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

unruh unruh at wormhole.physics.ubc.ca
Tue Mar 8 18:39:17 UTC 2011


On 2011-03-08, jimp at specsol.spam.sux.com <jimp at specsol.spam.sux.com> wrote:
> JohnAllen <johnbenallen at gmail.com> wrote:
>> Maybe I read this too quickly, but the report published today by the
>> UK Royal Academy of Engineering (see
>> http://www.raeng.org.uk/news/publications/list/reports/RAoE_Global_Navigation_Systems_Report.pdf
>> 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.
>> Synchronous
>> 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
>> keeping
>> significantly more cost effective.
>> 
>> The use of time can be split into three clear and separate aspects:
>> frequency
>> 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
>> based
>> 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.
>
> Nor would I expect it to be.
>
> There is a big difference between keeping a computer's time of day clock
> set to the current time (NTP) and maintaining timing or frequency control
> in a telecom system.

And exactly what is that difference? While ntp is perhaps too slow to
respond to local frequency changes, how do you see the difference
between keeping a computer's idea of local time accurate from keeping a
telecom's idea of local time accurate?
>
>
>




More information about the questions mailing list