We identify the following protocol unit categories:
- Data Availability: Protocol units concerned with enabling the secure submission and ordered retrieval of transaction data to and from a network. Light node clients and servers are members of this category.
- Mempool: Protocol units concerned with the acceptance and ordering of transactions in a network prior to consensus. Mempool modules are members of this category.
- Sequencing: Protocol units concerned with consensus on the order of transactions in a network. Sequencer node implementations are members of this category.