How to Specify Rapid Fibre Deployment Optical Cabling B Elliott There are many advantages to using pre-terminated optical cable and even more can be realised when using Rapid Fibre Deployment (RFD) optical cable featuring the latest MTP optical array connector. Rapid Fibre Deployment (RFD) optical cabling is factory terminated with an MTP optical connector fitted at both ends. These miniature connectors terminate 12, 24 or even up to 72 optical fibres. The MTP connectors have a simple push-fit arrangement to allow them to be simply fitted into the back of specially modified optical patch panels. The user of the cabling system still sees industry standard LC or SC connectors at the font of a normal rack-mounted patch panel. The advantages of the RFD optical cabling system are: - Greatly reduced time on site: Users can expect time on site to be reduced by about 95% compared to traditional direct termination of fibre techniques. A 48-fibre link can be installed in about twelve minutes compared to the four and a half hours traditional termination would take for the same amount of fibre. - Increased operating efficiency: Reduced cable size compared to conventional fibres, means improved air flow and therefore an increase in energy efficiency – lower cooling costs. - Better quality: Factory termination gives a much higher quality and lower optical attenuation than onsite techniques. 100% factory testing and on-site sample testing gives higher network reliability. - Less space taken up: The technique used in RFD termination allows an even smaller optical cable to be used compared to normal optical LAN cables. In the rack the RFD patch panel gives twice the cable density of the average optical panel; typically 48 fibres in a 1U (44 mm) slot. To specify an RFD optical system we need to: Decide on optical fibre type required. Decide on the number of fibres required in the link. Decide on the cable length. Decide on the number of connectors in the patch panel and their type. Picking the right kind of optical fibre To get the most cost effective solution for a communications project, the correct optical fibre has to be selected that reflects the distance and speed requirements of the Local Area Network (LAN). The standards-based naming method identifies three multimode fibres, known as OM1, OM2 and OM3 and two single mode fibres, known as OS1 and OS2. It then comes down to a case of selecting the correct fibre according to the speed and distance expectations from the following chart. Distance Speed 300m 500m 2000m 10Mb/s OM1 OM1 OM1 100Mb/s OM1 OM1 OM1 1Gb/s OM1 OM2 OS1 10Gb/s OM3 OS1 OS1 Table 1 The horizontal axis is the distance limitation, e.g. up to 300 metres, 500 metres and 2000 metres. These links would then be known as OF300, OF500 or OF2000. The vertical axis gives the speed in megabits per second, and the scale goes from 10 Mb/s to 10 Gb/s. One then selects the appropriate fibre according to the requirements. For example if we need to transmit ten gigabit Ethernet up to 300 metres then an OM3 fibre is required. Fibre Types The multimode fibres are usually expressed in terms of core size relative to cladding size, e.g. 50/125 or 62.5/125. The first number denotes the core size in microns and the second number gives the overall cladding diameter. Singlemode would be called 9/125 in this terminology. According to the Standards (ISO 11801:2002) OM1 and OM2 can be either 50/125 or 62.5/125, but the market seems to have decided that OM1 always means 62.5/125 and OM2 always means 50/125. OM3 is always 50/125 as only that smaller core size could offer the extra bandwidth required. OM3 is a very high quality fibre offering exceptionally high bandwidth. It is recommended that OM3-based pre-terminated assemblies do not go beyond 300 metres and other pre-terminated assemblies go beyond 500 metres. For Local Area Networks Connectix recommends OM3 fibre as it gives ten gigabit Ethernet performance for at least 300 metres. Deciding upon the number of fibres in a link It generally takes two optical fibres to make a link; one for the transmit leg and one for the receive. For links between cabinets or floors it would not be cost effective to install less than eight fibres and twelve fibres is the most common. Twelve fibres of OM3 fibre would provide six ten-gigabit links. That’s equivalent to about ten thousand compressed video channels! Connectix