[time-nuts] IEEE1588

[Heinzmann, Stefan (ALC NetworX GmbH)]

> Chris Albertson wrote:

> The combination of a network server and a GPS receiver is called a
> "Grand Master".   It is not expensive to set one up.  Any low-end PC
> hardware that has a real serial port and then a good timing grade GPS.
>   You can't get away from the need to have at least one GPS recever but
> PTP can make it so you only need one receiver on your local LAN.

There's no requirement for a grandmaster to be hooked up to GPS. It may just as well work off its own oscillator. A grandmaster is the ultimate source of time in a PTP network. It is not relevant what its time source is.

There's also the notion of a master. A master is one of the modes a network port may be in. Of course, the network port of an active grandmaster is in master mode. But there may be other devices in the network which are slave on one of their network ports, and master on the others. Such devices are called "boundary clock" in PTP terminology, and they pass on the time received on the slave port to the master ports. They can be used to offload traffic from the grandmaster, for example.


Cheers
Stefan