<div dir="auto">But how you address the issues I mentioned before such propagation delay, clock drifting, and signal degradation, ...<div dir="auto"><br></div><div dir="auto">Hesham</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sat, Mar 2, 2024, 9:18 AM Alexandre Petrescu via Starlink <<a href="mailto:starlink@lists.bufferbloat.net">starlink@lists.bufferbloat.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">some of the question is to what level of precision one wants the time to <br>
be maintained synchronized between entities, and for what application? <br>
Nano-second precision? Less? More is acceptable? For what kind of <br>
application? (I will not give examples).<br>
<br>
I think links with hundred ms latency range and NTP can easily maintain <br>
nano-second synch'ed precision, from experience with ground links.<br>
<br>
<br>
Le 02/03/2024 à 18:01, Alexandre Petrescu via Starlink a écrit :<br>
><br>
> Le 02/03/2024 à 16:38, Christian von der Ropp via Starlink a écrit :<br>
>> Why not acquire the time directly from by the satellite terminal and <br>
>> run local NTP servers instead of syncing via the Internet?<br>
><br>
> Certainly it is possible to run ntpd servers and clients on satellites <br>
> and maintain synchronized times. I would be surprised if some of them <br>
> dont already do that.<br>
><br>
> The performance characteristics of some links between some satellites <br>
> are not very different than links here on ground where NTP is run <br>
> routinely.<br>
><br>
> NTP was designed and tested at a time when ground links had inferior <br>
> perf. characteristics than many satcom links of recent years.<br>
><br>
> Alex<br>
><br>
><br>
>> LEO satellite terminals always have onboard GNSS antennas for <br>
>> geolocation which is necessary to find the satellites, so integrating <br>
>> a local GNSS-disciplined Stratum-1 NTP server seems trivial to me.<br>
>><br>
>><br>
>> Am 2. März 2024 17:25:59 OEZ schrieb Hesham ElBakoury via Starlink <br>
>> <<a href="mailto:starlink@lists.bufferbloat.net" target="_blank" rel="noreferrer">starlink@lists.bufferbloat.net</a>>:<br>
>><br>
>> Hi Sebastian,<br>
>> Can we still use PTP and NTP for time synchronization in<br>
>> Satellite networks or we need new protocols? If we need new<br>
>> protocols, do such protocols exist?<br>
>><br>
>> Thanks<br>
>> Hesham<br>
>><br>
>> On Sat, Mar 2, 2024, 7:18 AM Sebastian Moeller <<a href="mailto:moeller0@gmx.de" target="_blank" rel="noreferrer">moeller0@gmx.de</a>><br>
>> wrote:<br>
>><br>
>> Hi Hesham<br>
>><br>
>> > On 2. Mar 2024, at 16:03, Hesham ElBakoury via Starlink<br>
>> <<a href="mailto:starlink@lists.bufferbloat.net" target="_blank" rel="noreferrer">starlink@lists.bufferbloat.net</a>> wrote:<br>
>> ><br>
>> > Time synchronization, for satellite networks, faces several<br>
>> challenges:<br>
>> > 1. Signal Propagation Delays: Unlike terrestrial networks<br>
>> where signals travel through cables at the speed of light,<br>
>><br>
>> [SM] The speed of light in your typical glas fibers (and<br>
>> accidentally the information propagation speed in metallic<br>
>> conductors) comes in roughly at 2/3 of the speed of light in<br>
>> vacuum, while the speed of light in air at see level is a mere<br>
>> 90 KM/s slower than in vacuum.<br>
>><br>
>> > satellite communication involves signals traveling vast<br>
>> distances through space. This creates significant delays.<br>
>><br>
>> [SM] Sure distances might be larger, but propagation speed is<br>
>> around 100000Km/s faster... my main point is speed of light is<br>
>> a) dependent on the medium b) not the things that<br>
>> differentiates space from the earth's surface here, but mere<br>
>> geometry and larger distances on larger spheres...<br>
>><br>
>> > 2. Clock Drift: Even highly precise atomic clocks, used in<br>
>> satellites, are susceptible to "drift" - gradually losing or<br>
>> gaining time. This drift, caused by factors like temperature<br>
>> variations, radiation exposure, and power fluctuations, can<br>
>> lead to inconsistencies in timekeeping across the network.<br>
>> > 3. Signal Degradation: As signals travel through space, they<br>
>> can degrade due to factors like atmospheric interference,<br>
>> ionospheric disturbances, and solar activity. This degradation<br>
>> can introduce noise and errors, impacting the accuracy of time<br>
>> synchronization messages.<br>
>> > 4. Limited Resources: Satellites have limited power and<br>
>> processing capabilities. Implementing complex synchronization<br>
>> protocols can be resource-intensive, requiring careful<br>
>> optimization to minimize their impact on other functionalities.<br>
>> > 5. Evolving Technologies: As satellite technologies and<br>
>> applications continue to evolve, new challenges related to<br>
>> synchronization might emerge. For example, the integration of<br>
>> constellations with thousands of satellites poses unique<br>
>> synchronization challenges due to the sheer scale and<br>
>> complexity of the network.<br>
>> > These challenges necessitate the development of robust and<br>
>> efficient time synchronization protocols for satellite<br>
>> networks and an integrated satellite and terrestrial networks<br>
>> > Are you aware of such time synchronization protocols?<br>
>> > I would think that using Satellite simulators is the most<br>
>> viable way to develop and test these protocols given that<br>
>> using satellites is not that easy.<br>
>> > Thanks<br>
>> > Hesham<br>
>> ><br>
>> ><br>
>> ><br>
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