Clarification: On-Change GNMI Subscription with Heartbeat Interval

[akshansh237]

Request Type:
GNMI On-Change Subscription with Heartbeat interval.

Expected Behavior from GNMI Specs:

1. Send full dump of data to tell the client of current state. Once done, send a sync_response which indicates to the client that initial data dump is done.
2. Only send updates/deletes if any lea if changed
3. Once heartbeat interval expires, send full dump of the current state again.

Use-case of heartbeat-interval:
My understanding is that this helps the client to re-sync every heartbeat interval with the server as some of the updates/deletes may have gone missing in the network due to packet drop.
Client can do mark and sweep when they receive such data.

Questions:
a) When step 3) is being executed by server, how does server indicate to the client that its now sending full data/current-state again ? I dont see any mark and sweep or start flags listed in the spec.
b) When does heartbeat interval timer start ? I assume its after we are done sending all data of current state.