Figure 1


Networks continue to evolve and grow. The need for more and more storage continues, even in a challenging economic environment. Infonetics recently published their forecast for storage area network switch and adapter port growth. Figure 1 shows that even though 2009 was a down year, the next five years are predicted to have very good growth. Also, next-generation data centers will migrate to higher speeds like 40G and 100G.

Figure 2


As data centers grow and migrate to higher speeds, backbone cabling becomes a key design area. The backbone cabling system is a key component that influences the design and functionality of all the other components in the data center. In the past, most backbone cabling systems consisted of cables that were terminated with standard two-fiber duplex connectors. Now many systems are moving to cabling systems that use 12-fiber and, in the future, 24-fiber connectors.


TIA-942, Telecommunications Infrastructure Standard for Data Centers, was released in April 2005. The purpose of this standard is to provide information about the factors that should be considered when planning and preparing the installation of a data center or computer room.

TIA-942 defines the main elements of a data center as the main distribution area (MDA), the horizontal distribution area (HDA), the zone distribution area (ZDA), and the equipment distribution area (EDA). The MDA includes the main cross-connect, which is the central point of distribution for the data center structured cabling system and may include a horizontal cross-connect when equipment areas are directly served from the MDA. The HDA serves equipment areas, and EDAs are allocated for end equipment (figure 2).

Figure 3


Systems today require duplex connections for Ethernet systems up to 10G and fiber-channel systems up to 16G. In the future, 40G and 100G systems will require parallel connectivity. Planning the type of cabling infrastructure that can migrate to these speeds will be critical in next-generation data center design.

Cabling Systems Defined

Most legacy networks use a base-2 cabling system (figure 3). In this type of cabling infrastructure, the backbone/horizontal cabling traditionally is broken out into two-fiber duplex connectors. These interconnect to the electronics, which use two-fiber duplex transmit/receive technology.


Figure 4


Today, data center infrastructures are migrating to a backbone cabling system that uses array connectors, or MPO connectors, that allow for greater connectivity density in interconnect and cross-connect hardware (figure 4). In this type of cabling infrastructure, the backbone/horizontal cabling is traditionally broken out into multi-fiber array connectors.

These array connectors break out into duplex connectors in the MDA, HDA, ZDA, and EDA or anywhere they need to terminate into electronics (need to break out to duplex connectors to perform the cross-connect in the MDA). A module or harness is used in these systems to transition from a 12-fiber MPO connector to six duplex connectors (figure 5).

Figure 5


Like simplex and duplex connectors and adapters, MPO connectors and adapters are keyed to ensure the proper orientation is maintained when connectors are mated. With MPO connectors, this keying establishes the orientation of one fiber array in one connector relative to the array in the mating connector. Next-generation cabling infrastructure will utilize 24-fiber array MPO connectors for greater hardware density.

Like 12-fiber MPO connectors and adapters, 24-fiber MPO connectors and adapters are keyed to ensure the proper orientation is maintained when connectors are mated. The 24-fiber MPO connector also has the same “footprint” as the 12-fiber MPO connector. This is very important when migrating a network from 10G to 40G and 100G.

Base-12 and Base-24 Cabling

Using a base-12 or base-24 cabling system is shown in figure 6. This type of system uses the benefits of the high-density MPO connector to connect from the MDA to the HDA. The key components in this system are the trunk cables and the modules/harnesses. The modules/harnesses are needed to convert from a base-12 or base-24 connector back to a duplex connector. Duplex connectivity is needed for most applications running at speeds of 16G or less.

Figure 6


Next-generation data centers will use 40G and 100G solutions in the data center. These types of applications will require parallel optics to connect switches together. See figures 7 and 8.

The 40G and 100G technical requirements are defined in the recent sponsor ballot approved IEEE 802.3ba document. It defines the parameter for 40G and 100G communications across OM3 and OM4 multimode fiber. For 40G, the IEEE defines 40GBASE-SR4 (parallel optics) as:

  • 100 m on OM3 – 10G on four fibers per direction
  • 150 m on OM4 – 10G on four fibers per direction

Figure 7


IEEE defines 100GBASE-SR10 (parallel optics) as:

  • 100 m on OM3 – 10G on 10 fibers per direction
  • 150 m on OM4 – 10G on 10 fibers per direction

Figure 8


The next area to analyze is how each of these cabling systems (base-12, base-24) migrates from the duplex world of serial circuits to the parallel world of 40G and 100G. Figure 9 shows the migration paths on a base-12 cabling infrastructure.

Figure 9


Figure 9 shows that the first step in migrating from a 10G network to a 40G network is accomplished by removing the base-12 to base-2 module and replacing it with a base-12 to base-12 adapter panel. An adapter panel is different from a module in that it does not break out a 12-fiber connector into a two-fiber duplex connector. Instead, it mates two 12-fiber MPO connectors to create the 40G link. In this scenario, a 12-fiber MPO to 12-fiber MPO jumper is installed. Based on the IEEE specifications for 40G, eight fibers out of the 12 are used to create a fiber utilization efficiency of 67 percent.

Figure 10


Moving to a 100G network will require the use of a 24-fiber MPO connector to create the circuit. This creates a network infrastructure challenge, specifically how to connect a 24-fiber connector into a base-12 cabling system. Use a dual 12-fiber MPO to 24-fiber MPO patch cord. This will enable the end-user to come out of the 100G port with 24 fibers and split them into two 12-fiber circuits. This will create an easy use of the base-12 cabling infrastructure and achieve a fiber utilization of 83 percent. Moving the same example to a base-24 cabling infrastructure is shown in figure 10.



Structured cabling is an important part of data center planning. The use of base-12 and base-24 cabling can greatly improve the design process and provide greater infrastructure efficiencies. Proper planning needs to be taken into account when migrating these types of cabling infrastructures to 40G and 100G networks.