Question & Answer
Question
Optical Cabling Best Practices
Cause
Optical Cabling Best Practices
Answer
With fiber cabling used in the data center today, information transfer occurs in two directions simultaneously. This method uses 2 optical fibers contained in a single fiber optic cable and physically connects to ports at each end which houses the transmitter and receiver in a single assembly. The fiber element within an optical cable usually consists of a glass core and a cladding. The glass core provides the light path, the cladding surrounds the core to protect it, and the optical properties of the core and cladding junction cause the light to remain within the core. Although the core and the cladding diameters, expressed in micrometers, or microns, are often used to describe an optical cable, they actually indicate the physical size of the fiber element.
Mishandling a fiber optic cable will lead to microscopic internal faults within the glass core. In some cases this can cause a complete failure of a cable. Often, faults result in intermittent problems that require a specific cable orientation. This type of fault can be difficult to isolate There are a number of precautions that should be taken when handling fiber optic cables.
- Make sure the cable cutouts in the floor tiles have the appropriate protective edging.
- Route the cables away from any sharp edges or projections that could cut the outer jacket.
- Do not route the cables near unprotected steam or refrigeration lines.
- Do not coil or bend the cable in a very tight coil.
- Do not pull cables into position; place them.
- Do not grasp the cable with pliers.
- Do not attach a pull rope or wire to the connectors.
- Always clean the connectors before attaching them.
- Do not remove the protective plugs or protective covers until you are ready to clean the connectors and attach the cables to a device.
- Always leave the protective plugs and protective covers on unused ports and cable connectors.
- Connect the cable carefully to prevent damage to the connector housing or the fiber optic ferrules.
- Before inserting the connector, make sure the connector and receptacle keying are aligned.
- Do not mix different cable sizes (primarily 62.5 and 50 micron) cables in the same port-to-port link.
- Use cables of the correct length so that coiling excess cable is not necessary.
- Use cable management guides for vertical and horizontal support as well as to prevent bend radius violations.
- Avoid using any cable with damaged connectors.
- Avoid using any cable which has kinks and/or torn outer cladding.
A common issue with cable management is cables overlapping multiple pieces of equipment. This simple design flaw has two major effects on infrastructure. A single component may be hindered or prevented from being replaced without added interruption. A typical environment implements a SAN design that has both resilient and redundant components. In order to benefit from this architecture, it is critical that a component can be replaced without interruption to the SAN. Due to overlapping cables, adjacent devices may need to be disconnected to remove or replace a component. This can turn a simple procedure that would only slight reduce the integrity into a massive disruption.
The second major impact on the SAN infrastructure occurs when overlapping or bundles of cables impede the exhaust of a device. This condition needs careful monitoring to ensure cable integrity is not reduced from exhaust heat or the device has poor air circulation which results in the device overheating.
When installing fiber cabling, use labels on each end of the cable which provides sufficient information to identify the appropriate connection ports. Use a logical naming scheme to uniquely identify every cable along with its source and destination points. Good labeling reduces potential confusion as well as easing the task of finding a specific cable in a bundle. Cable labels should always be included as a key step for routine change management documentation and standard operating procedures.
Plastic zip ties should not be used with optical fiber cabling. If pulled too tightly, the zip tie will damage the cable’s core and/or outer cladding. Velcro tie wraps are strongly suggested. Try to not bundle a large number of cables together in a single group. Instead, bundle a few cables together and then combine these smaller bundles into larger groups. This practice provides for proper support of cables yet allows for easy isolation and/or replacement of a bad cable with minimal impact. Bundle ties should be located every 2 feet, or less, of cable run.
Depending on the maker of the fiber cabling, the proposed minimum diameter for bending a fiber optic cable can vary significantly. Some vendors provide a simple measurement, while other vendors state that bend diameters should not be less than some number of cable thickness. In the absence of a ruler in the data center, a simple guideline is to use the width of four fingers of two hands. If the diameter of a cable bend is less than that measure, then the bend radius is likely too tight.
Good cable management involves planning within every rack, between racks, at patch panels, in the data center and beyond. Good cable management implies a structured and consistent approach when planning and then implementing cabling. This key concept applies to both optical and wired media since both are likely to be co-located in the same space. Good cable management will address concerns for the current needs while having the flexibility to meet future needs due to technology changes, increased port counts, increase port density or some custom requirement.
A good source of information about planning cable infrastructures can be found in the Telecommunications Industry Association standard TIA-942 titled “Telecommunications Infrastructure Standards for Data Centers”. Beside cabling infrastructure, this standard also covers topics such as site space and layout, tiered reliability and environmental considerations.
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Modified date:
19 August 2022
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