IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Communications Remarks
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Around the whole of this is another sheath to provide protection against
mechanical and optical influences. Optical fibres are available in two versions:
multimode and single-mode optical fibres. These two types differ primarily in
terms of the possible bandwidth and the maximum length that can be attained
without additional repeaters.
Optical fibre cables are generally used for bridging long distances (for
example connections between buildings or floors) in a backbone, and in some
cases in dual ring systems.
Advantages:
- The bandwidth and the unamplified range is greater than with copper cable.
- Tapping can be achieved only with substantial technical effort.
- Inadmissible rewiring/changes of line assignment can be easily identified
by means of the available technology.
- Optical fibre cables are insensitive to all non-destructive ambient
conditions, in particular to electromagnetic fields.
- Optical fibre cables require relatively little space.
- There is no cross-talk or interference between various optical fibres or an
optical fibre and TP cables.
- With optical fibres the fire load is lower in comparison with copper cables,
because they have less or different sheathing and also because as a rule less
cable material is required over a given route.
Disadvantages:
- The installation costs for optical fibre cables are very much higher than for
copper cables, mainly due to the splicing work required.
- The coupling components for the operation of optical fibres, especially for
single-mode optical fibres, are more expensive than those for copper
cables.
- Laying and preparing optical fibre cables requires special knowledge,
special tools and special additional components (e.g. splice boxes).
- Optical fibres cannot be bent through just any radius, as required. This may
make installation more difficult, as a result of the need to take account of
possible and necessary cable routing options.
An overview of the length restrictions on cables for some of the common
protocols (Ethernet, Fast Ethernet, FDDI and CDDI; cf. S 5.60 Selection of a
suitable backbone technology) is given in the table below:
Network access
protocol
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IT-Baseline Protection Manual: Oktober 2000
Cable type Max.
length
Ethernet 10Base2 Coaxial 185 m
10Base5 Coaxial 500 m