IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Communications Remarks
____________________________________________________________________ .........................................
S 5.3 Selection of cable types suited in terms of
communication technology
Initiation responsibility: Head of IT Section
Implementation responsibility: Network planner; Head of Site/Bldg
Technical Service
From the communications technology standpoint, the choice of cable is
determined by, among other things, the required data transfer rate (bandwidth)
and the distances to be covered without repeaters. The requirements arising
from the structural conditions at the installation location also have to be taken
into account when making the selection. In the following, the respective
advantages and disadvantages are described from an IT security point of view.
At present there can be considered to be two types of transmission media for
cable (as opposed to wireless) communications: copper cable or an optical
medium (optical fibre (FO)). Both of these types of media can be further
divided into various subcategories. The most important of these for the
medium of copper are the coaxial cable (one centre conductor with overall
screening) and the multi-core copper cable with the wires twisted in pairs
(twisted-pair cable, TP cable). These are explained in more detail below.
Twisted-pair cable
Twisted-pair cables are available in many different forms. These differ on the
one hand according to the nature of their shielding and on the other according
to their potential bandwidth. The current shielding classes are as follows:
- unshielded (UTP)
- unshielded but with overall screening (screened-unshielded, S/UTP),
- shielded, where the individual pairs of wires are shielded (shielded, STP)
- shielded TP cable with additional overall screening (screened-shielded,
S/STP).
In addition to their shielding designations, TP cables are divided into
categories according to their bandwidth and other electrical properties,
currently categories 1 to 5. A draft standard has been drawn up for categories
6 and 7. The rule here is: the higher the category, the higher the possible
bandwidth. The bandwidth is determined by various physical properties of the
cable. The commonly used UTP or STP cables in categories 3 to 5 can be used
to transfer between 10 and 100 Mbit/s over a maximum length of 100 m with
Ethernet or Fast Ethernet, while up to 155 Mbit/s can be transferred on
category 5 cables with ATM. Cables in category 6 will have a bandwidth of
600 MHz and therefore allow data transfer rates of up to 1 Gbit/s.
TP cables are at present mainly used for star-type cabling and in some cases
also for ring-type cable configurations.
Advantages:
- TP cables, and in particular the methods of preparing them for installation,
are relatively cheap in comparison with optical fibres if bandwidth needs
are low.
____________________________________________________________________ .........................................
IT-Baseline Protection Manual: Oktober 2000