[Starlink] Time Synchronization in Satellite Networks

[Sebastian Moeller]

Hi Hesham,


> On 2. Apr 2024, at 00:04, Hesham ElBakoury <helbakoury at gmail.com> wrote:
> 
> Hi Christian,
> The problems is that Satellites move, therefore,  the delay between the different directions is different which violates the condition to run NTP and PTP. 

But GPS Satellites themselves are not in geostationary oprbit, and still we can get precision time from them... so I would argue that must be a solved problem, no?

Regards
	Sebastian

> 
> Hesham
> 
> On Sat, Mar 2, 2024, 8:19 AM Christian von der Ropp <cvdr at vdr.net> wrote:
> Hi Hesham,
> 
> You do not acquire the time from a LEO satellite but directly from the GPS satellites which carry an atomic clock on board.
> I'd not be aware of any LEO providing a GNSS signal but Xona plan such system (although not carrying proper atomic clocks but probably chip-sized atomic clocks that require frequent syncing with proper atomic clocks):
> https://twitter.com/Megaconstellati/status/1708091536439673323
> 
> There are efforts to build trapped-ion quantum clocks that are expected to become significantly smaller and cheaper than traditional atomic clocks while as accurate which would make it viable to put an atomic clock-equivalent on small LEO satellites. Once that happens you would have an independent alternative to the big GNSS birds in MEO but with stronger signals. I'm told that we are 5-10 years away from such trapped-ion quantum clocks.
> 
> But for NTP clients, the described method (running a local NTP server in the satellite terminal synced to GPS) should be good enough.
> 
> Christian
> 
> 
> Am 2. März 2024 18:02:47 OEZ schrieb Hesham ElBakoury <helbakoury at gmail.com>:
> Hi Christian,
> How you synchronize the time of the satellites in the network? Are you saying each satellite has a master clock?
> 
> Hesham
> 
> On Sat, Mar 2, 2024, 7:38 AM Christian von der Ropp <cvdr at vdr.net> wrote:
> Why not acquire the time directly from by the satellite terminal and run local NTP servers instead of syncing via the Internet? LEO satellite terminals always have onboard GNSS antennas for geolocation which is necessary to find the satellites, so integrating a local GNSS-disciplined Stratum-1 NTP server seems trivial to me.
> 
> 
> Am 2. März 2024 17:25:59 OEZ schrieb Hesham ElBakoury via Starlink <starlink at lists.bufferbloat.net>:
> Hi Sebastian,
> Can we still use PTP and NTP for time synchronization in  Satellite networks or we need new protocols? If we need new protocols, do such protocols exist?
> 
> Thanks
> Hesham
> 
> On Sat, Mar 2, 2024, 7:18 AM Sebastian Moeller <moeller0 at gmx.de> wrote:
> Hi Hesham
> 
> > On 2. Mar 2024, at 16:03, Hesham ElBakoury via Starlink <starlink at lists.bufferbloat.net> wrote:
> > 
> > Time synchronization, for satellite networks, faces several challenges:
> > 1. Signal Propagation Delays: Unlike terrestrial networks where signals travel through cables at the speed of light,
> 
> [SM] The speed of light in your typical glas fibers (and accidentally the information propagation speed in metallic conductors) comes in roughly at 2/3 of the speed of light in vacuum, while the speed of light in air at see level is a mere 90 KM/s slower than in vacuum. 
> 
> > satellite communication involves signals traveling vast distances through space. This creates significant delays.
> 
> [SM] Sure distances might be larger, but propagation speed is around 100000Km/s faster... my main point is speed of light is a) dependent on the medium b) not the things that differentiates space from the earth's surface here, but mere geometry and larger distances on larger spheres...
> 
> > 2. Clock Drift: Even highly precise atomic clocks, used in satellites, are susceptible to "drift" - gradually losing or gaining time. This drift, caused by factors like temperature variations, radiation exposure, and power fluctuations, can lead to inconsistencies in timekeeping across the network.
> > 3. Signal Degradation: As signals travel through space, they can degrade due to factors like atmospheric interference, ionospheric disturbances, and solar activity. This degradation can introduce noise and errors, impacting the accuracy of time synchronization messages. 
> > 4. Limited Resources: Satellites have limited power and processing capabilities. Implementing complex synchronization protocols can be resource-intensive, requiring careful optimization to minimize their impact on other functionalities.
> > 5. Evolving Technologies: As satellite technologies and applications continue to evolve, new challenges related to synchronization might emerge. For example, the integration of constellations with thousands of satellites poses unique synchronization challenges due to the sheer scale and complexity of the network.
> > These challenges necessitate the development of robust and efficient time synchronization protocols for satellite networks and an integrated satellite and  terrestrial networks
> > Are you aware of such time synchronization protocols?
> > I would think that using Satellite simulators is the most viable way to develop and test these protocols given that using satellites is not that easy.
> > Thanks
> > Hesham
> > 
> > 
> > 
> > _______________________________________________
> > Starlink mailing list
> > Starlink at lists.bufferbloat.net
> > https://lists.bufferbloat.net/listinfo/starlink
> 
> -- 
> Diese Nachricht wurde von meinem Android-Mobiltelefon mit K-9 Mail gesendet.
> -- 
> Diese Nachricht wurde von meinem Android-Mobiltelefon mit K-9 Mail gesendet.