[ntp:questions] GPS Weakness Could Sink Wireless

unruh unruh at invalid.ca
Thu Dec 12 20:00:59 UTC 2013

On 2013-12-12, Rob <nomail at example.com> wrote:
> Jan Ceuleers <jan.ceuleers at computer.org> wrote:
>> Interesting Light Reading article on the degree to which infrastructure
>> (in casu wireless networks) is dependent on GPS timing signals, how
>> little is needed to jam GPS (intentionally or otherwise), and what the
>> impact of such jamming would be.
>> It also talks about how PTP might or might not mitigate some of these
>> issues.
>> http://www.lightreading.com/mobile/mobile-security/were-jamming-gps-weakness-could-sink-wireless/d/d-id/706895
> It depends on the structure of the network and the required accuracy.
> Remember that the usual GPS jamming methods are quite local in nature.
> You can jam my GPS but that won't take out my DCF77 receiver or the
> three GPS-synced servers I have configured as internet NTP sources.

If they are in the same locality (or, depending on the strength of the
jamming, local could mean within a few Km) they could also be jammed. 
Also, transmitting time via a network (whetehr wired or radio) can have
a fair amount of jitter so it depends on the accuracy that the wireless
towers need. If it is seconds no problem. If it is nanoseconds, you just
won't get that.

> Nor will it take out my peer server that itself has DCF77 and some
> other internet time sources, that are again synced to different other
> servers.
> Of course it is possible to jam everything, just not very likely.

The article talks about a truck driving by the airport (ie a few km)
jamming the airport. And that was a trucker probably unwilling to spend
more than a 100 dollars on his jamming gear. 

> In a mobile network, it should be possible to get time information
> both from the local GPS receiver and via the glass/microwave link
> as a backup.

But does it have the required accuracy? I do not know. 

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