Hi NTP brings along a bunch of “baggage” that gets you out of the category of “couple of lines of code” protocol. What I’m suggesting is very much the same thing as a GPS sentence. Sent once a second with a very minimal payload. You just are doing it via UDP instead of RS-232 serial.
Bob > On Aug 15, 2019, at 11:35 AM, Tim Shoppa <[email protected]> wrote: > > Bob, ntpd for ages has supported broadcast/multicast UDP. > https://www.eecis.udel.edu/~mills/ntp/html/assoc.html#broad > > If you care about security it's like a bag of angry cats. And the > one-way-ness removes the ability to measure round-trip delay. So it's > pretty rare to see it being used well. > > Tim N3QE > > On Thu, Aug 15, 2019 at 11:08 AM Bob kb8tq <[email protected]> wrote: > >> Hi >> >> Which all sort of begs the question: >> >> Why not a simple “broadcast UDP” once a second time packet approach for a >> home LAN? >> >> Unless you get really crazy, it’s not going to be a very big packet. >> Seconds since some >> arbitrary point in time. Time zone offset. Maybe a leap second count. >> Server ID maybe. >> Less than 100 bytes not including the overhead. >> >> Bob >> >>> On Aug 15, 2019, at 5:36 AM, Hal Murray <[email protected]> wrote: >>> >>> >>> [email protected] said: >>>> I am a newbie and am wondering what options there are for exchanging >> time >>>> on a more basic level than NTP or PTP (that is for situations when a >>>> full network stack is too complex). >>> >>> You haven't described your problem fully yet. >>> >>> Are you interested in client side or server side? (or both) >>> >>> What sort of environment are you working in? What sort of hardware do >> you >>> have available? >>> >>> NMEA over a serial port is probably what you want, but... >>> >>> >>> Raspberry Pi and similar are not very expensive. They come with >> networking >>> software. The Pi isn't very nice for time-nut work over the net because >> the >>> Ethernet is on USB which adds jitter and/or hanging bridges. It does >> have >>> GPIO. >>> >>> >>> There is a lot of things you can do without a "full network stack". >>> >>> What level of hacking is reasonable depends on your environment. For a >> setup >>> at home, you are unlikely to annoy anybody else. >>> >>> The Alto firmware could boot over the (3 MB) Ethernet. The boot servers >> would >>> periodically send a boot-loader packet to a reserved hardware address. >> The >>> firmware only had to setup the hardware to receive a packet, wait for >> one, >>> sanity check things, and jump to it. >>> >>> If you use UDP rather than TCP, the "stack" level packet format is much >>> simpler. Retransmission becomes trivial if you only have one un-ACKed >> packet >>> to consider. Performance on a LAN is OK most of the time. >>> >>> For something like a NTP server, you can avoid routing and ARP by >> sending the >>> reply back where it came from. >>> >>> For the client side, the normal problem is finding the server. If you >> only >>> have one server, you can wire in the address. >>> >>> >>> >>> >>> -- >>> These are my opinions. I hate spam. >>> >>> >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>> and follow the instructions there. >> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
