[Starlink] Time Synchronization in Satellite Networks
Alexandre Petrescu
alexandre.petrescu at gmail.com
Sat Mar 2 12:18:00 EST 2024
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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