Planning entry routes
From the outset, the way that the Telcos and carriers will bring their fibres into the facility should be considered. This will largely be dictated by the external geography and terrain, but the route will generally be along a main road or its pavement, then by the shortest route to the building basement or ground floor void. It is particularly important to consider how to achieve at least two diverse routes, where fibre cables can come from opposite directions without sharing common ducting. Many customers require such diverse routings to achieve their resilience targets (see figure 1, left).
One thing's for certain, each time a new carrier needs to bring fibre into a facility it's likely that there's digging to be done. With a little forethought and planning, this can be minimised.
Future changes can be simplified if ducting is pre-installed across the property to a footway box or roadside cabinet. This can be installed just inside the property without the need to obtain way leaves, although in some cases it may be preferable to obtain the necessary way leave and local authority consent to install it in the pavement. Footway boxes tend to be more anonymous than roadside cabinets and are therefore less prone to damage and vandalism.
Having installed a footway box or roadside cabinet and an ample amount of ducting, when each new carrier needs to bring fibre into the facility their dig stops at this point. The fibre cable can then be pulled through the ducts to the inside of the building and terminated on a suitable cable management and splicing system.
In most cases providing such ducting is sufficient, but some collocation owners may wish to install fibre right down to the footpath boxes. Sufficient amounts of suitable, external-grade fibre would be needed in the footway box for this purpose, together with underground splicing enclosures. A further option would be to provide partially populated, blown-fibre cables to the footway box, since this allows new fibres to be easily blown in at a later date.
Whichever option is chosen, it should be ensured that plenty of capacity is installed at day one or there'll still be the nightmares of a dig at some future date, with the potential for damage and disruption to existing services.
Basic calculations can be used to give an indication of the maximum capacity needed to provide to the building, based on the number of potential customers and their theoretical maximum usage. These are similar calculations to lighting, cooling and power estimates.
Getting inside
External grade fibre is much tougher than internal grade and has extra strength members, making it more difficult to handle.
Often this type of fibre is filled with petroleum jelly to stop moisture ingress. This is not only messy when terminating the cable, but represents a fire hazard when inside a building. For this reason many local authorities restrict the use of jelly-filled cables to only five metres into a building.
The use of a building entry transition point is strongly recommended. Usually this is a frame or cabinet with the necessary cable management for heavier external cables and all of the splicing arrangements needed to connect from external grade to internal grade fibres. Splicing, rather than patching, is used at this point to reduce attenuation and maintain the power budget. The internal grade fibre cables are then taken to an optical distribution frame (ODF) or, less ideally, direct to customers' cabinets.
Often located in the basement, the building entry frame or cabinet would generally have separate splice shelves allocated to individual carriers for segregation. For security purposes it needs to be either caged or in a lockable room.
Products such as Krone's Fibre Distribution Unit (FDU) can be used for this application. Such products achieve a high packing density and use swing-out splicing shelves to allow individual carriers to work on their fibres with no risk of disrupting others.
Occasionally, when the collocation hall is on the ground floor or basement, it can be possible to combine the functions of the building entry frame and ODF by fitting patching adapters to the front of the FDU splice shelves.
It is not essential to have an ODF – many collocation facilities run the incoming fibre cables straight to the cabinets in which they're needed. This is fine, provided that all the fibres are going to the same cabinet. The major drawback of this strategy is that its likely that the floor will have to be lifted on a regular basis, every time an addition, move or change is needed.
Although it is cheaper, initially, to not have an ODF, many collocation operators have now reached the same conclusion as office network managers: the flexibility and labour cost savings on every additional move or change very quickly pays for the initial cost and gives reduced overall life costs.
When using an ODF, an ample amount of fibre tie-cables are installed from the building entry frame to the ODF, where they are terminated ready for later use. When new fibre cables are brought into the building they only need to be spliced to the tie cables and are immediately available on the ODF for patching to wherever they're needed.
An alternative to pre-installing populated fibre tie-cables is to use part-populated, blown fibre tubes – reducing slightly the initial installation cost. Extra fibres can be blown in later.
Taking a structured approach
The logic and economic reasoning for taking a structured approach to fibre cabling a collocation facility is similar to that for office blocks: the disruption and cost of repeated adds, moves and changes. The telecoms industry realised this many years ago, hence the use of intermediate distribution frames (IDFs) in addition to main distribution frames (MDFs) in telephone exchanges.
Constant change is a factor that is virtually a certainty in any collocation facility. These changes can be caused by new customers, existing customers adding new cabinets, ISPs adding new carrier routes and changing bandwidth suppliers. There are even frequent 'temporary' requirements, where circuits need to be patched-in for a week or less. This is all highly disruptive, and expensive in terms of labour, if the floor has to come up each time.
A structured approach also avoids the potential for the spaghetti jungle that can grow beneath the false floor of many facilities as customers run their own cabling between cabinets and suites. Not only are such installations messy, but they are not controlled and often there is no physically tracing – no-one is sure which cable does what or even who it belongs to. If a structured system with a 'Meet-me room' is planned and provided, all of the fibre, untwisted pair (utp) and co-axial cable can be presented on patch frames in a well organised and documented fashion.
