Proper cable management strengthens network reliability, improves performance and lowers operating costs.
By Kam Patel
As business, university and government network managers continue upgrading their networks to transport high-bandwidth broadband services, an increase in fiber usage is essential to meet both the bandwidth and cost requirements. But just deploying this additional fiber is not enough. A successful, well-built network also must be based on a strong fiber cable management system.
Proper fiber management has a direct impact on the network's reliability, performance and cost. Additionally, it affects maintenance, expansion and moves, adds or changes (MACs). The four primary elements of a strong fiber cable management system are bend radius protection, cable routing paths, cable accessibility and physical protection of the fiber network. Executing these concepts correctly will enable the network to realize its full potential.
With strong demand steadily increasing for broadband services that will include several bandwidth-hungry technologies like high-definition television (HDTV) and higher Internet speeds for handling larger file sharing requirements, fiber is being pushed closer and closer to the customer premises. This, in turn, creates a need for additional fiber in the data center and backbone while active equipment must be managed to accommodate future network growth.
Any new broadband network infrastructure must have the inherent capability to easily migrate to the next generation of technologies and services. As the amount of fiber across the network increases, the importance of properly managing the fiber cables becomes a more crucial issue.
The manner in which fiber cables are connected, terminated, routed, spliced, stored and handled will directly and substantially impact the network's performance and, more importantly, its cost of ownership. The four fundamental elements of fiber cable management-bend radius protection, cable routing paths, accessibility and physical protection-are reviewed, as well as new technologies and products that have been developed in the past few years to improve these elements.
Bend Radius Protection
Two types of bends in fiber-microbends and macrobends-can affect the fiber network's long-term reliability and performance.
The microbend is a small, microscopic bend that may be caused by the cabling process itself, mechanical stress due to water in the cable during repeated freeze and thaw cycles, packaging or installation. External forces are also a source of microbends. An external force deforms the cabled jacket surrounding the fiber but causes only a small bend in the fiber.
A microbend typically changes the path that propagating modes take, resulting in loss from increased attenuation as low-order modes become coupled with high-order modes that are naturally lossy. A macrobend is a larger cable bend that can be seen with the unaided eye and is often reversible. As the macrobend occurs, the radius can become too small and allow light to escape the core and enter the cladding. The result is insertion loss at best, and in worst cases, the signal is decreased or completely lost. Through proper fiber handling and routing, however, both microbends and macrobends can be reduced and even prevented.
The minimum bend radius will vary depending on the specific fiber cable. In general, the minimum bend radius of a fiber should not be less than 10 times its outer diameter. Thus, a 3 millimeter (mm) cable should not have any bends less than 30 mm in radius. Telcordia recommends a minimum 38 mm bend radius for 3 mm patch cords. If a tensile load is applied to a fiber cable, such as the weight of a cable in a long vertical run or a cable pulled tightly between two points, the minimum bend radius is increased due to the added stress.
The advent of bend insensitive fiber is an example of how tech-nology has addressed the bend radius issue. Whereas the minimum bend radius should not be less than 10 times the outer diameter of the fiber cable in typical fiber, bend insensitive fiber provides more leeway.
However, designers must understand that these new fibers do not diminish the need for solid fiber cable management. On the contrary, the increase in the sheer number of fibers being added to the system to accommodate broadband upgrades makes bend radius protection as important as ever.
As fibers are added on top of installed fibers, macrobends can be induced on the installed fibers if they are routed over an unprotected bend. A fiber that had been working fine for many years can suddenly have an increased level of attenuation, as well as a potentially shorter service life. Although bend insensitive fiber is an innovative breakthrough in addressing the issue of bend radius protection, it may be some time before any network owner replaces existing fibers with a bend insensitive variety of fiber. Meanwhile, the importance of bend radius protection is critical to avoid operational problems in the network.
Cable Routing Paths
The second element of fiber cable management is cable routing paths and is related to bend radius protection because improper routing of fibers by technicians is one of the major causes of bend radius violations. Wherever fiber is used, routing paths must be clearly defined and easy to follow-to the point where the technician has no other option than to route the cables properly. Leaving cable routing to the technician's imagination leads to a fiber network that is inconsistently routed and difficult to manage.
