Cat. 6 products pass stability test
RJ45, the eye of the needle: the tighter, the better Cat. 6 products from R&M, “de-embedded” tested and certified / full compatibility and full performance in Class E
Cables and components of Category 6 are meant to enable Class E cabling systems, with a specified transmission frequency range going up to 250 MHz. As long as installers and users stay true to one manufacturer, this does work. But if a third-party supplier is involved, there could be trouble. The RJ45 connection is usually the eye of the needle, where bandwidth and performance get bogged down. With this in mind, Reichle & De-Massari (R&M), the leading Swiss manufacturer of cabling systems, arranged for their RJ45 connection
modules to undergo de-embedded testing and certification by an independent, accredited laboratory. The result is unrestrictedly compatible components and guaranteed transmission parameters for the network. If you take out your notebook PC and plug the standard patch cable into the standard socket, you will expect the LAN connection to work. If it doesn't, it isn't usually the fault of the twisted copper wires that were originally invented for telephone traffic and that now – four pairs in one cable – form the skeleton of the cabling system, at least on each floor. The eye of the needle is the plug connector.

In trunk connections, it was the last mile that limited the subscriber's bandwidth. On a LAN, it's the last few millimetres in the connection modules and plugs. This is where signals mutually affect each other and reflections originate, distorting the transmitted signal to the point of indecipherability for the receiver. Near-end crosstalk (NEXT), far-end crosstalk (FEXT) and return loss (RL) are therefore key parameters.

These effects can be partially compensated for by electrical means, and this has already been done for category 5 and 5e (enhanced) components. The lower bandwidth (up to 100 MHz actually used, but tested up to 125 MHz) made it possible to set quite generous tolerance limits: so generous, in fact, that interoperability between components from different manufacturers was a question of luck.
The tighter, the better
Manufacturers, installers and users eagerly anticipated the publication of the more stringent Cat. 6 limit values. They were published in America in June 2002 as TIA/EIA 568-B.2-1. Since then, this norm has been listed online by TIA as at the head of the “top selling standards”, and Frost & Sullivan, an American market research institute, expects it to give a boost to the industry. The second edition of the corresponding European norm for application-independent communications cable systems was ratified by CENELEC in November 2002 as EN 50173-1. The second edition of the related ISO / IEC 11801 standard was published in September 2002.

This puts a limit on the problem, but doesn't eliminate it. The reason is that crosstalk is measured via the commercial RJ45-plug, which at 250 MHz hits the limits of its physical performance. And this is where the question arises: are we actually measuring the test specimen – a connection module, for example – or are we measuring the entire test setup? Because of this doubt, some countries are still reluctant to accept the IEC version of the TIA norm.

This goes to the heart of the problem, the measurement method. Up to now, “mated” plugs and connection modules have usually been measured, i.e. it is the properties of the connection as a whole that are certified. And of course each manufacturer can select ideally matched pairs of plugs and sockets from his production line, and send them for testing. Consequently, the test result shows only a small excerpt from reality. It doesn't prove that all of the manufacturer's products invariably guarantee Cat. 6 performance right up to their performance limits.
This increases the risks for installers and users of network operations. If they stay faithful to one manufacturer, things mostly go well. If they go to a third party, things may go wrong. Worse still: if the user inserts a “bad” (but still compliant) Cat. 5 plug into a Cat. 6 socket, overcompensation may mean that the combination no longer meets Cat. 5 specifications.
De-embedded measurements, independently certified
R&M already put their products through a one-hundred-per-cent check. This makes them unique worldwide. And, in addition, R&M use a manufacturing process that guarantees the highest transmission quality between terminal block and socket.

Now, R&M are sending their Cat. 6 connection modules for de-embedded measurement and certification. This implies that the plug and the connection module are measured separately, i.e. “de-embedded”. Thus, for the crosstalk of a connection module to be certified, suitably checked testing plugs are required.
“For this purpose, we don't simply use plugs with average crosstalk values. We actually use plugs with values at the limit. This corresponds to the norm, and is appropriate to the situation in practice”, says Rene Trosch, head of development and the testing laboratory at R&M. “This is the only way to ensure that our Cat. 6 solutions are unrestrictedly interoperable, cross-compatible and backwards compatible. And we have it tested and certified by a neutral, independent body.”

R&M has entrusted the Danish laboratory DELTA with the task of certification. Among other things, DELTA are accredited for the type approval of components and systems used in application-independent cabling. “We have long been testing mated Cat. 6 connections”, says Erik Bech, Testing Manager at DELTA. “The manufacturer supplies plug and socket, and the test verifies the transmission characteristics of the pair. We are now also running genuine de-embedded tests, using testing plugs whose crosstalk corresponds exactly with the limits of the norm.”
Twelve cases have to be covered in the measurement of near-end crosstalk alone, so in the extreme case twelve plugs with the corresponding properties have to be found. That can't be done overnight. “We had to refine our testing methods over and over again”, reports Bech. “The procedure has now been finalized. We know the crosstalk in the plugs over the whole frequency range up to 250 MHz, with enough accuracy to achieve precise and reproducible results.” These results are fed back into product development at R&M.

Back in 2001, R&M became the first company in the world to obtain Cat. 6-certification from CENELEC (in accordance with EN-Norm) for their connection modules, on the basis of tests made by an independent laboratory. But this was still a “mated” measurement. R&M will be presenting the new de-embedded result for the first time at CeBIT 2003 in Hanover.
Why Category 6? Why Class E?
The two terms are usually equated. The difference is that the category specifies the components, whereas the class specifies the network. A Class E network has specific transmission data up to 250 MHz, and this is achieved reliably with components of Category 6. But where's the need for 250 MHz, when even Gigabit Ethernet manages with a bandwidth of approximately 80 MHz?

The answer is that transmission rate is not the only factor. In present-day applications, reliability counts. The permissible bit error rate under the Ethernet standard (10 EXP -8, i.e. one error in 100 million bits) has long been outdated and can interfere with time-critical applications such as production control or audio, video and VoIP transmission. What is being sought is an error rate of 10 EXP -12, i.e. a further reduction by a factor of ten thousand.

In the near future even 10-Gigabit Ethernet will be pushed through copper conductors, and this is also meant to operate with Cat. 5e components. But the transmission process is even more sensitive. The installation may simply not be good enough. In parallel with this, consideration is being given to using the four pairs of conductors in the cable in simplex, i.e. with two pairs for each direction rather than all four being used out and back. This would relax the requirements regarding reflection and crosstalk, but the lines could not be used with the present-day Gigabit Ethernet at the same time. A proposal is being worked on in the ANSI/TIA/EIA-854 committee.

Cat. 6 certification makes planning more reliable

We should not spend much time wondering whether we really need these high transmission rates. So far, Moore's law, which says that the transistor density in integrated circuits doubles every two years, has also been true of network bandwidth requirements.

How soon will we suddenly find we want to link not only a PC into the network but a remote file-server or a new application server? In that sort of case, an installation with de-embedded certified Cat. 6 components will give planning a high degree of reliability. All of this is also supposed to operate over Cat. 5e, as mentioned earlier. With a certified and entirely Cat. 6 solution, you're on the safe side.
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