It is possible, and prudent, to pre-install fibre from the ODF to each potential cabinet position, so that as each new cabinet is installed a cable can simply be raised up from the floor void and terminated onto a fibre patch panel inside the cabinet.
The same can be done with co-axial and UTP for digital signals (see figure 2, left).
All that is needed to provide or cease circuits is for the correct patch cord to be inserted or moved. No floors to be lifted, no long lead-lines to schedule the work and, as it is all pre-tested during installation, no termination, testing and fault-finding time. This enables the provision of a faster, more flexible, service, particularly for the last-minute, short-term requirements.
Systems can be sourced now. Krone's TrueNet structured cabling system, Category 5e and 6 cable have warranted throughput, and, as other such products, give far better service to customers. Such systems will give a point of competitive advantage.
The Meet-me room
The Meet-me room is similar to a communications room. Every cabinet in the collocation space is cabled back to this room in a star topology. It may be necessary to run fibre and UTP copper to optical and RJ45 patching frames; plus co-axial cable if clients include Telcos. The convention is to provide three separate frames in the Meet-me room: ODF for optical fibre, DDF for co-axial and patch panels for Category 5e or 6 cabling (see figure 2, above left). Products, such as Krone’s AccessNET™ MMDF (multiple media distribution frame), can combine these onto a single frame, allowing for a high packing density that takes up less space. Diverse routing and no single point of failure are the mantras of most Telcos, carriers and ISPs. They require diversity of fibre routes from the building to their various networks. The simplest way to achieve this is to have fibre entry points and duplicated Meet-me rooms at diagonally opposite ends of the building (see figure 1, above left). Within a building, diverse routing of fibre and copper cables is also advised. Fibre should be tested with an optical time delay reflectometer to ensure that it is correctly installed and terminated. It is now possible to install fibre monitors using interfaces. These offer service level monitoring as a value-added service. Such monitors use a fibre tap to take a light sample (5% or less of the light in the fibre) that can be regularly tested for its power level to give early warning of signal degradation. They are also invaluable at a demarcation point for determining the direction in which a fault lies – identifying the fault ‘owner’ when rapid restoration needs to be resolved. Connectivity is as essential as power and air conditioning. Proper consideration at the outset, in conjunction with an experienced installer or manufacturer, will pay dividends in terms of lower operating costs, increased flexibility, faster response to customers’ needs, less physical disruption and lower risk of damage to operational cables.Task management
The objective of the test programme was to examine the short and long-term effects on Category 5e and 6 cables when subjected to pressure from the total weight of the cables installed in a wire tray containment system, together with any subsequent effects this might have. During the tests, 90 m lengths of Category 5e and 6 test cable were placed in a wire cable tray, subjected to zero load and tested to the requirements of TIA/EIA-568A Draft II (TSB-95) and TIA/EIA-568-B-2-1 Draft 5. A load was then applied to the cable. This was done by placing a number of heavy Lexan strips on the cables in succession. Calculations showed that five Lexan strips correspond to a total of 40 Category 5e cables resting on the test cable. This is approximately equivalent to a depth of 200 mm of cable laid in the tray. A second set of measurements was taken under these load conditions, which allowed the difference in performance before and after the loading to be calculated. To determine if any changes in performance were due directly to the effect of the containment method, the tests were repeated with the cable laid on a flat, even surface. By comparing these results, the effect of the containment could be seen in isolation. It was clear from the results that the load on the cables at the pressure points of the cross wire in the tests had no negative impact on the performance of the cable. The tests also revealed the effects of high temperature on the cable to be significant. Temperature cycling tests showed that a containment system that allows air to circulate freely has a positive advantage over an enclosed environment or flat base, in which heat is unable to dissipate and can lead to an unacceptable rise in temperature. Resulting benefits
Although the test data covers a limited number of cable types, it has been met with great interest and is generally regarded as reliable. The benefits of wire cable trays are well documented. Ensuring that cables are raised above floor level by a free-draining, ventilated and protected system will produce optimum performance. The maximum depth of cabling should be no greater than that recommended by the specific manufacturer. If the system is readily available, quick and economical to install, this is of obvious benefit to both the installer and the end-user. Cablofil believes that its example should be followed by other leading manufacturers, in the provision of supporting test data and documentation for similar systems. It is clear that any additional test data that can be supplied by cable manufacturers to indicate the effect on performance of a range of containment systems and environments would be welcomed by designers and installers alike. International standards are being formulated to include certain aspects of cable containment, but applications and products can vary between countries. Without hard evidence or substantiated facts there is a real danger that practical decisions, based solely on assumption or rumour, can be misleading and expensive.
Voice & data cabling products
Source
Electrical and Mechanical Contractor
Postscript
Mike Williams is collocation market development manager at global connectivity specialists Krone
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