[Starlink] Time Synchronization in Satellite Networks
Hesham ElBakoury
helbakoury at gmail.com
Mon Apr 1 18:04:18 EDT 2024
Hi Christian,
The problems is that Satellites move, therefore, the delay between the
different directions is different which violates the condition to run NTP
and PTP.
Hesham
On Sat, Mar 2, 2024, 8:19 AM Christian von der Ropp <cvdr at vdr.net> wrote:
> Hi Hesham,
>
> You do not acquire the time from a LEO satellite but directly from the GPS
> satellites which carry an atomic clock on board.
> I'd not be aware of any LEO providing a GNSS signal but Xona plan such
> system (although not carrying proper atomic clocks but probably chip-sized
> atomic clocks that require frequent syncing with proper atomic clocks):
> https://twitter.com/Megaconstellati/status/1708091536439673323
>
> There are efforts to build trapped-ion quantum clocks that are expected to
> become significantly smaller and cheaper than traditional atomic clocks
> while as accurate which would make it viable to put an atomic
> clock-equivalent on small LEO satellites. Once that happens you would have
> an independent alternative to the big GNSS birds in MEO but with stronger
> signals. I'm told that we are 5-10 years away from such trapped-ion quantum
> clocks.
>
> But for NTP clients, the described method (running a local NTP server in
> the satellite terminal synced to GPS) should be good enough.
>
> Christian
>
>
> Am 2. März 2024 18:02:47 OEZ schrieb Hesham ElBakoury <
> helbakoury at gmail.com>:
>
>> Hi Christian,
>> How you synchronize the time of the satellites in the network? Are you
>> saying each satellite has a master clock?
>>
>> Hesham
>>
>> On Sat, Mar 2, 2024, 7:38 AM Christian von der Ropp <cvdr at vdr.net> wrote:
>>
>>> Why not acquire the time directly from by the satellite terminal and run
>>> local NTP servers instead of syncing via the Internet? 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
>>>>> >
>>>>> >
>>>>> >
>>>>> > _______________________________________________
>>>>> > Starlink mailing list
>>>>> > Starlink at lists.bufferbloat.net
>>>>> > https://lists.bufferbloat.net/listinfo/starlink
>>>>>
>>>>> --
>>> Diese Nachricht wurde von meinem Android-Mobiltelefon mit K-9 Mail
>>> gesendet.
>>>
>> --
> Diese Nachricht wurde von meinem Android-Mobiltelefon mit K-9 Mail
> gesendet.
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.bufferbloat.net/pipermail/starlink/attachments/20240401/cb74ee16/attachment.html>
More information about the Starlink
mailing list