Re: [Starlink] Time Synchronization in Satellite Networks

[Hesham ElBakoury <helbakoury@gmail.com>]

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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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