Network Infrastructure Blog

Posted on the public area of the newly formed IEEE 802.3 Next Generation BASE-T study group is an interesting contribution by Dan Dove of Applied Micro Circuits Corporation proposing three distinct cabling reach topologies for different applications in the data center.  What’s notable about this presentation is that a global leader in the Ethernet chip development industry is clearly expressing an opinion on the controversial topic of shielded versus UTP cabling.

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.

In a converged cabling system, balanced twisted-pair copper cabling is used to interface between BAS software and IP-enabled BAS devices with modular RJ-45 interfaces or controllers that communicate with multiple BAS devices.

Figure 1 depicts structured LAN cabling connections, represented by blue lines, from a BAS server to an IP-enabled camera and a controller in a basic converged cabling example.

Figure1: LAN Cabling Connections

The cabling from the controller to the BAS devices, represented by green lines, is typically application dependent low voltage wiring (e.g. two 18 AWG conductors).  In some cases, non‑IP BAS devices can accommodate both LAN cabling and low voltage cabling connections.

When the option is available, the use of LAN cabling for non-IP BAS device connections is always recommended to facilitate future migration to a fully IP‑based building automation system.

Note that a Standards-compliant structured cabling topology includes one or two patch panels in the telecommunications room, an equipment outlet in the work area, and an optional horizontal connection point located in a zone box to facilitate BAS device adds, moves, and changes.  For simplicity, these connection points are not shown in Figure 1.

Learn about ConvergeIT, a converged, IP-based intelligent building cabling system using a single, simplified structured cabling infrastructure for a smarter, greener building.

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The ANSI/TIA-606-B “Administration Standard for Telecommunications Infrastructure” published June, 2012.  This Standard specifies four classes of administration within buildings and between buildings based upon the complexity of the infrastructure being administered.  Administration requirements for commercial, industrial, residential, and data center premises are addressed.

Examples of recognized administration strategies include:

• assigning identifiers to components of the infrastructure
• specifying elements of information that make up records for each identifier
• specifying relationships between these records to access the information they contain
• specifying reports presenting information on groups of records, and
• specifying graphical and symbolic requirements

The four classes of administration are:

• Class 1 provides for the telecommunications infrastructure administration needs of a premises that is served by a single equipment room (ER)
• Class 2 provides for the telecommunications infrastructure administration needs of a single building or of a tenant that is served by single or multiple telecommunications spaces (e.g., an equipment room with one or more telecommunications rooms) within a single building
• Class 3 provides for the telecommunications infrastructure administration needs of a campus, including its buildings and outside plant elements
• Class 4 provides for the telecommunications infrastructure administration needs of a multi-campus/multi-site system

Copies of the Standard may be purchased from the IHS Standards Store.

TIA 942 was the first data center cabling standard in the US.  Many countries either follow or at least use its guidance.  In TIA, standards are written with a useful life of 5 years during which time they are sometimes amended, and at the end of the 5 years they are revised, reaffirmed or rescinded.  Since the original was published in 2005, it was time for the standard to be revisited.  Long overdue, the new version has published.  This paper will explain key differences in the standard.

First and foremost, much of the verbiage in the informative annex from the Uptime Institute Tier Levels has been removed or updated.  The problem is that people mistakenly were using the informative annex as a means to “certify” a data center to a Tier Level.  As an informative annex by definition, it is NOT part of the standard unless it is referenced elsewhere in the standard.  The only place that occurs in the new standard is referring to Tier 4 cabling and the requirements that primary and secondary cabling take diverse pathways.  This assures that a pathway fault will not endanger both cabling links.

Category 3 and 5e are no longer acceptable for horizontal cabling, they are allowed for voice backbone.  Category 6 is the minimum recognized horizontal copper cabling, with 6A the minimum recommended.  Note:  There is a power advantage to 6A channels under 30m when running 10GBASE-T.  Built into the IEEE 10GBASE-T standard is a technology called short reach mode.  Short reach mode only operates on channels under 30m, however this ONLY works on 6A and above cabling.  With current chips, the savings is approximately 1.5W per port.  According to Emerson/Liebert studies, 1W saved at the server port equates to 2.84W throughout the remaining systems.  It is very easy to segment the data center into distribution areas under 30m to take advantage of this power savings.

On the fiber side of things, OM1 and OM2 are no longer recognized.  OM3 is the minimum recognized with OM4 being the minimum recommended.  While the only advantage today of OM4 over OM3, future technologies are expected to fully take advantage of the superior performance of OM4.  LC is the approved connector for two strand applications, and the MTP/MPO connector for multi-strand applications.  Point to point cabling (such as those used in top of rack switching) should only be in close proximity and any unused cables must be removed.

An MTP connector is an MPO connector with stainless steel alignment pins to assure better mating.  An MPO connector is not an MTP.  These connectors are available in either 12 or 24 strands with 12 strands being the most popular.  This echoes the 40GbE and 100GbE standards published in IEEE that use multiple strands for parallel transmission over multimode fiber.  Single mode fiber will continue to use 2 strands.   The previous standard included a max distance for horizontal fiber, that restriction has been removed and is now based on the application.

The language referring to the TIA 568 series of standards, and the 606 (Administration), 569 (Pathways and Spaces), and 607 (Grounding and Bonding) have been removed as text and are now referenced in 942-A allowing a single set of edits in future revisions.   The previous addendums (942-1 and 942-2) have been incorporated into the main body of the standard.

A new distribution area called an Intermediate Distribution Area now exists as needed between the Main Distribution Area and Horizontal Distribution Areas.   These are designed for the larger data centers and multi-level switching environments.  The Main Distribution area is the only required area.  Multi-floor data centers must have at least one Horizontal Distribution Area per floor.  Previously defined Equipment Distribution Areas are now called Equipment Outlets in sync with the ISO data center standard.   Active equipment is no longer allowed in the Zone Distribution Areas.

A new section on Energy Efficiency has been added and recommends removal of abandoned cable under the floor (also a code requirement in the US), properly sizing pathways and spaces for growth, and routing cabling so as to not obstruct airflow.  In some raised floor environments, overhead systems may improve airflow.

Data Center cabinets with isolated airflow can help improve room efficiency such as chimneys or ducted returns.  Cabinets should be fitted with blanking panels and penetrations both in the floor and in cabinets should be fitted with brush guards.

There is a recommendation to monitor power consumption in the cabinet as well as in the room.  This is becoming a common practice in data centers as a means to measure efficiencies.  In some cases it may be beneficial to segment equipment with different energy requirements, for instance, high density areas.  This allows supplemental cooling to be added to those high density areas as opposed to the entire room.

Room temperature/humidity recommendations are now harmonized with ASHRAE as follows.  Max room temperature is now 81°F (27°C).  It is important to be careful when raising the temperature to assure that the server fans do not negate the energy savings of a warmer room.  This is more a problem on legacy equipment, but can exist in new equipment as well.    The minimum recommended temperature is set to 64°F (18°C).  Maximum relative humidity is 60% with a max dew point of 59°F (15°C).  The recommendations of ASHRAE take into account many of the newer cooling methods including air side economizers, water side economizers, etc.

There are informative annex’s included as follows:

Annex A :  Cabling Design Considerations

Annex B:  Telecommunications Infrastructure Administration

Annex C:  Access Provider Information

Annex D:  Coordination of Equipment Plans and Other Engineers

Annex E:  Data Center Space Considerations

Annex F:  Site Selection

Annex G:  Amended Uptime Data Center Infrastructure Tiers

Annex H:  Data Center Design Examples

Annex I:  Bibliography