How is node membership handled on Stellar?

Question

I'm looking through the whitepaper and getting a bit confused on an issue.

(3.2 Examples and discussion) mentions a tiered structural approach similar to the Internet with various Tier 1 nodes run by trusted/financial institutions with various levels of middle tiers. This paired with SCP giving maximum freedom in chosing which combinations of other participants to trust has be wondering the following:

How would a new node join as a tier 1 node or a tier 2 node and would all nodes see the same set of tier 1 or 2 nodes or only a subset?

Answer 1

Each node defines which other ones it trusts for the quorum.

The layers are a good example for a model how to organise whom to trust. But on the technical side there are just node addresses and thresholds defined. When you want to add a new node to your "layer", you would need to add it to the QUORUM_SET in Core config.