Blocks and tipsets

Like many other blockchains, blocks are a fundamental concept in Filecoin. However, unlike other blockchains, Filecoin is a chain of groups of blocks called tipsets, rather than a chain of individual blocks. This page discusses blocks, tipsets, their relationship to each, and their use in Filecoin in detail.

Blocks #

In Filecoin, a block consists of:

• A block header
• A list of messages contained in the block
• A signed copy of each message listed

Every block refers to at least one parent block; that is, a block produced in a prior epoch.

A message represents communication between two actors, and thus changes in network state. The messages are listed in their order of appearance, deduplicated and returned in canonical order of execution. So, in other words, a block describes all changes to the network state in a given epoch.

Tipsets #

As described in Consensus, multiple potential block producers may be elected via Expected Consensus (EC) to create a block in each epoch, which means that more than one valid block may be produced in a given epoch. All valid blocks with the same height and same parent block are assembled into a group called a tipset.

Benefits of tipsets #

In other blockchains, blocks are used as the fundamental representation of network state; that is, the overall status of each participant in the network at a given time. However, this structure has the following disadvantages:

• Potential block producers may be hobbled by network latency.
• Not all valid work is rewarded.
• Decentralization and collaboration in block production is not incentivized.

Because Filecoin is a chain of tipsets rather than individual blocks, the network enjoys the following benefits:

• All valid blocks generated in a given round are used to determine network state, increasing network efficiency and throughput.
• All valid work is rewarded (that is, all validated block producers in an epoch receive a block reward).
• All potential block producers are incentivized to produce blocks, disincentivizing centralization and promoting collaboration.
• Because all blocks in a tipset have the same height and parent, Filecoin is able to achieve rapid convergence in the case of forks.

In summary, blocks, which contain actor messages, are grouped into tipsets in each epoch, which can be thought of as the overall description of network state for a given epoch.

Tipsets in the Ethereum JSON-RPC #

Wherever you see the term block in the Ethereum JSON-RPC, you should mentally read tipset. Before the inclusion of the Filecoin EVM-runtime, there was no single hash referring to a tipset. A tipset ID was the concatenation of block CIDs, which led to a variable length ID, and poor user experience.

With the Ethereum JSON-RPC, we introduced the concept of the tipset CID for the first time. It is calculated by hashing the former tipset key using a blake-256 hash. Therefore, when you see the term:

• block hash, think tipset hash.
• block height, think tipset epoch.
• block messages, think messages in all blocks in a tipset, in their order of appearance, deduplicated and returned in canonical order of execution.