[ntp:questions] UK report on GPS vulnerabilities seems to overlook NTP

JohnAllen johnbenallen at gmail.com
Tue Mar 8 16:25:31 UTC 2011

Maybe I read this too quickly, but the report published today by the
UK Royal Academy of Engineering (see
and also the BBC coverage at http://www.bbc.co.uk/news/science-environment-12668230)
seems to be saying that many organisations are vulnerable to GPS
failures because their IT systems rely on GPS for precise time.

Can this be true? I would have thought that most systems are using
NTP, and synchronising with diverse enough time sources that
unavailable or incorrect GPS time would not cause short-term problems.

The relevant part of the report is on pages 13-14, where it says:

"GNSS timing is important for telecommunications applications.
technologies are much more efficient than asynchronous technologies
but require a
time source with appropriate accuracy, stability and reliability to
operate effectively
or at all, and GNSS can provide this. While ground-based clocks are
accurate enough
for this purpose (especially with the availability of chip scale
atomic clocks (CSAC)),
the synchronisation of many such clocks is problematic. GPS allows the
derivation of
synchronised UTC through resolving the signals from a number of
satellites at a
known position. Only a ‘good guess’ of the current time is required
and quartz clocks
have therefore been adequate for this process making synchronous time
significantly more cost effective.

The use of time can be split into three clear and separate aspects:
control, time of day and common epoch (usually UTC) time slot
alignment (also
known as ‘Phase’).
Stability of radio communications transmission, constant digital traic
low, time
slot alignment and traditional services over next generation Ethernet
infrastructure are some of the features that good time and timing
bring to
communications networks.
Financial systems increasingly need precise time stamping to
prioritise trades and
to provide an audit trail."

NTP is not mentioned anywhere in the report.

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