Here at the wired blog we talk endlessly about our adapters and Ethernet silicon.  But there is more to a network than just an end node.  There is more to it than the link partner.  There is the cable that makes it all work together.  Without the cable you have just nothing (we don’t do wireless here on the wired blog) and without a network you have a static end point.  A network is dynamic, and the cable brings that rich content to you.

 

I was lucky enough to spend some time with the guys at Panduit*, a worldwide leader in cable manufacturing, at their HQ near Chicago, Illinois.  They have been doing electrical interconnects for ages.  They got started with power lines and power interconnects; it makes sense that they would eventually head into Ethernet cables.  I learned a ton from them about the specifics of the language around the cable, like the RJ45 connector is actually the female part that the cable plugs into, and the jack is what most people would call the RJ45, the end of the cable.  It reminds me of how specific language is developed around an industry.  I was at Panduit to shoot a video (it’s still under construction), but once it’s done, hopefully you’ll learn about 10 Gigabit BASE-T like I did during my visit.  I considered myself an expert, but they taught me a thing or two about the interconnect, the cable.

I asked Tom K from Panduit a few questions about Ethernet cables and here is how it went:

 

Q1:  What is the most common cable problem?

Believe it or not, Panduit has found the most common problem to be cable management.  As mundane as that sounds, poor cable management can quickly lead to wasted time making moves, adds, and changes as well as drops in network performance.

For example, a patch field or cross connect may start out nice and neat, everything is groomed and looks great.  Over time, with the pressure to get operational changes done quickly, cable management drops off the list of priorities.  People have the best of intentions, thinking “I’ll get back to it later,” and before you know it, the patch field has shifted from being neatly dressed and identified to a disorganized sprawl.

The ironic part is that, in the long term, one is not saving any time at all.  The messier the patch field gets, the more time it takes to make changes because one has to double and triple check to make sure they are making the right move.  It also makes airflow through the cabinet a problem. Finally, from an installation or permanent link standpoint, we often find that poorly managed cables coming out of the jack have too tight of a bend radius, which could cause the link to fail.

 

Q2:  How much of an impact on a network’s performance do the wrong cables have?

In the context of moving towards 10GBASE-T, a lot.  As an example, let’s say that for whatever reason, a 10GBASE-T link is deployed over CAT5e cabling, rather than CAT6A cabling, which is designed to handle 10 Gig traffic.  The net effect of this decision would be a higher bit error rate than the 10GBASE-T standard calls for, as CAT5e cannot support the cabling requirements for 10GBASE-T.  There also would be more internal crosstalk such a Near End Crosstalk (NEXT), Far End Crosstalk (FEXT), and Alien Crosstalk (AXT).  (NEXT is cross talk between the cable pairs that occurs near the 10GBASE-T PHY, FEXT is crosstalk that occurs at the far end of the link away from the PHY, and AXT is cross talk that occurs to signals coming from another cable laying next to the one in question.)  Overall, if the wrong cabling is used, the link will drop packets and overall network throughput and performance will be compromised.

 

Q3:  What are some tips on moving from CAT5e to CAT6a?

First tip would be to use proper installation techniques.  CAT5e and 1000BASE-T are a little more forgiving than 10GBASE-T given the higher frequencies used in 10GBASE-T, and the impact of noise is more troublesome too.  An example would be un-twisting too much of the copper pair when terminating CAT6a in a RJ-45 jack.  For 1000BASE-T or CAT5e, excessive un-twist may not impact the performance of the link.  However, with the tighter tolerances of 10GBASE-T and CAT6a cabling, the balance of the twisted pair might be impacted enough by too much un-twist to the point that crosstalk and external noise sources may impact the performance of the link, which then would adversely affect throughput and overall network performance.  This problem can be solved by using the proper tools from the connector manufacturer.

Second tip would be to stress the importance of link testing, or of using cables that are designed to reduce the time and types of testing required.  Testing the usual parameters, such as Near End Crosstalk (NEXT) and return loss, to name just two, are important. However, because of the frequencies involved and the modulation levels that are used for 10GBASE-T, people are most concerned with Alien Crosstalk (AXT). This effect can occur when twisted pair cables are laid down right next to each other in cable raceways, increasing the chance of signal coupling.  Testing for Alien Crosstalk can be a time consuming, and therefore, expensive process.  Fortunately, Panduit’s standard CAT6a and CAT6a-SD (small diameter) cables use a patent pending technology that suppresses Alien Crosstalk.  This means one does not need to perform testing for AXT with Panduit’s CAT6a solutions, which saves the time and expense of testing for it.

 

Here is a link to the Tom’s Hardware* article that  showed how we test for exactly the kind of stuff Tom is talking about  and more.

 

If you have questions for the Panduit guys, let me know in the comments.

Thanks for using Intel Ethernet.

(update:  There was an error in the link to Tom's Hardware)