Hi Hesham,
> On 2. Apr 2024, at 00:04, Hesham ElBakoury <helbako...@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 <c...@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 <helbako...@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 <c...@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@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 <moell...@gmx.de> wrote:
> Hi Hesham
>
> > On 2. Mar 2024, at 16:03, Hesham ElBakoury via Starlink
> > <starlink@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
> >
> >
> >
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