There are many considerations regarding the outside plant portion of any fiber-to-the-premise (FTTP) net- work architecture. Each area must weigh in on issues of cost, flexibility, performance, accessibility and other important criteria. As fiber gains momentum for use in delivering high-speed broadband services to homes and small businesses, questions have surfaced regarding the best way to connect the large numbers of drop cables feeding into the network. Typically, drop cables connect each optical network terminal at the subscriber premises to a fiber access terminal, where they are then connected to a main fiber distribution frame for routing to the central office. The fiber plant can be either aerial (above- ground) or buried (belowground). With an aerial plant, the service terminal is usually mounted on a stand or pole and technicians have easy access for service and maintenance issues. In a buried plant, however, the drop cable will be buried below the frost line, yet requires the same ease of accessibility for technicians. The two most common methods for creating access points while connecting buried drop cables are above the ground (pedestal access) and below the ground (hand hole). But there are important considerations attached to each method, such as splicing vs.connectors, ease of accessibility, environmental issues and the effects of severe temperature variation. Splicing vs. Connectors The decision to splice or use connectors in the outside plant has been discussed at length — and the pros and cons of both methods are numerous. The basic train of thought is that a connector pair is more beneficial at any location where technicians may require access on a regular basis, such as for testing, service turn-up and reconfiguring the network.At these locations, a connec- tor interface provides significant operational cost and time savings over fusion splicing. The fiber access terminal requires the advantages con- nectors provide.There are new hardened connectors avail- able for use in the outside plant that can withstand the harsher environmental conditions.With new technologies in hardened connectors, it simply makes sense to take advantage of the benefits they bring to the outside plant. Hand Hole vs. Pedestal Access A hand hole is basically a hole built into the ground that enables the technician to simply open it up and work on the network. Hand holes are placed at any location that would require access for maintenance, connecting addi- tional drop cables or troubleshooting. However, the use of an aboveground pedestal provides even easier access for the technician. With pedestals, the distribution cable and drop cables are still underground. Both are brought up through the bottom of the pedestal, and connections are made inside the unit. The obvious 34 LastMILE May|June 2007 lastmileonline.com Fiber Drop Cable Connections — Above or Below Ground? Fiber Drop Cable Connections — Above or Below Ground? Different Circumstances Dictate Use of Aboveground or Belowground Connectivity By Ray Hagen advantage is being able to access the terminal much easier than working through a hand hole. Another advantage of using pedestals is cost.From a con- struction standpoint, a typical pedestal is less expensive to install when compared to the placement of a hand hole. Installing a hand hole requires a large digging operation, whereas a pedestal only takes a much smaller hole for mounting — thus lowering network construction costs significantly.The test access offered by the pedestal allows superior access for troubleshooting or working on a connection during the operation of the network. One disadvantage of using pedestals is their location in open areas where they are susceptible to vehicle damage. Untrained technicians can also gain easy access, as well as any curious person who may want to break in or vandalize the pedestal or equipment. Probably the big- ger disadvantage of using pedestals is pure aesthetics. Neighborhoods may frown on having pedestals installed every two to four houses and prefer that everything remains under the ground. Environmental Issues In cases where pedestals may not be aesthetically appealing or there is concern about possible damage from vehicles or vandals, it may make better sense to deploy terminals below the ground — or use a hand hole. Inside the hand hole, another splice closure provides additional environmental protection. The splice closure connects the drop cables within the hand hole and, therefore, must be substantially more robust in design as compared to the aboveground pedestal. The placement of hand holes below the ground line presents more opportunity for a flooded environment,so the ability to withstand submersion under fairly significant water is important. It must also withstand the possibility of freezing and thawing in northern climates.Today, there are very good splice closures available on the market that can hold up very well under very harsh environmental conditions. It’s also worth noting that choosing to use hand holes in very harsh winter environments makes them subject to being iced over or frozen shut. It creates the possibility that responding technicians may spend considerable time and effort just finding a way to chip or melt the ice away to gain access. Once open, the technician will likely find additional ice and slush that must be cleared away before doing any work.The point is that hand holes used under extreme weather conditions can make maintenance particularly difficult during the winter months. Effects of Temperature Severe temperature changes can have detrimental effects on outside plant cable assemblies used in either a pedestal or hand hole environment.This has been an ongoing challenge for manufacturers in developing assemblies that are hardened against the effects of temperature. Basically, components used to construct outside plant cable assemblies are typically made of plastic and tend to shrink in cold temperatures. The exposure of fiber cable and cable assemblies to low temperatures is probably the single most common cause of signal transmission problems and failures in outside plant architectures. Insertion loss failures, for example, are the direct result of cable and assembly component shrinkage due to cold temperatures. If this shrinkage isn’t addressed in some way during the manufacturing process and deploy- ment planning, the optical fibers and components could eventually fail. As temperatures decrease to 40 degrees below zero, the effect on cable assemblies becomes significant as shrinkage occurs.The optical fiber in the cable, however, remains at its original length.This can cause the optical fiber to bunch up inside the temporarily shortened assembly.The result is that fiber can be severely stressed, causing micro-bends and high insertion loss at 1550 nm. In some cases, a fiber break could even occur. Since everything is below ground with a cover acting as an insulator for the fiber cable, drops, and interfaces, the hand hole access method provides some inherent protection against cold temperatures. In a pedestal envi- ronment, however, temperature changes are much more apparent.The temperature inside the pedestal will likely be as cold as outside temperatures in the winter, and probably warmer in the summer, since the enclosure itself heats up if exposed to direct sunlight. Therefore, it’s important for network architects to con- sider temperature challenges at each network location and their possible effects on drop cable connections. Whether they choose hand holes or pedestals for drop cable connections, these are critical points of the FTTP network and must be protected against potentially harmful environmental characteristics. The industry has made huge advances in access equipment and connector components that meet or exceed specifications for dealing with every environ- mental situation faced by FTTP networks, particularly in the outside plant.A little planning goes a long way in ensuring optimum performance, accessibility, and flexibility for driving the benefits of fiber directly to consumers. Ray Hagen is product manager for FTTX OSP hardened products in fiber cable management in the Global Connectivity Solutions Group at ADC (www.adc.com), headquartered in Eden Prairie, Minn. May|June 2007 LastMILE 35lastmileonline.com The most common methods for creating access points while connecting buried drop cables are belowground hand holes (left) and aboveground pedestal access. . — Above or Below Ground? Fiber Drop Cable Connections — Above or Below Ground? Different Circumstances Dictate Use of Aboveground or Belowground Connectivity. lowering network construction costs significantly.The test access offered by the pedestal allows superior access for troubleshooting or working on a connection