T568a vs T568b, Which to Use

T568a vs T568b, Which to use


Written by Brian Lowery, Senior Network Administrator at Jackson Technical


Data cabling; it can be confusing sometimes. If you are just getting started on your network, or if you need to rewire some things, trying to determine what standard you should use or what type of cable to purchase can be a daunting. Today we are going to help you decide what wiring standard should be adopted. We will assume CAT6 cabling is being used and you need direction on how to wire up your patch cables.

There is a termination standard set by the Telecommunications Industry Association (TIA) indicating how the pinout or pair assignments should be used in cabling. Standard TIA\EIA-568 sets the standard for how to match twisted pair wires to a plug or socket. This is important because if the conductors do not match on each end then the cables will not function.

The T568A and T568B are the termination standards used by Internet backbone infrastructure, Internet providers and all the way down to end user consumers or businesses. The only real difference between these two pin-to-pair assignments are the green and orange pairs. These two sets are swapped in the cable. Even though these are switched, they are still both configured as direct or straight through connections on each end. I believe this is why it’s so confusing to most, because using either of these standards gets the same result; a working patch cable. The T568A standard is the most widely accepted standard because it is backward compatible to most wiring schemes and the one I recommend for most applications.

 

TIA 568A TIA 568B and Cross-over cable diagram

Images credit: Industrial Ethernet Book

 

RJ45 Pinout t-568a

 

In most network applications, the standard cabling method is required. For example, a computer plugged into a wall panel uses the standard cable configured with either T568A or T568B termination. This allows the computer to communicate with other devices on the local area network. Whether talking to a network printer or mail server, the data traverses the network because all the cabling has been put together using one of the above termination standards. The same is true for the cabling in the wall and the patch panel where they all terminate.

Now for other applications, we may need to connect a computer direct to another computer or a host-to-host connection. As an example, we need to copy data from one computer to another, but the two computers don’t have access to a switch for help with this process. These two computers need to use a cross-over cable.

In a standard network, a switch or router is used as an in-between device that can cross the data connections so the receiving computer can use the data. A cross-over cable can be used to accomplish the same task without the need for the in-between hardware. The cross-over cable uses the same cable type, but is terminated differently. The cable uses the T568A termination standard on one end and the T568B standard on the other end. Terminated in this way, the transmit and receive signals are reversed. In most networks, cross-over cables are not needed as they have a specific use.

Cables can be made with either termination standards and in most instances will work. The industry preferred is the T568A because of the backward compatibility it has. In all situations, one standard should be adopted and used to avoid a mixed environment. Then when it comes to the cross-over cable, its only needed in host-to-host situations so those cables are not used often. Today most Ethernet devices have a feature called MDI-X which is an auto detection support to prevent signal conflicts if a cross-over cable is plugged into a switch or router.

In conclusion, use one standard and stick to it for your network purposes and only use a cross-over when needed.

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