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Data centre standard OK’d

Long-awaited TIA-942 is expected to fulfill a recognized need for infrastructure requirements.

April 1, 2005  

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The new data centre standard was ap-proved for publication at the last Telecommunications Industry Association (TIA) TR 42.1 subcommittee meeting in February. It should be available shortly from Global Engineering Documents at

“Telecommunications Infrastructure Standard for Data Centres” TIA-942 gives a good understanding of all aspects of data centre design including the facility planning, the cabling system and the network design. The standard provides design requirements for both the cabling and the physical infrastructure (pathways and spaces).

It includes informative annexes on a wide variety of subjects related to the data centre design such as data centre sizing and site selection, cabling system infrastructure administration, architectural and structural considerations, security and fire protection guidelines, electrical and mechanical systems, application distances, and access provider coordination and demarcation. In addition, the standard provides specifications for data centre reliability which are organized into four tiers where Tier 1 has no redundancy and Tier 4 provides the highest degree of fault tolerance.

Star topology

A data centre is configured in a star topology which includes the following telecommunications spaces: entrance room, main distribution area (MDA), horizontal distribution area (HDA), zone distribution area (ZDA) and equipment distribution area (EDA).

The entrance room is the space where the data centre structured cabling system interfaces with campus cabling systems and the access provider cabling systems.

A data centre may have multiple entrance rooms for redundancy or to avoid exceeding maximum circuit length restrictions. The standard provides guidance regarding maximum circuit lengths in data centres.

MDA includes the main cross-connect (MC), which is the central point of distribution for the data centre structured cabling system The MDA typically houses core routers and switches for the data centre LAN and SAN infrastructure.

Distribution point

HDA includes a horizontal cross-connect (HC), the distribution point for horizontal cabling to equipment distribution areas. The HDA typically houses LAN switches, SAN switches, and KVM switches for the equipment in the equipment distribution areas.

There may be an optional interconnection point within the horizontal cabling, called a zone distribution area (ZDA) between the horizontal distribution area and the equipment distribution area to allow frequent reconfiguration and flexibility.

EDA is the space allocated for end equipment, including computers and telecommunications equipment. Horizontal cabling is terminated in the EDA on outlets, which are typically located on patch panels mounted in an equipment cabinet or rack.

The standard recognizes that an EDA may include equipment that are directly cabled to each other — for example, switches and blade servers or servers and peripherals.

Cabling Media: The standard recognizes multiple media types to support a wide variety of applications, but it recommends that the highest capacity cabling media be used for new installations to maximize the flexibility and useful life of the data centre cabling infrastructure.

The recognized media are 100-ohm twisted-pair cable (ANSI/TIA/EIA-568-B.2); category 6 is recommended (ANSI/TIA/EIA-568-B.2-1); multimode optical fiber cable (ANSI/TIA/EIA-568- B.3); 50/125 micron 850 nm laser optimized multimode fiber is recommended (ANSI/TIA-568- 16 B.3-1); singlemode optical fiber cable (ANSI/TIA/EIA-568-B.3); 75-ohm (734 and 735 type) coaxial cable (Telcordia Technologies GR-139-CORE) and coaxial connectors (ANSI T1.404).

These cables and connectors are recommended to support T-3, E-1, and E-3 circuits.

It recognizes a variety of cabling pathways, including the access floor (raised floor) systems and overhead cable tray systems that are typically used in data centres.

Equipment rows are recommended to be arranged in an alternating pattern, with the fronts of cabinets/racks facing each other to create hot and cold aisles.

Equipment should be placed with “cold” air intake at the front of the cabinet or rack, and “hot” air exhaust out the back.

This is the culmination of a lot of engineering effort from the members of the task group who participated in formulating the document.

Special thanks to Chris Diminico and Jonathan Jew, the co-chairs of the task group, and to Julie Roy as the editor, for their contribution in developing the document.

Paul Kish is Director, IBDN Systems & Standards at Belden CDT Networking Division (NORDX). He is also vice chair of the TR-42 engineering committee.

Disclaimer: The information presented is the author’s view and is not official TIA correspondence.