[Starlink] Time Synchronization in Satellite Networks

[Alexandre Petrescu]

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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