Re: [questions] Local ST 1 (GPS/GNSS) servers are consistently offset from internet ST1/2

[Mike G]

maybe the server checking your server is off a little...? I avg between 1.3 and 3.0 ms On 12/3/2022 1:53 PM, vom513 wrote: Hello all, This has been bugging me for a bit - but not enough till now to post a message :) I have two boxes here at home (this is “hobbyist” grade gear, not big commercial appliances). My hardware is: SyncBOX - https://www.worldtimesolutions.com/products/gps_time_server.html This is connected to a small “Jetway” x86 mini PC via DB9 / real UART serial. UPUTronics Pi Hat - https://thepihut.com/products/raspberry-pi-gps-hat It’s on a Pi obviously (3B I think) Both of these appear to be very stable. I graph the offset in MRTG and they both average about +/- 1-2 us. However - when I compare them each individually to a list of about 10 public ST1 and ST2 servers, they both are averaging about -3.5 ms offset. I did this with ntpdate -q and punched the values into Excel. To also back this data up - I feed a public pool member with these two guys - and my graphs on the server management page also show ~ -3.5 ms offset. (These are the same box…) https://www.ntppool.org/scores/216.143.11.126 https://www.ntppool.org/scores/2607:ff70:11::10 Also - ignore the scatter up above 0. I recently set prefer on both these guys to nail them down and track the pool graphs. So while I guess 3ms isn’t the end of the world, I’m just scratching my head as to why both my boxes are consistent with this offset from the “world”. I suppose I could config both to offset by this amount in their config, but that seems a bit heavy handed. I’d much rather understand why they both converge at this offset. Thanks in advance for any info and clue. PS: Something I just thought of before I hit send… Both of these are behind my home cable modem. And while the jitter is actually pretty good, I know there is inherent latency and jitter in most current DOCSIS networks. I think DOCSIS 3.1 has some really nice bufferbloat / latency / jitter “fixes” (AQM I think it’s called) - but my provider isn’t there yet (and I’m on Docsis 3.0 anyway). Could this be it ?