TIA 942 was the first data center cabling standard in the US. Many countries either follow or at least use its guidance. In TIA (View the Standards Informant Guide to TIA Standards), 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of 5 years during which time they are sometimes amended, and at the end of the 5 years they are revised, reaffirmed or rescinded.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