Q: I had a question at a seminar that a prominent distributor and a prominent cabling-system vendor would not (could not) answer. I have a customer with an embedded base of Category 5e cabling verified to 400 MHz. If I installed matched Category 6 components all the way through the channel, with the exception of the cable, could I achieve Category 6 data transmission rates?
Randy Hayes
Via e-mail
A: First, a word of caution. If your client requires a TIA-compliant Category 6 cabling system, then all of the components of the cabling system must be Category 6. Now that we have that disclaimer out of the way, the electrons traveling down the copper conductors cannot see the label on the outside of the cable jacket. So, if your client is only seeking Category 6 performance, then as long as the cable meets all the transmission and physical requirements of Category 6, electrically, it is Category 6 cable.
If you have a Category 5e cabling system in place using "400-MHz Category 5e" cable and you change to Category 6 connectors, and test with a Level III tester, you will, in all likelihood, pass Cat 6. But you may or may not have the same permanent link and channel performance that the TIA intended.
You see, the difference in your "super 5e" cable and Category 6 could be anywhere from significant to non-existent, depending on whether the "400-MHz Category 5e" cable will also meet the electrical balance requirements for Category 6—which, by the way, are still under development in TR-42.7. I know this is not exactly helpful, but not all the Category 6 parameters have been published, and none of the field testers test balance.
Electrical balance in the Category 6 standard is called longitudinal conversion loss (LCL), which is the difference between the differential and common mode voltage. The differential voltage across the circuit pair is the desired signal, whereas the common voltage is an unwanted signal that may have been coupled into the transmission line. If the line is perfectly balanced, the common mode voltage cancels out.
Remember why there was a Category 5e in the first place? There were a few parameters that IEEE needed for 1000Base-T that Category 5 had not been required to meet. Manufacturers did not want to guarantee that the cabling they already sold you would meet new requirements, and Category 5e was created.
Some Category 5 passed the new Category 5e requirements and some did not. To help users and installers determine what to do, TIA wrote a mitigation procedure—sort of, "change this and test, and if that does not pass, change that and test," with the last resort being to change the cable.
But this will not be the case between Category 5e and Category 6. TR-42.7 recently polled members asking if their companies would support further characterization of Category 5e, and as expected, the overwhelming answer was "no." Why? Because they now have a new Category 6 cabling system to sell you.
Bottom line—if you need 100% assurance of Category 6 performance, you will have to install Category 6 components, end to end.
Cat 6 in the standards
Are you confused about where to find Category 6 requirements in the ANSI/TIA/EIA standards? There are four specific places you must look:
- ANSI/TIA/EIA-568B.1, Commercial Building Telecommunications Cabling Standard Part 1: General Requirements, 2001 specifies a generic telecommunications cabling system for commercial buildings. This is the base document for most structured cabling system designs.
- ANSI/TIA/EIA-568B.1-4, Commercial Building Telecommunications Cabling Standard Part 1: General Requirements, Addendum 4, Additional Media for Commercial Building Cabling, 2003 recognizes balanced twisted-pair Category 6 cabling as a cable choice.
- ANSI/TIA/EIA-568B.2-1 Commercial Building Telecommunications Cabling Standards Part 2: Balanced Twisted-Pair Cabling Components, Addendum 1, Transmission Performance Specifications for 4-Pair 100-Ohm Category 6 Cabling, 2002 specifies insertion loss, near-end crosstalk (NEXT) loss, equal level far-end crosstalk (ELFEXT), return loss, propagation, delay and delay skew for 100-ohm 4-pair Category 6 cabling, cables and connecting hardware. This document is typically used by cabling manufacturers.
- ANSI/TIA/EIA-568B.2-6, Commercial Building Telecommunications Cabling Standard Part 2: Balanced Twisted-Pair Cabling Components, Addendum 6 (under development) will include a refinement of Annex H and Table E-3, both of which will change current connecting hardware measurement procedures.
Donna Ballast is BICSI's standards representative, and a BICSI registered communications distribution designer (RCDD). Send your questions to Donna via e-mail: [email protected].