Structured Communications Cabling
April 01, 2009
By Anthony Jamsek, Syska Hennessy Group
Appeared in Mission Critical
Change is the only constant in today’s data center. And chances are that this change will affect the cable plant that provides connectivity within the data center. How much a change will affect cabling depends on the design of the cabling. Implementation of a structured cable plant will benefit day-to-day operations—with regards to cost, management, flexibility, and reliability.
A well-designed cabling system consists of a least one main distribution area (MDA) and one or several horizontal distribution areas (HDA). The MDA is the location of the core network equipment and the termination point for the backbone cables. The HDA is the location of the network distribution equipment and horizontal cabling terminations.
This structured type of design has many benefits. The cable plant and associated pathways and spaces can be fully and concurrently designed alongside the data center, allowing for its integration into the overall plan of the data center. The cable tray and termination racks and cabinets can be coordinated with other infrastructure systems, such as HVAC and power and architectural features.
Installing cabling during construction creates efficiencies because multiple crews can pull, terminate, and test the cabling while the other trades install HVAC and power equipment around it. Timing cable installation also means that costly data processing equipment cannot be damaged at this stage because it hasn’t been deployed. Timing cable installation also minimizes planning for the deployment of data processing equipment and makes the process more efficient since only intra-rack patch cords will need to be installed for final connectivity. A construction manager specializing in this type of multi-trade coordination and scheduling can manage the installation.
A structured cable plant leads to improved cable pathway utilization. A structured cabling system isolates the higher-density cabling areas within an HDA, so that the high-density copper horizontal cable runs from the HDA to the server cabinets while fiber backbone cable runs between the MDA and HDA. This means that only the smaller and less numerous backbone cables traverse the data center in the cable tray, and no patch cords.
High-density server areas can be isolated so that cable trays can be smaller, which makes them easier to manage. In addition, cable routes can be planned so the cable tray is properly sized. And since patch cords are kept outside of the cable tray, there is less chance of damage to them, particularly to fiber patch cords.
A structured cable plant design further allows for more flexibility and scalability for expansion. To expand data center capability, an HDA and associated backbone cables from the MDA can simply be added. In this scenario, the operational areas of the data center have less exposure to new construction and less of a chance that an outage will occur due to damage. New horizontal cables will be isolated to the HDA area, and only the new backbone cables would run in operational areas.
Management & Administration
Planning cabling during the design phase of the data center allows for systematic labeling, testing, and documentation of all cables, patch panels, racks. and cabinets. These steps facilitate later changes within the data center and allow for better documentation of the cable plant through patch schedules and other database tracking programs. In addition, the documentation and the logical layout of the facility help the technical staff managing the data center more proficiently and makes the maintaining the data center becomes easier as well.
Whether for an individual server
installation or a complete technology upgrade, a structured cable
plant can easily accommodate changes to the data center. Since
horizontal runs are supported in the cable tray and terminated on
patch panels at both ends, change is as simple as removing a patch
cord, swapping out or adding the new equipment, and installing a
patch cord to the new equipment. There is no need to run new cables
in the cable tray. That means less risk of a service outage, since
the horizontal cables are essentially fixed and will not have to be
Similarly, the structured cable plant also makes large deployments easier to plan. Since there is no need to run new cables, more equipment can be installed during the planned service maintenance windows and deployment can be completed sooner with less risk to existing equipment.
Cost of Implementation & Maintenance
Since a structured cable plant’s
design is modular and cabling is installed during construction, work
can be performed during regular hours, which translates into cost
savings because changes do not have to be made during off-hours at
premium time labor rates. Furthermore, if the cable plant is
installed during construction, its cost can be incorporated into the
capital expenditures as a small percentage of the overall cost of the
Data centers are becoming larger, using more power and housing more high-density equipment. As these factors and the need for reliability grow, so do the requirements for connectivity to the data processing equipment. With more and more blade server deployments and a larger utilization of a SAN environment, the volume of cabling infrastructure within the data center is increasing.
Case in Point
A structured cable plant was designed and installed in a mid-size data center for a large financial firm. The client only knew the generic requirements for the equipment that was going to be installed in the server cabinets within the data center. Therefore the design approach had to be flexible enough to accommodate a worst-case scenario but also keep in mind cost, cabling density, and aesthetics.
The mechanical and electrical infrastructure of the data center was designed to support a variety of equipment, including blade servers, traditional servers, a tape library, network equipment, and a storage area network (SAN). The equipment was grouped based on power and cooling requirements. In the same way, the cable plant was designed based on this approach, with the rows of equipment designated for high-density servers getting more cabling than the rows designed for lower-density requirements.
The structured cabling designed for the data center consisted of one combined copper MDA/HDA for network connectivity and another for fiber connectivity for the SAN. This centralized approach for the structured cabling design was used due to the relatively small size of the data center and the requirement to maximize the raised floor space for end-user equipment such as servers and storage. Also, separating the fiber and copper HDAs enabled the cable routes to be planned in way that would minimize congestion within the cable tray supporting the fiber and copper cabling.
Because the equipment layout within the data center located the servers to one side of the HDA, with the storage equipment on the other side, the majority of the cabling ran in one direction. While this was not ideal, it was necessary due to the client’s requirements regarding equipment locations and cabling diversity, and to properly manage power and cooling.
Working with the MEP engineers and the client, a multi-tiered cable tray was designed to support the high-density of cabling that was required to provide connectivity to the equipment. The two tiers of cable tray each separately supported designated rows of equipment. In this way, the cable fill within the cable tray was managed in such a way as to reduce cable congestion in potential choke points such as the HDA termination racks. This structured design allowed us to provide the client with a data center that afforded the flexibility required while maintaining all initial design constraints.