Re: [Starlink] Time Synchronization in Satellite Networks

[Hesham ElBakoury <helbakoury@gmail.com>]

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

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