Ethernet MHz Speed: Does It Make a Difference?

Ethernet MHz Speed: Does It Make a Difference?

Written by Don Schultz, trueCABLE Technical Sales Representative & Fluke Networks Certified Technician

Frequently, the “MHz” speed rating of an Ethernet cable is an important checkbox for many shoppers. What exactly does this mean to your network? Does higher MHz speed matter when it comes to Ethernet cable and it’s Category? Does this equate to higher bandwidth? The answer is not a simple yes or no, as you likely have guessed by now. Let’s pump the brakes for a moment and start defining what some of these terms really mean. Then we will put this in a real-world situation so that everyone can make sense of it.

MHz or Megahertz Defined

  • Megahertz is abbreviated as MHz
  • Megahertz is a clock speed measurement of how fast something can go
  • Megahertz, for the curious, is an electrical frequency (take note on the electrical part)

How do you visualize this? Think of MHz as the width of a water pipe. The wider the pipe, the more water it can handle.

Category Defined

  • Ethernet Category (referred to as Cat) is the specific standard used by manufacturers when constructing Ethernet cable. It defines how a category of cable should perform over a defined maximum distance.
  • In the case of the United States, ANSI/TIA loosely defines the physical cable construction standard and strongly defines the electrical performance part of the standard--the latest being ANSI/TIA 568 2.D. In the case of cabling standards outside of the USA, the standards are defined by ISO/IEC.
  • From time to time, ANSI/TIA and IEEE (responsible for the IEEE 802 network standards) talk and agree upon what actual physical Category cable standard should be used for a specific data rate, which is called “Application Bandwidth”

Application Bandwidth Defined

  • 10GBASE-T, 1000BASE-T, 100BASE-TX: They translate to, 10 Gigabit speed, 1 Gigabit speed, and 100 Megabit speed. FYI: 1,000 Megabits equals 1 Gigabit and 10,000 Megabits equals 10 Gigabits.
  • Application protocols are strictly defined, and literally define how fast your network is capable of running, this is application bandwidth.
  • These application protocols truly define what speeds you will see “on the ground”
  • For your network to function at the full bandwidth you seek, all components in the chain must support the same or higher application protocol...including your Ethernet cable. Sometimes, even the software you use can hold you back. Betcha didn’t know that! For a deep dive on how that can go wrong, check out our Free Whitepaper: Testing 10 Gigabit Ethernet Over Copper on a Shoestring Budget.
  • There is a direct correlation between application bandwidth and how much money you need to spend to achieve it. 10GBASE-T equipment is pricey, whereas 1 Gigabit equipment is more of a commodity and priced as such.

 

Information about Ethernet cable selection as it applies to application bandwidth can be found in our blog, What does 10/100/1000 Base-T mean?. For a more advanced discussion about what this translates to in real life, see The Need for Speed.

 

Putting It All Together

Up until now we have defined what these terms mean, but taken on their own they don’t tell you the story of how MHz may or may not matter in terms of Ethernet cable.

  • To support higher application protocols like 10 Gigabit (10GBASE-T), the Ethernet cable in question must support higher operating frequencies (Megahertz)
  • The higher the MHz, the more bandwidth the cable can support over distance
  • The physical construction of Ethernet cable plays a crucial role in this…
    • Thinner copper conductors, like what is found in Cat5e cable (24AWG), can only operate up to a certain Megahertz at a certain distance.
    • Thicker copper conductors, like what is found in Cat6 cable (23AWG) can operate at a higher Megahertz frequency over the same distance
    • ...therefore thicker copper conductors, all other things being equal, dramatically outperform thinner ones because they can support higher amounts of electricity which is exactly what Megahertz relates to. Thicker copper can accommodate more electrons.
    • Conductors are not the only criteria for supporting higher Megahertz. The following are also factors:
      • The thickness of the outer cable jacket
      • The thickness of the plastic insulation around the copper conductors
      • The number of twists per inch found inside an Ethernet cable on anyone wire pair. Read our blog, Why Are Wires Twisted Inside an Ethernet Cable? for more information.

 

So, the physical construction is all-important, and that is why ANSI/TIA has defined the Categories found in ANSI/TIA 568 2.D. What are the lowest frequencies needed to achieve a certain bandwidth at a certain distance?

Lowest Frequency to achieve bandwidth


The astute among you will notice that ANSI/TIA lists the maximum distance for the supported application bandwidth protocol. What many people don’t know is that many Categories of cable can support far higher application bandwidth at drastically lower footages. A great case in point, and defined by ANSI/TIA, is Cat6. Cat6 can support 10GBASE-T, as long as the length is kept to less than or equal to 165 feet (under ideal conditions mind you).

 

The takeaway?

You can, and I have tested it, run 10GBASE-T across Cat5e cable up to certain very short distances like 20 feet without any errors or issues.

That does not mean that Cat5e will Certify at any length to the Cat6A specification...it will fail dramatically in fact. This also does not mean you should exceed the ANSI/TIA specifications at any distance. You should not. The standards are there for several reasons--safety among them!

So, the more Megahertz supported means more bandwidth and therefore more possible speed.

Pictures are Worth a Thousand Words. 

What happens when you try and run 10GBASE-T across Cat5e at 200 feet?

What happens when you try and run 10GBASE-T across Cat5e at 200 feet?

 

Just kidding. The picture above does not really mean your cable will explode like a pipe. What will happen is, your network will start dropping packets and experience a lot of errors.

Think of the different Categories as pipes like this:

Pipe Categories

Each pipe has a different width, and that equates to the amount of data they can carry. This is why Cat6A can carry 10 Gigabit, and is actually specified to do so without errors.

 

The Big Question Finally Answered: Does More MHz Matter?

Absolutely, given you obey the rules. The MHz frequency is defined by the standard to allow for Ethernet cable installation with assurance that a certain bandwidth speed is achievable at a certain distance.

What Happens If You Have 550 MHz Cat6 Cable?

As previously stated, there are quite a few factors that go into whether a certain Category cable will reliably pass data at a certain distance--even if the MHz is higher than the minimum defined by the standard. Cat6 rated for 550 MHz is a “nice to have”.

It does not mean:

  • Cat6 can be driven to achieve what can be done with Cat6A
  • Cat5e will ANSI/TIA Certify as Cat6, even if the Cat5e cable is rated and tested to 250 MHz

 It does mean:

  • The Ethernet cable is produced to a high level of quality.
  • The cable is capable of a little more, under ideal conditions, than similar Category cable with a lower MHz rating. What, where, and how is up to you to experiment with.
  • The Ethernet cable is more tolerant of cross talk and the resultant transmission errors, within reason.

 

There you have it. Many folks over time have attempted to explain what this all means to the average DIY person, and with varying degrees of success. Hopefully you have a far better understanding now.

HAPPY NETWORKING! 

 

trueCABLE presents the information on our website, including the “Cable Academy” blog and live chat support, as a service to our customers and other visitors to our website subject to our website terms and conditions. While the information on this website is about data networking and electrical issues, it is not professional advice and any reliance on such material is at your own risk.

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