Thanks for the information. However is their use mandatory for certification ? I think that your remark ( my emphasis) suggests not "
I have had a quick look at how a few audiophile ethernet cables have been specified by their manufacturers. Some claim Cat.x. Some use weasel wording to imply that they meet Cat.x. Others are honest enough to say that their “streaming” cables cannot be called " ethernet" cbles at all but then go on to list why (materials) their cables are superior 
. What fun!
A switch? I was fairly cynical but was given an English Electric (Chord cables) for trial, I placed this between my router and my Bartok.
The trial lasted less than 20 minutes and I bought it.
The increase in quality was small but noticeable.
I remain impressed, having a/b’s several times since.
It’s not a great financial leap and the return is just.
Certainly, give one a go.
Well, there’s specs compliance, and then there’s certification. The two aren’t quite the same; an Ethernet cable can be CATx specifications compliant but not necessarily certified.
Most Ethernet cable retailers buy spec compliant Ethernet cables in raw spools or custom moulded/terminated form from wholesalers like Belden. The raw cables are repackaged and terminated with appropriate RJ45 heads and the finished cables are compliance certified (or not, depending on their target end customer market).
Some cable wholesalers do also sell retail, like Nexans for example, with their LANmark branded patch cords which are certified at factory. While retailers like Telegärtner certify their Ethernet cables with 3rd party labs GHMT and UL
Cables from those folk above are generally much better than most “Audiophile” Ethernet cables which I’m guessing aren’t certified, just specs compliant cables from wholesalers, repackage and terminate with speciality RJ45 connectors and marked-up 1000% 
Mind you, some audiophile Ethernet cables do measure really well, like Audioquest’s RJ/E Diamond, so, should in reality have no problems being certified (but aren’t, probably because of the extra cost involved).
You guys heard it direct from dCS above, it’s just data bits, but for me I went with a decent $250 CAT8 cable just because it frankly looked nicer than a cheap telephone line looking Cat5… it was purely for the aesthetic… but truthfully 90% of the reason I have nice power cables and interconnects is also aesthetically it looks nicer than cheap plastic cables…
If there is a .01% improvement to sound, well that’s just gravy.
You might have had a 0.01% improvement… which is effectively zero. But others do get audible improvements; and it’s not always from expensive kit.
The Supra Ethernet cable is cheap, but better than the BJC. Don’t know why and don’t really need t know. I could hear it. Tried it twice now, many months apart, same result. Minor but audiable .
dCS don’t test every possible home setup, they only have so much testing thy can do. So some ppl may get bigger improvements at home.
You have got to listen for yourself and decide… the advice can only ever be a starting point.
Thanks Jon 
oh don’t hold me to that .01% … I just threw that out there so as to reinforce my point that the aesthetic of a nice cable is enough for me to spend the money … albeit I’m not buying the cream of the crop $70,000 speaker cables, and $30,000 AC power cables either… 
Just to clarify David that although i run Supra ethernets into and out of my network switch, it was the one from the switch into the Bartok that made the audible difference.
Sam, I hear you 
and i think most of us are guilty of want vs. need at some point… Alot of want involved in some of my hifi purchases 
I just wanted to do justice to the Bartók, so floated the idea of changing/updating my network.
Naim and Linn have the same take on Ethernet cables, as dCS does, which seals the deal for me.
Personally, I wouldn’t buy a £4.99 one from Tesco (Sorry you Tesco shoppers!), but neither would I buy an AudioQuest Diamond. 
There is definitely a difference in the way cables are manufactured, so bearing that in mind is important when choosing cables.
Which is pretty much exactly why I bought the BJC and then the Supra to try out and compare. Not from Tesco and not super expensive. Just well made and built to spec.
Hi Jon…So are are you using both BJC and Supra cables in your setup?
BJC appears to be well respected across various hifi communities.
Thank you James for this superbly clear response. I have copied your response and will use it anytime I hear more about “just because audiophile” network cable superiority from anyone.
I will add thought that the comment later on about buying cables that are aesthetically superior from “telephone line” stuff also has merit. Bottom line for me anyway - is that I would gladly pay for things I appreciate not for snake oil wrapped up in “quantum speak”.
You have helped me and others with your clarity.
I tried Supra. Enthusiastically. Went back to BJC. Not shielded and test results for each cable’s conformity with spec. Zero noise, which was not the case with the Supra [and may have been due to the shielding].
I now have an EtherREGEN in my network and just borrowed a Melco N100 to try out. Interestingly I have switched back to the BJC to plug into the A side of the EtherREGEN.
But have to test out various configs and see what sounds best; if anything.
Placebo really works and can do miracles.
Packet trasmission can’t be compared to not controlled SPDIF. No way is there a difference in sound as you sent packets and frames with error control. If packets are not missing, no problem and they are not lost in LAN
Well an awful lot of people don’t agree with you. The understanding of how computer systems and networks affects digital audio systems is far from complete.
Seems we are still very much on the learning curve.
People run many different setups and each one will not be affected in the same way by something being changed.
I wouldn’t be so quick to dismiss the views of so many others.
I’m not necessarily disagreeing with this sentiment in the abstract—there is always something new to learn—but this same notion is all too often used to obscure the engineering we do know that tells us that, absent packet loss and/or the injection of noise, there is simply no science behind a lot of the Ethernet snake oil. I am not one who subscribes to “bits is bits,” and writes it off at that, but I do believe a large variety of “audiophile” Ethernet cables and boxes are nothing but snake oil with zero engineering behind them. Audiophile paranoia is so easy to prey on.
It’s fine to say we don’t know everything, but that’s not an excuse for refusing to provide engineering explanations for what people claim to hear. We are now decades into digital audio. It’s not in its “infancy” any more. Do we really prefer to believe that companies like dCS, Merging, MSB, Meitner, CH Precision, etc., know less about the dynamics of digital audio than the host of companies with a motivation to sell audiophiles on audiovoodoo?