Network Infrastructure Blog

“40Gb/s throughput claims from cabling manufacturers are not the same as 40GBASE-T application support claims”

What is the status of the 40GBASE-T Standard?  40GBASE-T is currently under development by the IEEE 802.3bq 40GBASE-T Task Force formed in March of 2013.  The target publication date, as noted on the group’s Project Authorization Request, is February of 2016.  The Task Force has active liaisons with TIA and ISO/IEC to ensure that cabling requirements under development will support the application.

What is the difference between a 40Gb/s throughput and a 40GBASE-T application support claim?  Since the processing capabilities of 40GBASE-T PHY (i.e. the chip technology that delivers the Ethernet bit stream) aren’t yet defined, it’s impossible to guarantee 40GBASE-T application support for any media – including Siemon’s TERA® category 7_A cabling.  Many cabling experts, including Siemon, have performed 40Gb/s throughput analysis using hypothetical PHY capabilities to explore technical feasibility and justify the initiation of a higher speed Ethernet project.   However, this research can be misinterpreted as a statement about the ability of a system to specifically support the 40GBASE-T application. For example, Nexans, in conjunction with the University of Pennsylvania, theoretically demonstrated 40Gb/s throughput over 100 meters back in 2009. More recently, TE has released a white paper also claiming theoretical support of 40Gb/s.  While valuable for research purposes, these papers are not the same as making a 40GBASE-T application support claim because the assumptions used to make a 40Gb/s throughput statements have been based on analysis using noise cancellation levels that are far better than a real-world commercially viable PHY chipset can achieve.  In other words, statements that refer to a system’s ability to support “40Gb/s throughput” have no relevance on future compatibility with 40GBASE-T network equipment, simply because these claims and models are de-coupled from technical requirements that are yet to be specified by IEEE 802.3bq.

Are any manufacturers making a 40GBASE-T application support claim?  If the ratified 40GBASE-T Standard specifies compatibility with category 7_A or class F_A cabling, Siemon will provide retroactive and future 40GBASE-T applications assurance for all Siemon TERA category 7_A cabling systems that meet the length and topology constraints specified by that Standard. For example, if the IEEE 802.3bq Standard specifies compatibility with category 7_A or class F_A cabling having up to two connections and lengths up to 30m, we will provide 40GBASE-T applications assurance for installed Siemon TERA category 7_A cabling channels that fall within those implementation requirements.  No manufacturer is making an unconditional 40GBASE-T application support claim at this time.

When will Siemon provide a 40GBASE-T application support claim? Siemon will provide a 40GBASE-T applications support claim for specific cabling system types, lengths and topologies when Standards requirements that clearly define the cabling characteristics, baud rate, and other digital signal processing capabilities of the 40GBASE-T PHY are finalized.

Will category 8 cabling support 40GBASE-T?  When published, TIA and ISO/IEC category 8 cabling will support 40GBASE-T.  However, category 8 cabling requirements are currently in a high state of flux and claims of meeting draft category 8 performance specifications are not meaningful at this early stage of development.  Siemon cautions that a demonstration of performance to a draft category 8 cabling specification is not the same as a 40GBASE-T application support claim.

A whitepaper from the Communications Cable and Connectivity Association’s (CCCA) data center committee is a guide for data center professionals and IT managers. The whitepaper examines the many factors to consider when evaluating top of rack (ToR) and structured cabling configurations, including the impact of those configurations on total management; scalability and upgrades; interoperability; equipment, maintenance and cabling costs; port utilization; power consumption and cooling requirements.

The Communications Cable and Connectivity Association’s (CCCA) newly formed data center committee has developed a whitepaper that is a guide for data center professionals and IT managers.

The whitepaper, Navigating the Pros & Cons of Structured Cabling vs. Top of Rack in the Data Center, examines the many factors to consider when evaluating top of rack (ToR) and structured cabling configurations. Topics include the impact of those configurations on total management; scalability and upgrades; interoperability; equipment, maintenance and cabling costs; port utilization; power consumption and cooling requirements.

This whitepaper is the first of many planned contributions from the data center committee. “The pace at which data center hardware and space configuration changes is daunting. CCCA recognized both a need and an opportunity to help guide data center cabling decisions by providing the latest studies, options and expert views from the industry’s leading cable and connectivity manufacturers,” states Executive Director Frank Peri. “As with our other working groups, the goal of the CCCA data center committee is to add our voice to the development of industry codes, standards and other important resources.”

