While the proposed ANSI/TIA-568-C.2-1 project to create specifications for a cabling system targeted to support 40Gbps transmission has been under development since early 2011, it wasn’t until late 2012 that the TIA TR-42.7 Copper Cabling Subcommittee adopted the ‘category 8’ naming convention. The issue of what to call this new system was a subject close to the hearts of many subcommittee members, and both proponents and opponents of the new name argued tenaciously for their positions for three meeting cycles before consensus was reached. The real question, however, is just how much confusion the name category 8 is going to cause for the industry?

Traditionally, cabling categories are supersets of each other – meaning that a higher category of cabling meets or exceeds all of the electrical and mechanical requirements of a lower category of cabling and is also backwards-compatible with the lower-performing category. While the TIA specifies cabling systems up to category 6A performance, it chose not to adopt category 7 or 7A as published by ISO/IEC. Instead, the TIA has decided to call its next-generation cabling system category 8 to avoid confusion with published ISO/IEC category 7 and category 7A standards, which are indeed supersets of each other and of category 6A.

While it’s true that the currently proposed category 8 specifications tentatively describe transmission performance up to 2GHz, whereas ISO/IEC specifies category 7A requirements up to 1GHz, the performance limits proposed for category 8 today do not meet or exceed category 7A requirements up to 1GHz.

Does Category 7A beat category 8?
So herein lies the conundrum: category 8 is expected to have a different deployed channel topology and will not be a performance superset of category 7A. In fact, for every transmission parameter except return loss, ISO/IEC category 7A channel and permanent link limits are more severe than those proposed by TIA TR-42.7 for category 8 up to 1GHz. In the case of internal crosstalk parameters, the differences are significant; with category 7A beating category 8 performance by more than 20dB. So what about bandwidth of specification? While category 7A is currently specified to 1GHz, new work items, such as the nearly finalised IEC 61076-3-104, third-edition standard, are extending category 7A connector performance characterization out to 2GHz. The situation of having two cabling specifications specified to 2GHz, with category 8 having much lower performance than category 7A, is really going to create confusion.

What to name next-generation cabling systems is not just a TIA issue; ISO/IEC also faced the same challenge with their new project to define two new grades of cabling (shielded and fully shielded) to support 40Gbps data transmission. ISO/IEC recently adopted class I to describe cabling constructed from shielded modular RJ-45-style category 8.1 components and class II to describe cabling constructed from fully shielded category 8.2 components. In TIA’s defense, alternative naming options would have been likely to result in a departure from the familiar category numbering convention, and that may have had unpleasant implications. So, although TIA’s decision was not made in haste, it was considered by some to be the least unpalatable choice from a handful of unattractive options.

Breaking the rules 
The industry needs to understand that the once golden rule of higher categories being supersets of lower categories has been broken. Furthermore, until the processing capabilities of a 40bE (40GBASE-T) application are finalized, it’s too early to guarantee 40GBASE-T application support distance for any media. However, fully shielded category 7A solutions remain the highest-performing twisted-pair cabling system commercially available today. Not only do these solutions provide higher EMI/RFI immunity and more flexible cable-sharing capabilities than RJ-45 style solutions, but the ISO/IEC is actively working on a project to characterize the capability of existing category 7A cabling to support 40Gbps data transmission.