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
>
>
>
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