The Data Center committee plans an active and ongoing global communications program using a variety of venues. “The global data center environment is dynamic and challenging for those designing the cabling network,” adds Bob Carlson of the Siemon Company and Chair of the new committee. “Cabling systems design and topology choices have a significant impact on server and port utilization, operating efficiencies and even energy consumption. The new committee strives to provide information and insights that are relevant globally to assist design professionals and end users to make well-informed cabling decisions.”

CCCA is comprised of leading manufacturers, distributors and material suppliers who are committed to serve as a major resource for well-researched, fact-based information on the technologies and issues vital to the structured cabling industry. For information updates on data center and other timely industry topics, visit the association’s website at CCCA Association, sign up for the quarterly newsletter.

A New Work Item Proposal (NWIP) was agreed to be initiated by ISO/IEC JTC1 SC25 WG3 in February, 2013 at the Working Group’s Ixtapa, Mexico meeting.  The NWIP will include the development of 2 new cabling systems.  These systems will be based on the work currently being done in the development of the technical report entitled “ISO/IEC 11801-99-1 Guidance for balanced cabling in support of at least 40 GBit/s data transmission”.

It was agreed to name the two new systems Class I and Class II.  The new Classes will be included in the 3^rd edition of ISO/IEC 11801.  The Working Group has not yet decided exactly how to incorporate the new Classes into the 11801 series.  This will be discussed in more detail at the next meeting in September 2013.

To support the new systems, the components need to be named and specified.  The Working Group has decided that Category 8.1 components will be specified to support channel Class I.  Category 8.1 components shall be backwards compatible and interoperable with Category 6A components.  Category 8.2 components will be specified to support channel Class II.  These components will be an extension of Category 7A components.

The next meeting of ISO/IEC JTC1 SC25 WG3 will occur the week of September 30, 2013, in Sweden.  Brian Celella actively participates in the ISO/IEC JTC 1/SC 25/WG 3 Working Group and we will keep you advised when significant milestones are reached.

After debating the issue for three meetings cycles, the TIA TR-42.7 Copper Cabling Subcommittee adopted “category 8” as the name of their next generation balanced twisted-pair cabling system that is currently under development to support 40Gb/s transmission in a 2-connector channel over some distance up to at least 30 meters.  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. However, the real question 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 TIA specifies cabling systems up to category 6A performance, TIA chose not to adopt category 7 or 7_A as published by ISO/IEC.  TIA has now decided to call their next generation cabling system “category 8” to avoid confusion with published ISO/IEC category 7 and category 7_A 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 2 GHz whereas ISO/IEC specifies category 7_A requirements up to 1 GHz, the performance limits proposed for category 8 today do not meet or exceed category 7_A requirements up to 1 GHz.

So, herein lays the conundrum: category 8 is expected to have a different deployed channel topology and will not be a performance superset of category 7_A.  In fact, for every transmission parameter except return loss, ISO/IEC category 7_A channel and permanent link limits are more severe than those proposed by TR-42.7 for category 8 up to 1 GHz.  In the case of internal crosstalk parameters, the differences are significant: with category 7_A beating out category 8 performance by more than 20 dB!

So what about bandwidth of specification?  While category 7_A is currently specified to 1 GHz, new work items, such as the nearly finalized IEC 61076-3-104, 3rd edition standard for category 7_A connectors, are extending category 7_A performance characterization out to 2 GHz.  The situation of having two cabling specifications specified to 2GHz, with category 8 having much lower performance than category 7_A, 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 40 Gbit/s 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.

Until the processing capabilities of a 40 Gb/s Ethernet (40GBASE-T) application are finalized, it’s too early to guarantee 40GBASE-T application support distance for any media. However, fully-shielded category 7_A solutions, such as Siemon’s TERA™, 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 ISO/IEC is actively working on a project to characterize the capability of existing category 7_A cabling to support 40 Gbit/s data transmission.

The cover story of the latest edition of Processor magazine features an exciting story on Category 7A entitled “What About Category 7A Copper Cabling?”  In the article, you’ll learn how Siemon TERA remains today’s highest performing twisted-pair cabling system despite TIA’s new Category 8 nomenclature.

View the digital edition of Processor Magazine.