This article is one part of a longer deep dive into Leios, Cardano’s proposed consensus upgrade. The full post is available at https://314pool.com/post/leios. We’ve broken it into smaller, standalone reads to make it more accessible for the Cardano Cube audience.
Leios runs as a “pipelined” protocol, where the same protocol is run multiple times currently, shifted relative to each other in time. You can picture this as when a chorus sings in “rounds”.
A single pipeline is divided into several stages, each of which lasts a number of slots. The next pipeline begins after the previous one finishes its first stage.
In the first stage, nodes across the network generate high frequency (1-5 per second) fairly large (~100-300 kilobyte) “Input Blocks” each of which contains user transactions, and diffuses them throughout the network.
In the second stage, nodes produce an “Endorsement Block”, which references a set of input blocks that are valid with reference to some recent ledger state. These endorsement blocks are diffused throughout the network. The “Endorsement Block” also references other, recent endorsement blocks from past pipelines.
In the third stage, as nodes observe a new endorsement block and validate it themselves, they sign a “vote” for the endorsement block and diffuse those votes throughout the network.
In the final stage, as nodes get elected to produce a normal Praos block (now called a “Ranking Block”), they select an endorsement block that has received votes from 70% of the active stake, and produce a compact certificate proving the endorsement block is reliable, and include that in the Ranking Block.
This is a mostly faithful description of the version of Leios described in the research paper. There are some other small devils in the details, such as the timing on these different phases, how long an input block is valid, etc., and some changes that the Leios team is exploring as part of their R&D efforts, but I’ll refer to you to the specification or our simulation work for these specifics instead of bloating this already fairly lengthy blog post.