TSN implementation practical question

[nah1n]

Hello,

I am building a network, with 4 IE4000 switch and 10 end devices. All the end devices are pc with TSN enabled port. Now I have some question if you can help me that will be great.
1. In the network, who initiates the synchronization process among the TSN enabled devices?

2. In 802.1AS, PTP instance with the grandmaster clock has a connection with the source clock which provides the time, and gmRateratio and all the calculation starts with that. (see figure 1) Now in my case do I need to connect one of my switch/end device to a outside clock(GNSS/GPS)? If not then how the synchronization will be done? Can the local clock of a PTP instance considered a source clock? 

I know the questions are very theoritical, but if someone can answer, it will be a big help. Thanks

[VA.KI]

Hello,

For the first one you have to choose a master PC which will send synchronization command.

[nah1n]

Hello,

How to do that? Is there any command for that? 

[Jacobson-ni]

Any 802.1AS device should automatically initiate the synchronization process which looks very similar to how 1588 capable devices select their GM.

https://www.ieee802.org/1/files/public/docs2008/as-kbstanton-8021AS-overview-for-dot11aa-1108.pdf

I'm sure I'll be missing out on a bunch of details but the general flow as far as I understand is that once an 802.1AS capable device comes online it will just wait for a bit of time. If it doesn't hear anything then it will assume it's the GM and start broadcasting announce messages. If the device comes online and there are already devices synced over 802.1AS then the current GM will be broadcasting it's own announce message (the device basically waits when it starts up to see if there is an existing GM). If the current GM is better than the device which came online it will just sync to the existing GM. If the device determines that it is better than the current GM it will send out its own announce message, all other devices on the network will see that there is a better clock, and they will start syncing to that new device.

If the current GM drops off the network, all of the devices will eventually realize they don't have a GM and will start broadcasting their own announce messages, eventually settling on a new GM.

That's my understanding at least.

[nah1n]

Thank you.

Any feedback on the 2nd question?