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 http://www.cccassoc.org, sign up for the quarterly newsletter, check the Communications Cable & Connectivity LinkedIn group, and CCCA’s YouTube page.

Three new Physical Layer implementations will be defined as follows:

100GBASE-CR4: IEEE 802.3 Physical Layer specification for 100 Gb/s using 100GBASE-R encoding and Clause 91 RS-FEC over four lanes of shielded balanced copper cabling, with reach up to at least 5 m

100GBASE-KP4: IEEE 802.3 Physical Layer specification for 100 Gb/s using 100GBASE-R encoding, Clause 91 RS-FEC, and 4-level pulse amplitude modulation over four lanes of an electrical back-plane, with a total insertion loss up to 33 dB at 7 GHz

100GBASE-KR4: IEEE 802.3 Physical Layer specification for 100 Gb/s using 100GBASE-R encoding, Clause 91 RS-FEC, and 2-level pulse amplitude modulation over four lanes of an electrical back-plane, with a total insertion loss up to 35 dB at 12.9 GHz

The IEEE 802.3 100 Gb/s Backplane and Copper Cable Call-For-Interest Consensus Presentation can be found here: http://www.ieee802.org/3/100GCU/public/nov10/index.html

The current focus of the IEEE P802.3bj 100 Gb/s Backplane and Copper Cable Task Force  is resolution of comments received during Working Group ballot review of their draft.

The Project Authorization Request (PAR), approved on September 10, 2011, can be found here: http://www.ieee802.org/3/bj/P802.3bj_1212.pdf

The project objectives, adopted approved in July 2011 with changes through July, 2012, (refer to:  http://www.ieee802.org/3/bj/objectives_0712.pdf) are as follows:

• Support full-duplex operation only
• Preserve the 802.3 / Ethernet frame format utilizing the 802.3 MA
• Support a BER of better than or equal to 10-¹² at the MAC/PLS service interface
• Define a 4 lane PHY for operation over a printed circuit board backplane with a total channel insertion loss of <= 35 dB at 12.9 GHz
• Define a 4 lane PHY for operation over a printed circuit board backplane with a total channel insertion loss of <= 33 dB at 7.0 GHz
• Define a 4-lane 100 Gb/s PHY for operation over links consistent with copper twin-axial cables with lengths up to at least 5m
• To define optional Energy-Efficient Ethernet operation for 100G Backplane and Twinaxial cable PHYs specified in P802.3bj
• To define optional Energy-Efficient Ethernet operation for 100GBASE-CR10
• To define optional Energy-Efficient Ethernet operation for 40GBASE-CR4 and 40GBASE-KR4

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.

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.

View the digital edition of Processor Magazine.

The IEEE 802.3 Extended EPON Call-For-Interest Consensus Presentation can be found here: http://www.ieee802.org/3/EXTND_EPON/public/1107/CFI_02_0711.pdf

The current focus of the IEEE 802.3bk Extended EPON Task Force is resolution of comments received during Sponsor ballot review of their draft.

The Project Authorization Request (PAR), approved on March 29, 2012 with changes from October 29, 2012, can be found here: http://www.ieee802.org/3/bk/P802_3bk_PAR_291012.pdf

The project objectives, adopted on November 10, 2011, (refer to:  http://www.ieee802.org/3/bk/ExEPON_Objectives_approved.pdf) are as follows:

• Support subscriber access networks using point-to-multipoint topologies on SM optical fiber
• EPON PHY(s) to have a BER better than or equal to 10^-12 at the MAC/PLS service interface
• Provide physical layer specifications:
• for 1G-EPON supporting a downstream channel insertion loss of 29 dB, compatible with PR(X)30 upstream channel insertion loss
• for 1G-EPON supporting a split ratio of at least 1:64 at a distance of at least 20 km
• for 10G-EPON, supporting a split ratio of at least 1:64 at a distance of at least 20 km
• Changes to be confined to the PMD layer; PCS and MPCP are to be reused as is
• Maintain coexistence among 1G-EPON and 10G-EPON (i.e. support the same loss budget classes for 1G-EPON and 10G-EPON)

• 100 Gb/s transmission using a four-lane electrical interface (8 fibers total) for operation over multimode optical fiber cabling
• 100 Gb/s transmission using four-wavelength CWDM or PCM4 (2 fibers total)  or 4 x 25 Gb/s serial (8 fibers total) for operation over singlemode optical fiber cabling
• 100 Gb/s four-lane electrical interface between host ICs and optical modules for use in electrical backplanes
• 40 Gb/s transmission (2 fibers total) over extended reach (> 10 km) singlemode fiber optic cabling

The rapid growth of server, network, and internet traffic is driving the need for higher data rates, higher density, and lower cost optical fiber Ethernet solutions, especially in the data center space. The 100 Gb/s optical fiber Ethernet applications specified in IEEE 802.3ba include a ten-lane electrical interface (20 fibers total) for operation over multimode optical fiber cabling (100GBASE-SR10) and a 4 x 25 Gb/s wavelength division multiplexed solution (2 fibers total) for operation over singlemode optical fiber cabling (100GBASE-LR4).  Advances in technology now allow the specification of new 100 Gb/s Physical Layer types with reduced lane count and complexity to reduce cost.   In addition, this new project adds two new Ethernet applications that had not been previously specified for 100 Gb/s Ethernet operation over electrical backplanes and 40 Gb/s Ethernet operation over extended reach (> 10 km) singlemode fiber optic cabling.

