Tezos_baseSourceA locator t is a data structure which roughly represents a list of block hashes in the chain. These hashes go from the top of the chain to the bottom. It is sparse in the sense that the distance between two hashes increases exponentially when we move away from the head.
Distributed_db protocol version.
Tezos Shell Module - Mempool, a.k.a. the operations safe to be broadcast.
P2p-layer protocol version.