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:
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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:
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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:
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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:
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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)