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@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@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 > >> > > >> > > >> > > >> > _______________________________________________ > >> > Starlink mailing list > >> > Starlink@lists.bufferbloat.net > >> > https://lists.bufferbloat.net/listinfo/starlink > >> > >> -- > >> Diese Nachricht wurde von meinem Android-Mobiltelefon mit K-9 Mail > >> gesendet. > >> > >> _______________________________________________ > >> Starlink mailing list > >> Starlink@lists.bufferbloat.net > >> https://lists.bufferbloat.net/listinfo/starlink > > _______________________________________________ > > Starlink mailing list > > Starlink@lists.bufferbloat.net > > https://lists.bufferbloat.net/listinfo/starlink > _______________________________________________ > Starlink mailing list > Starlink@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/starlink >
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