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Wavefront

The wavefront protocol is an initiate exchange exchange protocol, used for gossip in the tagion hashgraph.

Node Alpha initiates a connections and sends it's initial known heights.
Node Beta sends the difference between heights Alpha and it's own known heights.
Node Alpha sends the difference between Betas calculated heights and it's own heights.

The ideas and goals of the wavefront protocol are better described in the Tagion whitepaper. tagion whitepaper* diagram explaining the wavefront from tagion whitepaper

The different wavefront exchange states are defined here. tagion.hashgraph.HashGraphBasic.ExchangeState

The wavefront record communicated between nodes is defined here. tagion.hashgraph.HashGraphBasic.Wavefront

The hirpc protocol is described here https://hibon.org/posts/hirpc

Each hirpc package is put in an Envelope which takes care of compression and encryption.

Communication rules between a pair nodes

The nodes communicate over a single wire in a half-duplex style.
The priority of the rules are in the order they appear. A prior rule takes precedency over a later rule.
The keywords MAY, SHOULD and MUST, indicate the requirement levels of the rule. In accordance to https://datatracker.ietf.org/doc/html/rfc2119
MAY means that the node is free to do this at will.
SHOULD means that the node is strongly encouraged to do this, but the rule is NOT violated if not complied with.
MUST means that the node is obliged to follow this rule.

IF a communication error or rule violation occurs the connection MUST be closed.  
A node SHOULD keep the connection open until a hirpc result or an hirpc error is exchanged,
then the connection MUST be closed.  

A node MAY initiate a connection with any node.
A node which initiates a connection MUST send a message and it MUST sent the first message.  
The first message MUST be a hirpc method.  
Any hirpc method MUST be answered with another hirpc method OR a hirpc result OR a hirpc error.

Wavefront response patterns

method SHARP -> result COHERRENT | result RIPPLE
method TIDAL WAVE -> error | method FIRST WAVE
method FIRST WAVE -> error | result SECOND WAVE
* -> error