The time in Cardano according to Ouroboros

3 min readMar 9, 2021


Cardano has PoS (proof of stake) as its consensus protocol and Ouroboros is the algorithm.

Ouroboros Classic was the first implementation, then Ouroboros BFT (Byzantine Fault Tolerance) which was the transition to the Shelley release and, with it, its decentralization.

The next innovation was Ouroboros Praos, which is based on Ouroboros Classic but provided substantial security and scalability improvements.

Ouroboros Genesis evolves Ouroboros Praos and allows parties to start from a genesis block, without the need for trust checkpoints or assumptions about past availability.

Finally Ouroboros Hydra which will be an off-chain scalability architecture, addresses three key challenges: high transaction throughput, low latency and minimal storage per node.


The broadest unit of measurement that divides the Cardano blockchain, are eras, which establish changes in network performance, through hard forks for implementation.

The eras are implemented according to the roadmap, and simultaneously between them, where the times depend on the development and success in the testnet.

Byron was its foundation, from 2017 to July 2020, which Shelley started, with the task of decentralization, allowing in the network the action of private pools to sign blocks.

Then Goguen, with the goal of the development of smart contracts, starting in phases, with the first hard fork Allegra at the end of 2020, then Mary in March 2021 and finally it will be Alonzo in mid-2021.

In parallel, the governance of the Voltaire era is being developed, with the Catalyst project, voting on proposals from the community to distribute funds for their development.

The Basho era, which refers to scalability, has Hydra as its main implementation, a second-layer solution on top of the Cardano protocol to accelerate it.

Blocks, epochs and slots

Ouroboros divides time into epochs. Each epoch lasts 5 days, and currently includes 432,000 slots, (5 days x 24 hours x 60 minutes x 60 seconds).

On average, one node is expected to be nominated every 20 seconds, for a total of 21,600 nominations per epoch. If randomly chosen slot leaders produce blocks, each block will be added to the chain. The remaining candidate blocks will be discarded.

Thus in each epoch approximately 21,600 blocks are created, but due to the randomness implemented in the protocol more or less blocks can be created.

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