The quality of the cable routing paths, particularly within a fiber distribution frame system, can be the difference between congested chaos and neatly placed, easily accessible patch cords. It's often said that the best teacher in fiber routing techniques is the first technician to route it properly. Conversely, the worst teacher is the first to use improper techniques since subsequent technicians are likely to follow that lead.
Well-defined routing paths therefore reduce the proficiency training time required for technicians and increase the uniformity of the work done by ensuring and maintaining bend radius requirements at all points to improve overall network reliability. It is important to note that, again, the use of bend insensitive fiber does not diminish the need for clear cable routing paths. There are benefits that go beyond bend radius protection.
Defined routing paths make accessing individual fibers easier, quicker and safer, reducing the time required for reconfigurations. Fiber twists are reduced to make tracing a particular fiber for rerouting much easier. Even with new technologies, such as the use of light-emitting diodes (LEDs) at both ends of patch cords for easy identification, well-defined cable routing paths still greatly reduce the time required to route and reroute patch cords. All of this directly affects network operating costs and the time required to turn up or restore service.
Cable access is the third element to good fiber cable management and refers to the accessibility of the installed fibers. As the number of fibers increases dramatically in both the distribution frame and the active equipment, cable access becomes an increasingly important issue. In the past, an active equipment rack might have had about 50 fibers exiting, and managing those fibers was much less of an issue. But as that same rack is fitted for next generation broadband services, there may be many more fibers involved, making proper management and accessibility vitally important matters.
With huge amounts of data and critical business systems moving across those fibers, the ability for technicians to have quick and easy access is critical. The last thing any business wants is service interruptions caused by mishandling one fiber to gain access to another. As previously mentioned, patch cords designed with LEDs at both ends can help technicians identify particular cable runs with no chance of error. These innovations can be implemented into a good cable management system to help minimize problems caused by disconnecting the wrong patch cord. There are many other tools and techniques for ensuring that every fiber can be installed or removed without bending or disturbing an adjacent fiber.
The accessibility of the fibers in the fiber cable management system can mean the difference between a network reconfiguration time of 20 minutes per fiber and one of more than 90 minutes per fiber. Since accessibility is most critical during network reconfiguration operations, proper cable access directly impacts operational costs and network reliability.
Physical Fiber Protection
The last element of a fiber cable management system addresses the physical protection of the installed fibers. Every fiber throughout the network must be protected against accidental damage by technicians or equipment. Fibers traversing from one piece of equipment to another must be routed with physical protection in mind, such as using raceway systems that protect from outside disturbances. Without proper physical protection, fibers are susceptible to damage that can critically affect network reliability. The fiber cable management system should always include ensuring that every fiber is protected from physical damage.
A Final Word-Planning
Because many businesses are upgrading their networks for delivering high-bandwidth broad-band services, it is important to stress the need for planning in terms of cable management. Today's network is a living and growing entity.
What is enough today will almost certainly be too little for tomorrow. Future-proofing the network wherever possible should be a major consideration, and fiber cable management is no different. Is the raceway system designed for growth in fiber count without sacrificing accessibility? Is the fiber distribution frame sized to accommodate growth in a centralized location without sacrificing protection of fiber jumpers? It is far less expensive to plan and build for growth today than a costly, time-consuming, service-affecting retrofit.
Ignoring future growth, particularly in terms of fiber, will result in higher long-term operational costs because of poor network performance or a requirement to retrofit products that can no longer accommodate network demand.
Another consideration in planning for good fiber cable management concerns the active equipment rack. Most manufacturers have traditionally overlooked the need for providing cable management within their equipment. Before purchasing, network planners should insist that cable management is included within every piece of active equipment to ensure it will operate efficiently over time.
Cable management should address all four elements of fiber cable management-bend radius protection, cable routing paths, cable access and physical protection-to strengthen the network's reliability and functionality while lowering costs and ensuring smooth upgrades when necessary.
Reprinted with permission of BICSI News. www.bicsi.org