connecting a switch directly to another switch, or connecting a router to a router.
- Rollover Cables
A rollover cable as the names implies, refers to the one where the pinouts are reversed. Pin 1 becomes pin 8 and pin 2 becomes pin 7. This type of cable is not used in computer networks, except in very special applications. Rollover cables, sometimes referred to as host cables are most commonly used to connect to a devices console port to make programming changes to the device. Unlike crossover and straight-wired cables, rollover cables are not intended to carry data but instead create an interface with the device.
Cabling Standards—T568A and T568B
Ethernet cables are twisted into 4 wires coded with different colors. The four colors used on Cat 5 and 6 cables are green, orange, blue and brown. One wire in each pair has a solid color and the other has a white stripe added. The telecommunication industry has two standards for cable RJ45 pinouts: T568A and T568B. These standards determine how each of the four pairs of colored wires is connected on the RJ45 connector.
When visually comparing the T568A and T568B wiring configurations side-by-side, you will see that that the pin positions for the green and orange pairs are swapped. On T586A cables, pin 1 is white-green and pin 2 green, whereas on T586B cables, pin 1 is white-orange and pin 2 orange. The difference continues in that pins 3 and 6 are used for the other color. With both standards, the blue pair is always on pins 4 and 5 and the brown pair on pins 7 and 8. T586B is the most common, although the government often uses T586A. The choice is irrelevant provided all components follow the same standard.
How to Configure Ethernet Cable for T568A or T568B
T568A and T568B standards were recognized by ANSI, TIA and EIA. The first is the T568A wiring standard and the second is T568B. Nowadays T568B has surpassed 568A and is seen as the default wiring scheme for twisted pair structured cabling. But this cannot be the unique standard to determine which one is suitable than the other. In fact, whether to choose one standard over the other really depends upon the configuration of the existing network you are working on or if you are building a network from the ground up. The benefit to using the more popular T568B wiring scheme is that it is backward compatible to USOC wiring schemes, but it also accommodates current and future demands on the network.
If you are working on an existing network, it is important to continue with the existing wiring scheme for straight through cables. If this is unknown, this can be determined by testing the cables for continuity. Mixing the two schemes will prevent data signals from transferring simply because the individual colored and striped wires will not be matching up when you connect the plugs and jacks. Or in some circumstance, it may be necessary to mix the two configurations when previously T568A-wired components will be connected to T568B components. In this case, you would want to create a crossover cable by terminating one end with a T568A terminated plug and the other with a T568B plug to prevent data loss.
Conclusion
The RJ45 pinout standards specify two wiring schemes on how to configure RJ45 Ethernet cable. While the T568A and T568B wiring standards are very similar, the T568B scheme is more commonly used for many data cable applications. Note that whether to use T568A or T568B really depends on the existing wiring, jacks or personal preference, and you should take consistency into account as well. FS.COM provides a full range of optical devices, including the Ethernet cables, fiber optic cables, optical transceivers, DAC/AOC and so on. Custom fiber patch cords are also offered.
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