From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from sainfoin-smtp-out.extra.cea.fr (sainfoin-smtp-out.extra.cea.fr [132.167.192.228]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 640E43CB37 for ; Sat, 2 Mar 2024 12:18:01 -0500 (EST) Received: from pisaure.intra.cea.fr (pisaure.intra.cea.fr [132.166.88.21]) by sainfoin-sys.extra.cea.fr (8.14.7/8.14.7/CEAnet-Internet-out-4.0) with ESMTP id 422HI0NL006091 for ; Sat, 2 Mar 2024 18:18:00 +0100 Received: from pisaure.intra.cea.fr (localhost [127.0.0.1]) by localhost (Postfix) with SMTP id 5BE8A20D8E9 for ; Sat, 2 Mar 2024 18:18:00 +0100 (CET) Received: from muguet1-smtp-out.intra.cea.fr (muguet1-smtp-out.intra.cea.fr [132.166.192.12]) by pisaure.intra.cea.fr (Postfix) with ESMTP id 5504620D8E5 for ; Sat, 2 Mar 2024 18:18:00 +0100 (CET) Received: from [10.11.240.6] ([10.11.240.6]) by muguet1-sys.intra.cea.fr (8.14.7/8.14.7/CEAnet-Internet-out-4.0) with ESMTP id 422HI0ds050135 for ; Sat, 2 Mar 2024 18:18:00 +0100 Message-ID: <46eccea2-0fbd-46df-b0cc-70691d4a75f4@gmail.com> Date: Sat, 2 Mar 2024 18:18:00 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Content-Language: fr To: starlink@lists.bufferbloat.net References: <9a4e1bb4-0591-40f7-b072-8a1abd60f315@gmail.com> From: Alexandre Petrescu In-Reply-To: <9a4e1bb4-0591-40f7-b072-8a1abd60f315@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-CEA-Virus: SOPHOS_SAVI_ERROR_OLD_VIRUS_DATA Subject: Re: [Starlink] Time Synchronization in Satellite Networks X-BeenThere: starlink@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: "Starlink has bufferbloat. Bad." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 02 Mar 2024 17:18:01 -0000 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 >> : >> >>     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 >>     wrote: >> >>         Hi Hesham >> >>         > On 2. Mar 2024, at 16:03, Hesham ElBakoury via Starlink >>         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