Le 02/03/2024 à 18:26, Hesham ElBakoury a écrit :
But how you address the issues I mentioned before such propagation
delay, clock drifting, and signal degradation, ...
Propagation delay is what others call 'latency'. I believe the current
latencies in satcom links of many kinds allow for the use of NTP very
well. Clocks will sync with NTP in sats, but it depends of the
synchronisation precision needed.
Wouldnt you think so?
(clock drifting - if your source of information is an AI tool, then I
suggest to find a way to feed back to the AI tool. If possible, then I
suggest to explain to AI tool how clocks work; clocks drift often when
they travel very fast, much faster than how current sats travel, we talk
about aproaching speed of light, and sats dont; other times clocks drift
because of impurities in some of their hardware and stones - the sats
have the same hardware as on ground, so they are subject to same drift
as computers where current NTP is run; NTP actually _addresses_ that
clock drifting; even the fanciest non-stone but Cesium 'atomic' clocks
drift at some point, to a certain degree, on Earth - time is relative,
time is a concept of humans, there is no time just a 'long now' someone
said)
(signal degradation - signals dont degrade when they travel in space;
they might degrade with distance, but much less so as when they travel a
same distance on ground, be it on fiber)
(one asked two AI tools whether Beethoven met Liszt and one got
contradictory answers).
Alex
Hesham
On Sat, Mar 2, 2024, 9:18 AM Alexandre Petrescu via Starlink
<starlink@lists.bufferbloat.net> wrote:
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@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
>> >
>> >
>> >
>> > _______________________________________________
>> > Starlink mailing list
>> > Starlink@lists.bufferbloat.net
>> > https://lists.bufferbloat.net/listinfo/starlink
>>
>> --
>> Diese Nachricht wurde von meinem Android-Mobiltelefon mit K-9 Mail
>> gesendet.
>>
>> _______________________________________________
>> Starlink mailing list
>> Starlink@lists.bufferbloat.net
>> https://lists.bufferbloat.net/listinfo/starlink
> _______________________________________________
> Starlink mailing list
> Starlink@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/starlink
_______________________________________________
Starlink mailing list
Starlink@lists.bufferbloat.net
https://lists.bufferbloat.net/listinfo/starlink
_______________________________________________
Starlink mailing list
Starlink@lists.bufferbloat.net
https://lists.bufferbloat.net/listinfo/starlink