The IEEE 802.3 Next Generation 100 Gb/s Optical Ethernet Call-For-Interest Consensus Presentation can be found here: http://www.ieee802.org/3/100GNGOPTX/public/jul11/CFI_01_0711.pdf

The IEEE 802.3 Extended reach 40 Gb/s Optical Ethernet Call-For-Interest Consensus Presenation can be found here: http://www.ieee802.org/3/100GNGOPTX/public/CFI_extended40Gb/40G_ER_CFI.pdf

The current focus of the IEEE 802.3bm 40 Gb/s and 100 Gb/s Fiber Optic Task Force is the development of a draft for Task Force review.

The Project Authorization Request (PAR), approved on May 10, 2013, can be found here: http://www.ieee802.org/3/bm/P802.3bm_May2013.pdf

The project objectives, adopted on November 15, 2012, (refer to: http://www.ieee802.org/3/bm/P8023bm_Objectives_1112.pdf) are as follows:

• Support full duplex operation only
• Preserve the 802.3 / Ethernet frame format utilizing the 802.3 MAC
• Preserve minimum and maximum Frame Size of current 802.3 standard
• Support a BER better than or equal to 10^-12 at the MAC/PLS service interface
• Provide appropriate support for OTN
• Define re-timed 4-lane 100G PMA to PMA electrical interfaces for chip to chip and chip to module applications
• Define a 40 Gb/s PHY for operation over at least 40 km of SMF
• Define a 100 Gb/s PHY for operation up to at least 500 m of SMF
• Define a 100 Gb/s PHY for operation up to at least 100 m of MMF
• Define a 100 Gb/s PHY for operation up to at least 20 m of MMF
• Specify optional Energy Efficient Ethernet (EEE) for 40 Gb/s and 100 Gb/s operation over fiber optic cables

ANSI/TIA-1183 “Measurement Methods and Test Fixtures for Balun-Less Measurements of Balanced Components and Systems” was developed by the TIA TR-42.7  Copper Cabling Subcommittee and published in August, 2012.  This Standard is intended to be used as an independent testing reference and describes methods and fixtures that support laboratory measurement of all differential mode, mixed mode, and common mode transmission parameters up to 1 GHz.   The primary benefit of using the test methods and fixtures described in this Standard is the elimination of balun transformers traditionally used for impedance matching between the device under test (DUT) and the measurement equipment.

Removing the balun transformers from the test set-up allows the collection of transmission measurements up to the frequency band of the network analyzer and expands the allowable measurement modes (i.e. differential mode, mixed mode, and common mode).   This measurement flexibility enables testing of mixed mode parameters such as balance (e.g. TCL and TCTL) and cross-modal crosstalk coupling without reconfiguration of the DUT or the measurement setup.

ANSI/TIA-1183  Content

• Test configurations
• Fixtures and setup
• Port terminations
• Reference loads for calibration and termination
• Calibration
• Example test fixture assemblies
• Informative Annexes addressing Derivation of Mixed Mode Parameters from Four Port S Parameter Measurements,  Impedance Transformation Calculations, Cabling Standards and Termination Impedances for Differential Cabling Systems, Port Identification and Nomenclature, and De-embedding Balunless Test Fixtures for Measuring 16-Port Differential Devices

Example Balun-Less Test Fixture with Rigid SMA Coaxial Connectors

In his contribution, Mr. Dove proposes using shielded cables for support of Top-of-Rack (server to switch) applications because the media’s reduced echo and near-end crosstalk loss, reduced transmit power requirements, and virtually zero alien crosstalk support signal transmission with a simplified electromagnetic immunity (EMI) chip design.  Mr. Dove also questions the use of UTP cables to support the structured cabling End-of-Row topology (server to switch, switch to switch, and switch to core switch) connections because transmission over UTP media requires a more complex EMI chip design, introduces challenges related to additional return loss and near-end crosstalk loss, needs higher transmit power, and requires attention to the disruptive effects of alien crosstalk.

Points associated with shielded cabling:

• Simplifies EMI design
• Reduces Echo/NEXT challenges of multiple connectors
• Reduces TX power requirement
• Virtually eliminates ANEXT

Points associated with UTP:

• More complex EMI design
• Requires Echo/NEXT challenges of multiple connectors
• Increases TX power requirement
• Requires attention to ANEXT

Is this finally the tipping point for shielded cabling?

You can find Mr. Dove’s contribution here on IEEE802.org to explore this issue further.

ISO/IEC TR 29125 Edition 1.0: “Telecommunications Cabling Requirements for Remote Powering of Terminal Equipment” was developed by subcommittee 25: Interconnection of information technology equipment, of ISO/IEC joint technical committee 1: Information technology.  ISO/IEC TR 29125 Edition 1.0 was published September 2010. 

ISO/IEC TR 29125 Edition 1.0 Contents

• Conformance
• Cabling Selection and Performance
• Installation Conditions
• Transmission Requirements
• Remote Power Delivery Over Balanced Cabling
• Connecting Hardware
• Annex on Mitigation Considerations for Installed Cabling

This full standard is available for purchase on the IEC Webstore here.