IT Baseline Protection Manual - The Information Warfare Site

Threats Catalogue Deliberate Acts Remarks
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T 5.35 Overload through fax transmissions
Overloading by incoming fax messages can occur if there are not enough fax
lines or telecommunications lines or channels. Furthermore, a fax connection
can be intentionally blocked if
- long faxes are sent continuously (possibly containing information which is
of no interest to the recipient);
- sending of faxes is deliberately continued until the fax machine runs out of
paper and the buffer memory is exhausted.
A fax server can also become overloaded if faxes continue to be sent to it until
the storage space available on the hard disk is exhausted. However, it should
be borne in mind that a single faxed A4 page occupies approx. 70 KB. Given
the size of hard disks today, this means that a huge volume of incoming faxes
is needed to exhaust capacity. Moreover it should be borne in mind that there
is only a limited number of lines or channels available and every fax
transmission also requires time to process the fax protocol. Overloading of the
fax server in this way is only possible if the hard disk selected has too little
capacity or the fax server is also used to archive faxes.
Unlike conventional fax machines, it is entirely possible for a fax server to be
overloaded due to outgoing fax transmissions. Thus a fax server's processing
capacity could become completely exhausted by a very large number of serial
fax transmissions, which would then mean it was no longer available to
receive incoming faxes.
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IT-Baseline Protection Manual: Oktober 2000
Overload due to
incoming fax
transmissions
Overload due to
outgoing fax
transmissions