Chapter overview:
  * high level description of p2p interaction for the LN

Relevant questions to answer:
  * Encrypted P2P Transport:
      * What is the noise protocol? How does it differ from TLS? Who created it

      * and what are some of primary design principles?

      * What is an authenticated key exchange?

      * Why does Noise offer various handshakes? What are some of unique properties certain handshakes offer?

      * What is key rotation in the context of a complete handshake? Why is it important?

      * What is "brontide"? How is it used in LN today? How can it be upgraded in the future?
  * LN Message Format:

      * What kind of framing is used in the LN message format? What's the max message size and why is it in place?

      * What is a varint? Why is it used in the protocol?

      * What are the message types of some of the popular messages in the protocol?

      * How can new messages be added in the future?
  * Feature bits:

      * What are feature bits in the network, and how+where are they advertised?

      * How can feature bits be used to phase in new features to the protocol?

      * Today, what are some of the major feature bits used in the system?

      * What's the difference between and end-to-end network upgrade and an internal network upgrade? How's the analogous to the evolution of routers and protocols in the existing internet?

  * TLV Message Extensions:

      * What does TLV stand for?

      * How is this related to the existing protobuf message format?

      * Where are TLV fields used in the protocol today?

      * How can TLV fields be used to extend the protocol, existing messages, and the onion itself?
