December, 2012 Issue of Cabling Installation & Maintenance Magazine
The TR-42.7 Subcommittee, establishing specs for 40-Gbit/sec twisted-pair infrastructure, has chosen Cat 8 as the next generation cabling standard.
BY PATRICK MCLAUGHLIN
It looks like the nomenclature that will be used for the next-generation twisted-pair cabling solution, as specified by the Telecommunications Industry Association (TIA; www.tiaonline.org), will be Category 8. The TIA did not develop a set of Category 7 or 7A specifications, as the cabling-standards-development organization International Organization for Standardization (ISO; www.iso.ch) did along with the International Electrotechnical Commission (IEC; www.iec.ch), and at this point the TIA likely never will. Based on the goings-on at an October meeting of the TIA's Engineering Committee TR-42 Telecommunications Cabling Systems, the term Category 8 was accepted as the next-generation nomenclature.
The TIA publishes meeting reports of its engineering committees and subcommittees. The information in this article comes from meeting reports of TR-42 and the Subcommittee TR-42.7 Telecommunications Copper Cabling Systems, as well as primarily from a presentation made during an online seminar hosted by Cabling Installation & Maintenance and held in late October. In that seminar, Nexans' (www.berktek.com) technical manager for standardization and technology Paul Vanderlaan delivered a presentation updating the progress of TR-42.7 on this initiative, as well as efforts being made within ISO/IEC and the Institute of Electrical and Electronics Engineers (IEEE; www.ieee.org). The ISO/IEC efforts, like the TIA's, are aimed at establishing specifications for twisted-pair cabling systems to support data transmission rates of 40 Gbits/sec. The IEEE efforts focus on the development of a next-generation "Base-T" application. Vanderlaan emphasized in his presentation that the work of all three of these groups is in its preliminary stages.
The online seminar will be available for viewing on-demand through late April. But importantly, the aforementioned standards bodies continue to meet regularly to advance their efforts, and it is likely that significant progress will be made on all fronts in the span of time in which the seminar can be accessed.
In the introductory portion of his presentation, Vanderlaan answered the question that may be on the minds of many: Why are these groups working on a next-generation Base-T application and the cabling infrastructure to support it? "We believe there are several advantages and a distinct need to provide a twisted-pair solution, even when there already exists a twinaxial solution," for 40-Gbit/sec transmission, he said. Specifically, he noted, those involved in the efforts believe the establishment of a Base-T system will extend the reach of copper-based 40-Gbit/sec transmission beyond the 7-meter distance capability of the twinaxial-based 40GBase-CX4. This extended distance "will help enable end-of-row configurations in data centers," Vanderlaan said, adding that support of these end-of-row architectures is particularly important as data centers experience what he termed a "bandwidth explosion."
Additionally, a Base-T system will occupy a smaller form factor than the existing CX-4, essentially allowing more information to pass through the same physical space than can be accommodated via 40GBase-CX4 today. "We need to be efficient about how we push data through racks," he said. "Although a bandwidth explosion is taking place in data centers, an increase in square-footage availability is not. Higher data density is important."
Vanderlaan said that another advantage of establishing a 40GBase-T application and supporting cabling infrastructure is that "it eliminates vendor-specific compatibility issues. If you have a Vendor A switch, a Vendor B cable and a Vendor C switch on the other end of that cable, when they are connected in a Base-T-type system, they talk. There is no requirement to enter in a passcode, or unlock a feature to use non-vendor-specific cordage-as you might have to do with twinaxial. That's the way it has been in the past and that is the way we are striving to move forward in the future."
The IEEE initiative has passed the call-for-interest stage, with 52 engineers expressing a willingness to work on a 40GBase-T standard. As with other IEEE projects, this effort must meet the five criteria of broad market potential, technical feasibility, economic feasibility, compatibility and uniqueness. The study group that was assembled after the successful call for interest is actively working to satisfy those criteria.
Their focus is on the data center environment. Vanderlaan noted, "We don't envision a 40GBase-T need within the enterprise in the near future, so the obvious placement of this application is in the data center." He further explained that with a focus on the data center environment-known in general to have shorter link-length requirements than an enterprise environment such as a commercial office building-the group will explore different possibilities for balancing these three dynamics: the need to reach a certain distance, the need to keep power consumption in check, and the practical ability to manufacture product.
