The standard covers the following
• Site space and layout
• Cabling infrastructure
• Tiered reliability
• Environmental considerations
Site Space and Layout
Proper space allocation for a data centre starts with ensuring that space can be easily reallocated tochanging environments and growth. Designers must strike a balance between acceptable initial deploymentcosts and anticipated space required in the future.The data centre should be designed with plentyof flexible “white space,” empty space that can accommodate future racks or cabinets.
The spacesurrounding the data centre must also be considered for future growth and planned for easy annexation.A large part of TIA-942 deals with facility specifications. The standard recommends specific functional areas,which helps to define equipment placement based on the standard hierarchical star topology design for regularcommercial spaces. Designing a data centre with these functional areas anticipates growth and helps createan environment where applications and servers can be added and upgraded with minimal downtime anddisruption. According to TIA-942, a data centre should include the following key functional areas:
One or More Entrance Rooms
This is the location for access provider equipment and demarcation points, as well as the interface withcampus cabling systems. The Entrance Room may be located either inside or outside the computer room, theportion of the data centre that houses data processing equipment. The standard recommends locating theentrance room outside of the computer room for better security. When located within the computer room, the Entrance Room should be consolidated with the MDA. It is possible that provider’s cabling distances may require multiple Entrance Rooms for larger data centres.
Main Distribution Area (MDA)
Similar to an MDF, the MDA is a centrally located area that houses the main cross-connect as well as corerouters and switches for LAN and SAN infrastructures. The MDA may include a horizontal cross-connect (HC) for a nearby equipment distribution area. Thestandard requires at least one MDA and specifiesinstalling separate racks for fibre, UTP, and coaxialcable in this location.
One or More Horizontal Distribution Areas(HDA)
Similar to a TR, the HDA serves as the distributionpoint for horizontal cabling and houses cross-connectsand active equipment for distributing cable to theequipment distribution area. Like the MDA, thestandard specifies installing separate racks for fibre, UTP,and coaxial cable in this location. It also recommendslocating switches and patch panels to minimise patchcord lengths and facilitate cable management. TheHDA is limited to 2000 connections, and the numberof HDAs is dependent on the amount of cabling andoverall size of the data centre.
Equipment Distribution Area (EDA)
Horizontal cables are typically terminated with patchpanels in the EDA, the location of equipment cabinets
and racks. The standard specifies installing racks andcabinets in an alternating pattern to create “hot”and “cold” aisles, a configuration that effectivelydissipates heat from electronics (see Environmental Considerations for a discussion on cooling and hotaisle/cold aisle configuration).
Zone Distribution Area (ZDA)
The ZDA is an optional interconnection point in thehorizontal cabling between the HDA and EDA. The ZDA
can act as a consolidation point for reconfigurationflexibility or for housing freestanding equipment like mainframes and servers that cannot accept patch panels.Only one ZDA is allowed within a horizontal cabling runwith a maximum of 288 connections. The ZDA cannotcontain any cross-connects or active equipment.
Backbone and Horizontal Cabling
Within the data centre, backbone cabling providesconnections between MDA, HDAs, and EntranceRooms while horizontal cabling provides connectionsbetween HDAs, ZDA, and EDA. Optional backbonecabling can be installed between HDAs for redundancy.Each functional area must be located in such a way toprevent exceeding maximum cable lengths for bothbackbone and horizontal cabling.
The TIA-942 standard also specifies maximum backboneand horizontal cabling distances based on the cablingmedia and applications to be supported in the datacentre. Backbone fibre optic cabling is typically limitedto 300m while horizontal copper cabling is limited to100m. However, for small data centres where the HAD is combined with the MDA, horizontal fibre cabling mayextend to 300 metres.The TIA-942 standard provides several requirementsand recommendations for cabling management. Thedata centre must be designed with separate racksand pathways for each media type, and power and communications cables must be placed in separate pathways or separated by a physical barrier. Adequatespace must be provided within and between racks andcabinets and in pathways for better cable management,bend radius protection, and access. For example, thestandard requires a minimum of 3 feet in rows (4 feetrecommended) and recommends aligning racks and
• Single path for power and cooling disruption, includes
redundant components (N+1)
• Includes raised floor, UPS, and generator
• Takes 3 to 6 months to implement
• Annual downtime of 22.0 hours
• Maintenance of power path and other parts of the infrastructure require a processing shutdown
Building on existing TIA-568 and 569 standards, theTIA-942 standard specifies a generic, permanent
telecommunications cabling system and providesspecifications for the following recognised cabling media:
• Standard singlemode fibre
• 62.5 and 50μm multimode fibre
• Laser-optimised 50μm multimode fibre (recommended)
• 75-ohm coaxial cable (recommended for E-1, E-3,
and T-3 circuits)
• 4-Pair Category 6 UTP and ScTP cabling
(Cat 6* recommended)
*NOTE: Augmented Category 6 was not a released standardat the time that TIA-942 was ratified. It is expected that future
revisions of TIA-942 will specify Augmented Category 6 as thepreferred UTP cable for data centres.
TIA-942 recommends the use of laser-optimised 50μmmultimode fibre for backbone cabling because of its
capability of supporting higher network speeds overlonger distances while being more cost-effective to
implement than singlemode fibre.