Terminology Tuesday: Delay Skew


I was asked to proof read a new piece of literature the other day, when someone looked over my shoulder and commented about the photo on the page. “Wow, someone has to punch down all those wires individually?” I started to explain the punch down process, and moved into a more technical explanation of how and why the cable pairs are twisted, and the difference in punching down Cat6 wires today, compared to the ease of punching Cat 3 years ago. When I got to NEXT and Delay Skew, I stopped talking, this was way too much information for the simple comment that was made off-the-cuff.

But I like the technical side of cables, datacom and security products. So I got this great idea to start a new blog column. Welcome to Terminology Tuesday. Each week I will pick a new industry term to discuss. They may be technical, or they may be “buzz words” like “M&Ms”. If you want to know what M&Ms refers to, you will have to come back and check out next week’s post, which will be “Contractor Buzz Words” (and yes, I just decided on that topic for next week as I was writing this).

What is Delay Skew?

As you probably know, Category cables are often referred to as “UTP” – which stands for Unshielded Twisted Pair. Each cable pair is twisted at a different interval, or twist ratio. Since the pairs are twisted, technically it takes the data signal longer to get from one end of the cable to the other. (Picture the cables untwisted and laid flat, the more twists they had, the longer they will be when untwisted). So, the closer the twist (shorter interval between twists), the longer it takes for the data to travel down the cable. With the varying twist ratios on the different pairs within the cable, the data will arrive at the receiving end at different times.

Now that I have explained the basics of the cable construction, I can easily explain the term “Delay Skew”. The time it takes for the data signal to travel down a single wire from source to destination is called the “Delay”. The “delay skew” is timing differences between the signals spread across the various pairs.

If you want to know more about delay skew, read this great white paper from Siemon.

Have a datacom or security word or concept you would like to see explained “in layman’s terms”? Let me know and I will add it to the list for Terminology Tuesday.

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