Inching closer to final standards for high-speed twisted-pair networking and cabling

The IEEE’s 25 and 40GBase-T specifications move along, potentially joined by 50G, while Category 8 is near the finish line.

By Patrick McLaughlin

Specifications from multiple standards bodies are nearing their respective finish lines, suggesting that 2016 will be the year in which 25GBase-T, 40GBase-T, and Category 8 cabling all become standardized. Each of the specifications has been in the works for multiple years, and if all goes well it may not be long before the specifications are completed.

25, 40, and 50?

In an article we published nearly a year ago (“IEEE to study new Base-T data rates for data centers and enterprise applications,” February 2015), IEEE 802.3bq Task Force chair David Chalupsky explained that the scope of 802.3bq could change to include specifications for 25-Gbit/sec transmission in addition to the document’s original 40-Gbit/sec specifications. Chalupsky explained, “As bandwidth needs exceed 10 Gbits/sec, 25/40GBase-T efforts will address enterprise server room and data center application requirements, using similar modulation techniques for the respective specifications. Largely based upon 10GBase-T signaling whose data rate has been sped up four times, the 40GBase-T project took a hard look at the 100-meter reach convention used for prior Base-T PHYs. With server-to-switch connections as the target use for 40GBase-T, 30-meter reach was seen as sufficient for installations using middle-of-row or end-of-row placement for switching equipment.”

Because the addition of a 25-Gbit/sec specification would be a modification to the original project, incorporating 25G specs required approval of a project authorization request (PAR) modification within the IEEE 802.3bq Task Force. That modification was approved in September 2015. Based on the timeline shared at 802.3bq’s November 2015 meeting, September 2016 is the target timeframe for standard finalization.

As Chalupsky noted in early 2015, the IEEE 802.3bq Task Force “has been collaborating with cabling standards organizations on defining Category 8 cabling specifications. Although first defined for 40GBase-T, Category 8 is also anticipated to be the target channel for 25GBase-T … Analysis to date of 25GBase-T on Category 8 has shown that it is generally an easier problem to solve than running 10 Gbits/sec on 100 meters of Category 6A. This means that the cost per bit, and power per bit, of 25GBase-T products could decline quickly to rather economic levels. Secondly, this is the first time that IEEE 802.3 has specified two new higher-speed Base-T PHYs that run on the same cabling system. This creates an inherently long life roadmap for a Category 8 cabling system: Use it for 1000Base-T or 10GBase-T today, and the same infrastructure can be reused in the future for 25GBase-T or 40GBase-T operation.”

Recently it came to light that it’s possible a third speed-50 Gbits/sec-may someday also target Category 8 cabling. When 25GBase-T was added to the 40GBase-T specification, the first official step in that process was a call for interest within the IEEE 802.3 Working Group (of which 802.3bq is a subset). That call for interest is a first step in the development of any specification that 802.3 produces. If the call for interest is approved 802.3 forms a study group, which meets before developing a PAR. The PAR takes a potentially winding path through the study group and the 802.3 Working Group before potentially being approved. That long-winded-but-abbreviated description of the very beginning of the standards process serves as a disclaimer, because the idea that a 50GBase-T specification may someday come to fruition is just that-an idea. There has not been a call for interest for 50GBase-T and, according to a member of the 802.3bq Task Force, the 25/40GBase-T specification will be completed without a 50GBase-T component. If 50GBase-T ever becomes a reality, it will do so after the finalization of 25/40GBase-T.

Nonetheless, in the current “idea” stage that precedes a call for interest, the intent would/will be for 50GBase-T to operate over Category 8 cabling. That possibility has at least a couple implications for the Category 8 standard. As Masood Shariff, engineering senior principal with CommScope, pointed out in an article we recently published (“Category 8 questions answered,” October 2015), “IEEE 802.3bq Task Force is collaborating with TIA TR-42.7 and ISO/IEC/JTC 1/SC 25/WG3 to ensure consistency and compatibility of the cabling specifications with the ‘link segment’ specifications in IEEE 802.3bq applications. Liaison letters to clarify requirements or provide additional information are generated at most meetings and latest drafts of the TIA and ISO Category 8 specifications are sent to the IEEE 802.3bq committee where they are posted in a ‘private,’ password-protected area for members to review and comment. The relationship between IEEE 802.3bq and its companion cabling standards organizations has been very positive and constructive, with several common members attending the meetings.”

Category 8, or wait?

Via regular correspondence, members of the TIA TR-42.7 Telecommunications Copper Cabling Systems Subcommittee are aware of the potential call for interest for 50GBase-T. As such, at the most recent meeting of the TR-42 Telecommunications Cabling Systems Committee meeting in October, TR-42 decided it would not immediately publish the Category 8 cabling standard even if TR-42.7’s work on the standard was complete.

The thinking is that if indeed the IEEE moves forward with 50GBase-T and targets Category 8 as the supporting media, the TIA will hold open the possibility that Category 8’s electrical performance requirements may need to be made more restrictive (i.e. better-performing) in order to support 50GBase-T.

On one hand, waiting to publish Category 8 for this reason would save TR-42/TR-42.7 from having to create a “Category 8A” standard (or something with similar nomenclature) to support 50GBase-T. On the other hand, consumer behavior patterns have shown time and again that official standardization of a Category cabling performance level prompts an increase in purchases of that technology. So for the few cabling vendors that have developed systems intended to comply with the forthcoming Category 8 specifications, the wait may continue for the market as a whole to gain a satisfactory comfort level to invest in Category 8 cabling.

TR-42.7 meets on a more-frequent basis than TR-42’s thrice-yearly schedule. Once TR-42.7 hammers out the final details of the ANSI/TIA-568-C.2-1 Specifications for 100Ω Category 8 Cabling specification, TR-42 may choose to have the standard published rather than to hold it up pending IEEE’s action or inaction on 50GBase-T.

Whenever ANSI/TIA-568-C.2-1 is complete, the Category 8 work will not be entirely over for TR-42.7. Valerie Maguire, director of standards and technology for Siemon, explained in our recent “Category 8 questions answered” article: “TIA is developing requirements for Category 8 cabling constructed from Category 8 components and is also undertaking an initiative to develop Class II cabling requirements that will harmonize with ISO/IEC. The Class I and Category 8 cabling specifications support modular RJ45-style connectors. The performance associated with Class II cabling can only be realized when Category 8.2 cables are used in conjunction with non-RJ45 interfaces such as the Siemon TERA connector.” In a Web-delivered seminar held November 5, Maguire said, “Substantial component-related work needs to be done” on the TIA’s Category 8 Class II specifications.

Also in that seminar, Maguire advised, “Until 25/40GBase-T processing capabilities are finalized, it’s too early to make a guarantee of 25/40GBase-T application support for any grade of cabling,” and that, “Performance to a draft Category 8 cabling specification is not the same as a 25/40GBase-T application support claim.”

We will continue to follow and report on the development of the IEEE 802.3bq specifications, as well as the possibility that the IEEE may initiate a 50GBase-T project. We also will follow and report on the TIA’s Category 8 specifications, including what happens once those specifications are finalized. When we learn of new information, we will post that information first at our website,

Patrick McLaughlin is our chief editor.

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