isabella232 / student_19_tlc

Spring 2019 - Threshold Logical Clocks (TLC) prototype

TLC Protocol

Current implementations:

• "simple" version: no CoSi, acks are broadcast, blocking, O(N^3) messages
• "CoSi version": each node aggregates own acks, blocking, O(N^2) messages

Important Considerations: these implementations currently rely on eventual message delivery from the underlying communication links for their asynchronicity guarantees (e.g. tcp timeouts might pose a problem)

Usage

Each node/service that uses the protocol is responsible for broadcasting one message per round, including empty messages:

msg := []byte(fmt.Sprintf("This round's message for this node"))
pi.Message <- msg	// var pi *TLC

And can collect that round's set of messages:

set := <- pi.ThresholdSet // var set map[onet.TreeNodeID]*MessageDelivered

for node, msg := range set {
	if msg.TDelivered {
		println("The round %v message: %v, sent by node %v,
		was delivered by a threshold of nodes!", msg.Round, msg.Message, node)
	}
}

All of the messages returned in the round are of that round. Buffering of messages from future rounds (nodes further ahead) is done automatically.

Whenever a round finishes (i.e. when <- pi.ThresholdSet returns), the protocol waits for the validation function to be updated before it starts processing the next round's messages. You can signal that the function has been updated by either providing the next round's message (pi.Message <- msg) or through the tlc.ReadyForNextRound() method (useful in case you want to start processing other nodes' messages before your message is ready)

To terminate the local protocol instance "cleanly" (currently for testing purposes only).

pi.Terminate() // Should be done for each instance. Can be used to simulate crashes. 

For quick reference:

type MessageDelivered struct {
	Round   uint64
	Message []byte
	TDelivered bool // true if the message was delivered by TMsgs nodes ("certified")
}

Simulation(s)

You can define the behaviour of remote nodes a priori by modifying the Dispatch method of TLCWrapper.

The root node's behaviour is defined in the Run method.

Run a simulation with:

cd simulation/
go build
./simulation protocol.toml

Contact me (mvidigueira) if you have any problems.