Lessons learned from the development of 10GBase-T include the importance of a reasonable level of power consumption and associated heat generation, as well as how those characteristics affect the ability to package equipment in a certain footprint or form factor. The idea that an initial 40GBase-T solution will specify a reach of less than 100 meters (and perhaps significantly less, to the tune of between 20 and 50 meters) is likely to better facilitate those other dynamics-power consumption/heat generation and the practicality of product manufacture.
While the IEEE works on those goals and objectives with a potential publish date of late 2014 that may well go to 2015, the TIA's TR-42.7 Subcommittee concurrently sorts out the twisted-pair cabling performance characteristics that will be needed to support 40GBase-T. The official name of the document that is in the initial stages of development is ANSI/TIA-568-C.2-1 Balanced Twisted-Pair Telecommunications Cabling and Components Standard, Addendum 1: Specifications for 100?? Next Generation Cabling.
That's where Category 8 comes in. During the online seminar, Vanderlaan stated that in a meeting held in early October, the group settled on Category 8 as the name for this next generation of twisted-pair cabling. The Category 8 specification will characterize electrical performance characteristics to 2 GHz. "All electrical parameters have TBD [to be determined] values," he explained. "Return loss, internal crosstalk, internal power-sum crosstalk and balance" are all characteristics whose performance levels are being discussed within the subcommittee, he added. In addition to what the values for electrical-performance characteristics will be, the manner by which those performance values will be measured at such extended frequencies also is under discussion.
Another point of emphasis that Vanderlaan made was that the alien-crosstalk performance levels initially being proposed-more stringent than those of Category 6A-suggest that Category 8 will be a shielded solution, but unshielded twisted pair has not specifically been precluded. Additionally, initial indications are that the RJ45-style 8-pin modular connector type will remain the standard interface when Category 8 is fully developed.
Vanderlaan also raised an issue with respect to Category 8 and backward compatibility. As previously mentioned, the TIA did not develop a Category 7 standard and is in essence "skipping" 7 as it progresses from Category 6A to Category 8. The ISO/IEC, however, did establish both Category 7 and Category 7A (Class F and Class FA) specifications. And the way it looks, the TIA's Category 8 will not be backward-compatible with the ISO/IEC's Category 7. Vanderlaan explained that standards-development groups have always strived to ensure that if an earlier-generation (e.g. Category 6) component is plugged into a later-generation (e.g. Category 6A) system, the system will achieve at least the performance level of the earlier generation (Category 6 in this example). We should not count on that when it comes to the TIA's Category 8 and the ISO/IEC's Category 7, he noted.
"Category 8 in its current form breaks the tradition of backward compatibility," he said. "The internal crosstalk requirements of Category 8 do not satisfy a Category 7 channel." The practical implication of that fact is that if a Category 7 component is used in a future Category 8 system, the system will not be guaranteed to achieve Category 7 performance.
The issue is particularly peculiar because Category 7 is an ISO/IEC spec, not a TIA spec. So some may position the argument that Category 8, a TIA specification, will be backward compatible with all previous TIA Category specifications. This backward-compatibility situation is "a current issue we need to address," Vanderlaan said. Another possibility is for the TIA to "redefine what backward compatibility means."
Again, as Vanderlaan emphasized, these developments are in their early stages and much will be determined in the months ahead. He did say this: "Category 8 will certainly work with all previous applications. It will work with 10GBase-T. It will work with 1G. And if you mix and match components, they will work."
The presentation covered a significant amount of information, including what has been presented here in this article as well as some detail on the ISO/IEC next-generation efforts, the possibility of a direct-attach Category 8 cabling specification coming from TIA, and observations about the five criteria the IEEE working group is addressing.
As previously stated, the progress of these standards-creation efforts is expected to advance steadily. An interim meeting of the TIA TR-42.7 Subcommittee was scheduled to take place in early December. The TIA, ISO and IEEE continue to work toward the establishment of specifications to enable 40GBase-T transmission in data center environments. ::
PATRICK MCLAUGHLIN is chief editor of Cabling Installation & Maintenance.