On Mon, June 24, 2019 6:46 am, Christoph Kuhr wrote:
 What is the need for a specific GM if you AVB switch is down?
 Thus, one of the AVB switches involved should be the GM. The "core-most"
 switch in particular.

 Or  can someone think of a scenario, where this does not make sense?

If you have a higher quality device (for example a network master clock
connected to GPS disciplined oscillator for high stability).  In that case
the device should advertise a higher quality and should be selected as
master clock in any case.
One other case which comes to mind is if you want a multi-protocol device
to be master for a mixed system, so a single device providing synchronized
802.1AS for AVB devices, and layer 3 1588 messages for layer 3 devices.
Definitely starts getting into specialized cases, and you should be able
to set the clock quality field on a specialized clock source like that so
that it always wins the best master clock vote.