recommends standardising on 12-fibre MTP links to give adequate future network capability. Deciding on the cable length It is important to get the length right when ordering pre-terminated cabling assemblies. Links that are too short will have an obvious problem. Cable links that are too long present excessive cabling that has to be stored somewhere within the cabling containment. If measuring off a floor layout diagram remember that the cable will not always follow the shortest route from A to B and an extra four metres should be allowed for termination in two racks, e.g. if the shortest route between two racks is x then the cable distance is more likely to be 1.1x + 4 metres. When going between floors an allowance of four metres per floor should be given. Connectix recommends letting the cable manufacturer survey the routes and take responsibility for correct lengths. Decide on the size and type of patch panel The cables will terminate in standard 19 inch rack mounted patch panels. Each 1U patch panel can terminate up to 96 fibres. The options are: A ‘standard’ panel where the front face of the panel contains spaces for up to 48 duplex optical connectors. A modular panel where up to four cassettes fit into a 1U frame. Each cassette presents up to twelve duplex optical connectors on the front and one or two MTP connectors on the back. The ‘XS’ panel, as the standard panel, but with an excess cable store built onto the back of the panel. The connectors in the panel can be: Multimode or singlemode LC or SC The fibre type within the panel that links the MTP connector at the back to the LC or SC connector at the front must be exactly the same type as that used in the rest of the cable link, e.g. OM1, OM2, OM3, OS1 or OS2. A link specification might therefore look like: Fibre type: Number of fibres: Link length: Cable type: Patch panels: Patch panel specification: OM3 12 250 m Indoor grade low flammability 2 1U, 19 inch rack mounted Modular cassette system 1 cassette preloaded with 6 x OM3 multimode LC duplex adaptors 3 blanks (for future expansion) This would be everything you need for 6 250 m 10 gigabit Ethernet links. Connectix recommends the LC connector for Local Area Network optical links. Other options Cable types All of the Connectix Starlight MTP-based rapid fibre deployment optical cables feature low flammability cable sheaths for indoor use. As an option a larger ruggedised cable is available for areas where the cable may be exposed to more mechanical stress. Labelling It is essential that all patch panels in any cabling system are fully labelled so they can be identified. Connectix Starlight panels can be ordered pre-labelled with any scheme required for any kind of installation. Higher performance for singlemode fibre Singlemode fibre offers exceptionally high bandwidth and low loss. Most of the loss in a short singlemode fibre link will come from the connectors. As a standard, Connectix Starlight features 0.25 dB typical, 0.75 dB maximum insertion loss and 80 angle polish with 55 dB Return Loss. The angle polish is important in single mode systems as it prevents powerful laser light being reflected back into the laser by the first connector. If this is not enough then there is the Premium Starlight option featuring 0.1 dB average and 0.35 maximum insertion loss MTP connector. Specifying the MTP array connector It is important that the MTP connector meets all the international standards and specifications required for an array connector to guarantee system performance and intermatability with other components. The specification is: Meets IEC Standard 61754-7 Meets TIA/EIA 604-5 Type MPO Meets ANSI HIPPI 6400 Standard Optical Internetworking Forum (OIF) Compliant Infiniband Compliant 10 GFC Fibre Channel Compliant Insertion Loss Optical Return Loss Operational Temperature Durability Premium Starlight Singlemode Ferrule Standard Starlight Singlemode Ferrule Standard Starlight Multimode Ferrule 0.10dB Typical (All Fibres) 0.35dB Maximum (Single Fibre) 0.25dB Typical (All Fibres) 0.75dB Maximum (Single Fibre) 0.20dB Typical (All Fibres) 0.50dB Maximum (Single Fibre) > 55dB (8° Angle Polish) > 55dB (8° Angle Polish) > 20dB -40° C to +80° C -40° C to +80° C -40° C to +80° C < 0.3dB change after 500 remates (per EIA-45521A) < 0.3dB change after 500 remates (per EIA-45521A) < 0.2dB change after 500 remates (per EIA-455-21A)