IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Communications Remarks
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S 5.60 Selection of a suitable backbone technology
Initiation responsibility: Head of IT Section, IT Security Management
Implementation responsibility: Head of IT Section, Administrator
The selection of a network protocol for the backbone is a decisive factor for
the security and availability of the local network because the protocol has
major influence on the available bandwidth and performance. If the cabling is
planned without commitment to special services (e.g. proprietary solutions)
(see also T 2.45 conceptual weaknesses in the network), a change in backbone
technology is principally feasible. Even though this requires a considerable
organisational, personnel and financial effort.
A general recommendation with regards to IT security for a specific backbone
technology cannot be given because many individual aspects have to be taken
into account. The advantages and disadvantages of the most common network
protocols are given in the following:
There are four base technologies Ethernet, Token-Ring, FDDI, and ATM
which can be described as follows:
Ethernet
Ethernet technology is defined in the IEEE 802.3 standard and based on the
CSMA/CD (Carrier Sense Multiple Access / Collision Detection) technique.
With this technique, all stations are equally entitled to access the transmission
medium, although it can only be used by one station at a time. When a station
needs to transmit data, it first checks if the transmission medium is available
for use (carrier sense). If it is, the station starts data transfer. If several stations
start transmitting data simultaneously (multiple access), a collision occurs and
is detected by the affected stations (collision detection), whereupon the
medium is checked again and a renewed attempt is made at transmission.
As CSMA/CD is a stochastic technique, it does not guarantee the availability
of any dedicated bandwidths. For this reason, it is not very suitable for
multimedia applications which require a fixed bandwidth, for example.
Consequently, Ethernet-based networks do not ensure any particular Quality
of Service (QoS) in general. Gigabit Ethernet systems have a technique
similar to QoS.
There are three types of Ethernet which basically differ from each other only
in terms of the supported transmission rates:
- Standard Ethernet
Standard Ethernet, a predecessor to the other two variants, has been in use
for a long time. It provides a transmission rate of 10 Mbit/s, it is an
unsuitable backbone technology for most local networks, as a rise in the
network load is accompanied by a sharp increase in the number of
collisions, causing the throughput to drop steadily.
- Fast Ethernet
Due to the rising number of networked computers and the resulting
increase in network loads, Standard Ethernet urgently needed to be
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IT-Baseline Protection Manual: Oktober 2000