CAT 6 FAQ's

Straight Talk on Meeting Proposed Standards
BY JANE LIVINGSTON AND JAY LAHMAN

WHAT ARE THE MOST IMPORTANT FACTORS TO CONSIDER IN BUYING CATEGORY 6?
To meet the proposed standards, a Category 6 system must achieve specific performance criteria for NEXT, FEXT, attenuation and return loss. These measures must be achieved so the Category 6 products exhibit link, channel, and most importantly, component compliance with the proposed standards.

WHAT IS COMPONENT COMPLIANCE?
Component compliance means that each Category 6 product, including patch panels, patch cords, cable and modular jacks can test and perform as individual components as outlined in the proposed Category 6 standards. Component compliance means that each product has headroom of its own. In fact, component compliance is the only way to ensure that a Category 6 network will actually deliver Category 6 performance.

To understand the importance of component compliance, it is helpful to first understand link and channel compliance. In testing a link, electrical performance is measured from the modular jack at the work area, through the horizontal cable to the first patch panel or connecting block of the cross-connect. Link testing does not test the station cord, the equipment cord, or even the additional patch cords, patch panels or connecting blocks in the cross-connect. Testing for channel compliance goes one step beyond link testing by including station cords and equipment cords. Link and channel tests only measure how cabling infrastructure products work together, not the performance of individual components.

Link and channel compliance are therefore incomplete indicators of a Category 6 system. What these tests don't show is how one under-performing product must take advantage of available headroom of another product in the channel. Channel tests do not show, for example, how the generous headroom typically available in horizontal cable makes up for the poor performance of a plug. With Category 6 products that are only link and channel compliant, you cross your fingers and hope one product compensates for the other. And without component compliance, there is no way that Category 6 products can meet an important part of the proposed standard - backwards compatibility.

WHAT IS BACKWARDS COMPATIBILITY?
Think of backwards compatibility as open architecture. Backwards compatibility, which can only be achieved with component compliance, is a requirement of the proposed Category 6 standards. TIA specifically states "next generation cabling, components and mated connections shall satisfy all requirements of their category in addition to all existing lower category specifications."

What this means is that mating a Category 6 patch panel with a Category 5e patch cord will result in Category 5e performance. And this means that mating a Category 6 patch panel with a Category 3 patch cord will result in Category 3 performance.

Backwards compatibility also implies vendor independence. So, mating a Category 6 patch panel from vendor A with a Category 6 patch cord from vendor B will result in performance that meets Category 6 transmission requirements. Again, this is only possible with a component compliant system.

Backwards compatibility is not a new concept in the world of twisted pair transmission requirements. This is required for Category 5e and Category 5 products, too. In fact, TIA states that Category 7 products must be backwards compatible with products rated for Category 3, Category 5, Category 5e and proposed Category 6.

To measure jack performance, the proposed standards have set minimum performance levels when jacks are mated with plugs. To achieve a mated jack and plug NEXT of 54 dB at 100 MHz in the 3,6 - 4,5 pair combination, the proposed Category 6 standard requires that the plug exhibit a de-embedded NEXT range of 36.4 to 37.6 dB.

The 100 MHz frequency is useful here as a reference point for backwards compatibility with Category 5e. To ensure backwards compatibility with Category 5e components, this same mated jack/plug connection must test at 43 dB at 100 MHz with a de-embedded NEXT range of 34.4 to 37.6.

As detailed in the standards, the Category 6 jack must perform in two, overlapping de-embedded plug NEXT ranges - the 36.4 to 37.6 dB range for Category 6 and the broader 34.4 to 37.6 dB range for Category 5e. This takes more work because engineers must tune a jack to a broad range of plug values, not just for the more narrow Category 6-only values.

From an engineering standpoint, it is much easier to create a jack that delivers Category 6 performance without backwards compatibility. In general, the higher the de-embedded plug NEXT magnitude, the easier it is to tune for Category 6 performance. So by tuning to a higher de-embedded NEXT range, way above the 36.4 to 37.6 dB range and up closer to 54 dB, manufacturers can indeed deliver a Category 6 jack that will pass in link and channel testing. It is also easier to tune a jack to a narrower range of de-embedded plug NEXT values that only address Category 6, which ignores clear requirements in the proposed standards that jacks must be tuned for broader dB ranges for backwards compatibility.

The result of this shortcut engineering is a Category 6 jack that will fall short of 43 dB at 100 MHz in the 34.4 to 37.6 dB range for Category 5e. And what happens when the Category 6 jack falls short of 43 dB at 100 MHz? It means that for Category 6 products that are not backwards compatible, mating a Category 6 patch panel with a Category 5e patch cord will result in channel performance below Category 5e.

[top of page]     [next page]