 In this, the first of a series of articles on 10 Gigabit where we plan to expose some of the fact and reality behind the hype, we take a look at the two most fundamental questions – why bother with UTP at all and how good are those guarantees?
To screen or not to screen?
In the initial cabling objectives set by the IEEE to support 10 Gigabit, screened solutions in the form of Cat 7, or Cat 6 FTP with some additional requirements, were designated as being capable to support the full 100m distance. For the first time, due to real issues concerning externally generated ‘alien’ noise, UTP was recognised to have potential weaknesses which could limit transmission. So why are we so obsessed with UTP when on the face of it screened solutions have already been identified as offering a better choice?
To try to get to the truth let us look at some of the reasons why UTP has up until now, been considered the most suitable media for many installations.
UTP will be cheaper?
When comparing a standard Cat 6 UTP with a standard Cat 6 FTP this may be true. But this is not necessarily true when comparing a supposed 10G capable UTP system with a screened solution. The technology required to eliminate Alien xtalk by ‘geometry’ is likely to prove at least comparable with cost of screening. Couple this with the considerably larger dimensions which require far larger traywork, less cable capacity in wall trunking, and reduced cabinet densities in order to handle the fat patchcords and the perceived cost benefits of UTP are quickly eroded.
UTP is easier to install?
10G UTP is a completely different beast to standard Cat 6. It is generally bigger and less flexible even than individually screened Cat 7 STP PiMF cable. And that is before you consider the patchcords which in many cases have large solid conductors and minimum lengths of around 2m. The horizontal cables are generally too big to fit into familiar reelex style boxes and many of the designs are intended not to be round or are spectacularly ‘knobbly’ making them difficult to install. By comparison, terminating a drain-wire seems not such a difficult task after all.
UTP is easier to test?
There wasn’t a lot of difference in this until Alien cross talk raised it’s ugly head. Unfortunately it is currently impossible to test this in the field. In theory this applies to both UTP & FTP solutions but the reality is quite different. Lab testing has shown that screened systems pass the alien xtalk requirements with huge headroom, even under the worst conditions whereas the supposed 10G UTP solutions provide only marginal passes at best, even under easy controlled lab conditions. And that is without taking into account more stringent Alien Far End xtalk measurements. The conclusion to be drawn is that screened solutions can be installed with the relatively safe knowledge that they will comfortably pass the requirements but that UTP solutions, being close to the limit, need field validation to establish whether they are compliant or not.
UTP has existing installed base?
So what? We are not seeing 10G cabling being tacked onto existing systems for moves, adds, and changes (MACS). 10G is being installed in new build projects or refurbishments. So the historical cabling is irrelevant. UTP is of course a choice – but that choice should be made on whether it provides the right cost v benefit objective for the current and foreseen needs – not merely because it was right last time.
But what about all those guarantees of ‘compliance’…..
There is no doubt that manufacturers will honour their own guarantees – which is why they are very careful about what is actually written into the documentation!
So if you are considering a system on the basis that the risk is covered by the supplier, just be sure that the warranty offered clearly states that the system will support the finished ratified application standard. Despite the multitude of ‘Guaranteed 10G’ solutions on the market, most of these do not actually guarantee the final application will actually work!
Typically, guarantees take one of three approaches:
- Compliance to published draft standards
Sounds good – but does it mean your system will work? The cabling standards are at very early stages, particularly with respect to component standards. More importantly, for key parameters such as Alien FEXT, the full detail of the test methods have yet to be defined leaving manufacturers to choose their own method to achieve ‘compliance’. Results of Nexans testing which were recently presented to the IEEE have clearly demonstrated that different test methods will give very different results. But more importantly is that for Alien Crosstalk which is so marginal on UTP, you will have no way to tell if your installed system is ‘compliant’ or not.
- Guarantee a ‘Shannon Capacity’.
Guaranteeing your system has theoretical ‘capacity’ to transmit 10 or even 18 Gigabits is not the same as saying it is guaranteed to support the specific application of 10GbaseT.
- Add a get out clause in the small print.
Examples may include disclaimers to future changes in standards, or actually guaranteeing to published ratified standards only, with an application warranty along the lines of, ‘we guarantee any application provided the standards say it should work on standard Cat 6‘!! So if the IEEE say 10GbaseT will work on standard Cat 6 UTP but with a maximum length of 40m, then that is what is guaranteed.
Sour grapes?
One could be forgiven for coming to the conclusion that Nexans appears to be taking an anti-UTP stance when it comes to 10 Gigabit. The cynics may even surmise that this is sour grapes as we don’t have a UTP solution on the market. However again this would be a misconception. The majority of Nexans LAN cabling business is UTP and we have significant interests in UTP manufacturing. It is true that in Europe we have yet to launch a UTP 10G solution but in the USA, Nexans has both screened and unscreened products on the market and our position there is clear – the best solution is screened whilst we also offer the ‘best UTP solution’ available. Clearly market demands will necessitate a UTP launch in Europe too, but this does not mean that our position and recommendations will change - Nexans position has always been to offer unbiased choice based on what is right for a particular customer. Until the field testing issues for validating critical alien crosstalk parameters are resolved then our belief is that screened solutions offer the optimum cost v benefit solution for 10 Gigabit copper applications.
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