In the beginning, there was 10Base-T, and it was good. Then in the early 1990s, we were all “abuzz” about 100Base-T; and then in 1999, 1000Base-T (Gigabit Ethernet) was the application to support.
More recently, copper cabling has begun its 10-Gigabit Ethernet era. In November 2003, the Institute of Electrical and Electronics Engineers (IEEE; www.ieee.org) formed the IEEE 802.3an task force, whose mission was the technical development of a new physical layer (PHY) that defined operation of up to 10 gigabits per second (Gbits/sec) with full-duplex channels over four-pair cabling, with each pair supporting 2.5 Gbits/sec in both directions simultaneously.
In July 2004, Draft 1 of IEEE 802.3an was issued, providing the roadmap and objectives for the standard. The 10GBase-T objectives are:
• 10-12 bit error rate (BER);
• 10 Gbit/sec data transmission over at least 100 meters of Class F cabling (Category 7);
• 10 Gbit/sec data transmission over at least 55 meters to 100 meters of Class E cabling (Category 6).
Unlike the ISO and TIA standards processes, when the IEEE starts a project, they assign a date for release of the completed standard. IEEE 802.3an is set for July 2006. (For review of current task force materials, see www.ieee802.org/3/an/public/material)
What we know so far
Alien crosstalk is the problem. The IEEE 802.3an group identified reduction of alien crosstalk, near-end (ANEXT) and far-end (AFEXT), and Shannon throughput-capacity of at least 18 Gbits/sec as two of the most critical elements needed in cabling for 10GBase-T.
TIA TR-42 is developing TSB-155, “Additional Guidelines for Four-Pair 100 Ohm Category 6 Cabling for 10GBase-T Applications,” which will characterize what length of a Category 6 UTP channel will support 10GBase-T. The current working copy of TSB-155 says that Category 6 UTP cabling will support 10GBase-T up to at least 55 meters.
Our installations typically result in bundles of cables in horizontal raceways, such as cable tray and/or conduit between a telecommunications room and the work areas.
The principal challenge for Category 6 UTP cabling to support 10GBase-T is the “alien crosstalk”-the data interference induced by pairs in the adjacent disturber cables onto the pairs of a victim cable. Because this noise is not a signal generated by the victim, the transceiver cancellation circuitry cannot be trained to cancel it out from the data stream, which is possible with crosstalk induced by pairs within the victim cable.
So, based on channel performance, alien crosstalk will be the determining factor as to what distance can be supported-between 55 and 100 meters.
Longer distances are possible, but so far, there is no way to certify that any cabling channel will support 10GBase-T, regardless of length.
Is this helpful? I say, “No!” What if you add a cable or remove a bundle of abandoned cable and disturb the lay of the other cables in the pathway? Then you risk having a change in performance in the installed and legacy Category 6 UTP cabling.
TIA 568-B.2-10
TIA TR-42 is also developing TIA 568-B.2-10, “Commericial Building Telecommunications Cabling Standard, Part 2: Balanced Twisted-Pair Cabling Components, Addendum 10: Transmission Performance Specification for Four-Pair 100 Ohm Augmented Category 6 Cabling.”
The current working copy of TIA 568-B.2-10 characterizes a new Augmented Category 6 UTP cabling to support 10GBase-T to a full 100 meters. TIA 568-B.2-10 is “expected” to be released along with the IEEE 802.3an standard in 2006. Sooner would be better, since the availability of network equipment tends to predate the ink drying on the IEEE 802.3 standards as well.
Currently, Augmented Category 6 has several open issues. Channel requirements on most parameters, including the alien crosstalk, have been addressed and closed. But alien crosstalk testing is new and requires developing a test method not previously addressed in the standards. The most demanding configuration for testing alien crosstalk would be six disturbing cables wrapped around one victim cable.
After walking the show floor and viewing the vendors’ new cabling offerings at the BICSI conference in January, you’d find it hard to believe that there is not yet a standard for Augmented Category 6 cabling, or field testers to test it. But that is the case.
Cabling manufacturers are currently developing product solutions that meet the proposed alien crosstalk requirements of TIA 568-B.2-10 in order to achieve 10-Gigabit Ethernet over Augmented Category 6 UTP. But until the first draft of Addendum 10 is issued, one has to question what information is available to industry (outside of the members of TR-42.7) to confirm designs and validate manufacturers’ compliance claims. To my knowledge, none!
Better, faster, bigger
Augmented Category 6 UTP cables look and feel different than Cat 6 cables. In most cases, Augmented Category 6 cables have a larger diameter to help mitigate alien crosstalk. Space is used to increase the distance between the pairs in one cable from pairs in other, adjacent cables, and is intended to lower alien crosstalk noise between signaling pairs in adjacent cables.
Message to TR-42.7: Please remember that we mere mortals still have to place, terminate, and test the systems that you are creating. Fat, stiff cables that are difficult to place, a struggle to strip and terminate, and tricky to test (I have this horrible vision of a tester the size of a Cooper Mini being wheeled around the project site to field-test for ANEXT) are not “craft friendly.” If our installation time increases, so does the owner’s cost-not just for the new components that you are designing, but also for the additional labor necessary to deal with these issues. Time is money.
As the roadmap to 10-Gig continues, so too does the work on copper cabling to support it.
What about Category 5 and 5e?
Category 5/5e has a bandwidth of 100 MHz; Category 6 has a bandwidth of 200 MHz characterized to 250 MHz; 10GBase-T as specified by the IEEE 802.3an task force requires a bandwidth of 500 MHz. If 10GBase-T will work on Category 6, then couldn’t it also work on Category 5/5e? Some experts say yes, while others disagree.
Once all the TBDs (“to-be-determineds”) in TIA 568-B.2-10 are replaced with actual requirements and the experts reach agreement on those requirements, then the testing can begin as to what will support 10GBase-T and at what distance. But it is not looking good at this point.
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]