[Starlink] Time Synchronization in Satellite Networks

[Hesham ElBakoury]

But how you address the issues I mentioned before such propagation delay,
clock drifting, and signal degradation, ...

Hesham

On Sat, Mar 2, 2024, 9:18 AM Alexandre Petrescu via Starlink <
starlink at lists.bufferbloat.net> wrote:

> some of the question is to what level of precision one wants the time to
> be maintained synchronized between entities, and for what application?
> Nano-second precision?  Less?  More is acceptable?  For what kind of
> application?  (I will not give examples).
>
> I think links with hundred ms latency range and NTP can easily maintain
> nano-second synch'ed precision, from experience with ground links.
>
>
> Le 02/03/2024 à 18:01, Alexandre Petrescu via Starlink a écrit :
> >
> > Le 02/03/2024 à 16:38, Christian von der Ropp via Starlink a écrit :
> >> Why not acquire the time directly from by the satellite terminal and
> >> run local NTP servers instead of syncing via the Internet?
> >
> > Certainly it is possible to run ntpd servers and clients on satellites
> > and maintain synchronized times.  I would be surprised if some of them
> > dont already do that.
> >
> > The performance characteristics of some links between some satellites
> > are not very different than links here on ground where NTP is run
> > routinely.
> >
> > NTP was designed and tested at a time when ground links had inferior
> > perf. characteristics than many satcom links of recent years.
> >
> > Alex
> >
> >
> >> 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
> >>         >
> >>         >
> >>         >
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> >>
> >> --
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> >> gesendet.
> >>
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