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T568A vs T568B: Choosing the Right Ethernet Wiring Standard

So you‘re setting up a new network and come across a choice: T568A or T568B wiring? What‘s the difference, and how do you pick? This in-depth guide has got you covered!

We‘ll examine:

  • The history behind T568 cabling standards
  • Key wiring differences between T568A and T568B
  • Backward compatibility with older cabling
  • Usage in modern networks
  • Crossover cables to interconnect everything
  • Recommendations for various scenarios

By the end, you‘ll understand T568A and T568B intricately – allowing you to make the best choice when wiring your networks!

Tracing the Origins of T568 Ethernet Cabling

First, a quick primer on T568 standards for twisted-pair copper cabling in ethernet networks:

T568A arose in 1991 from the Telecommunications Industry Association (TIA). It defined a specific wiring scheme for ordering colored wire pairs when terminating cables with RJ45 connectors.

This standard brought consistency for ethernet cabling across the networking industry.

Over the next decade, ethernet speeds increased from 10Mbps to 100Mbps and even 1Gbps over twisted pair cabling. To accommodate higher transmission rates, an updated T568B standard was introduced in 2002 with minor changes to the wiring scheme.

Here‘s a quick timeline:

timeline
    TIA/EIA-568-1991 (T568A) - Initial standard 
    - 2002 - TIA/EIA-568-B (T568B) released
    - 2008 - TIA/EIA 568-A-1 and 568-B-1 - CAT6/6A
    - Current - T568B common for new installs

Now let‘s dive into the key wiring difference between these two standards.

Demystifying the Wiring: T568A vs T568B

At first glance, T568A and T568B appear quite similar – they both define RJ45 pinouts for 4 twisted wire pairs typically colored:

  • Green
  • Orange
  • Blue
  • Brown

But the actual order in which these colored wires get connected differs:

T568A Wiring

Pins   Wire Color
----   ----------
1      White/Green
2      Green
3      White/Orange 
4      Blue  
5      White/Blue
6      Orange
7      White/Brown
8      Brown

T568B Wiring

Pins   Wire Color
----   ----------
1      White/Orange
2      Orange 
3      White/Green
4      Blue
5      White/Blue
6      Green
7      White/Brown
8      Brown

As you can see above, while the overall wire colors stay the same, pairs 2/3 and 6/7 get swapped when going from T568A to T568B!

This simple modification to the first two wire pairs improved compatibility for communication at 1000Base-T Gigabit ethernet speeds.

Now let‘s move on to…

Backward Compatibility with Legacy Cabling

A key benefit of both T568A and T568B wiring is backward compatibility with previous telephony and networking standards:

  • T568A maintains compatibility with USOC terminology for telephone cables
  • T568B remains compatible with AT&T 258A specifications

This means if you come across really old telephone wiring, chances are it will work just fine for ethernet too! Modern ethernet equipment can intelligently adapt based on which wire pairs get detected.

However, as we‘ll see next, T568A and T568B themselves are not natively compatible…

Connecting Disparate T568A and T568B Devices

Here‘s the catch: since T568A and T568B have swapped wire pairs (Orange, Green), you cannot directly connect them without a conversion in between!

Interconnecting T568A and T568B requires a crossover cable, with outputs crossed over like so:

graph TB
    T568A[RJ45<br>T568A] --> |Crossover| Xover((Crossover<br>Cable))
    Xover --> |Crossover| T568B[RJ45<br>T568B]

The good news is these crossover cables are easily constructed using the wire color schemes we just learned.

With such cables, you can seamlessly connect components with all kinds of mismatched brillant cabling!

Now time for the moment you‘ve been waiting for…

Making the Choice: T568A or T568B?

Drumroll please! 🥁

When wiring a brand new network install, the choice is clear – go with T568B.

Here are some great reasons why:

  • T568B is the more modern standard – improved Gigabit compatibility
  • Most off-the-shelf cabling uses T568B termination
  • Following conventions allows for simpler expansion later

Makes sense right? Now for a twist…

If your infrastructure already utilizes older T568A cabling, no need to replace everything!

Simply use crossover cables at junction points between the two standards. This allows legacy T568A segments to coexist happily with newer T568B cabling.

The following flowchart summarizes the decision making process:

flowchart TB

    Start([New wiring?])

    Existing[Must interface<br>with existing<br>T568A equipment?]

    New([Use T568B Standard])

    Crossover[Use T568B with<br>T568A Crossover Cables]

    New ---> End([Done!])

    Start --> |Yes| New

    Start --> |No| Existing

    Existing --> |Yes| Crossover

    Existing --> |No| New

    Crossover ---> End

And there you have it! As you can now see, while T568A and T568B appear confusing at first, the concepts are simple enough with some study.

You‘re now equipped to handle all kinds of ethernet cabling scenarios. Feel free to reach out with any other questions!

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