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Author: Admin | 2025-04-28
C which has sj′ as its previous hash, receives the communication, it will compute sj=SHA256(SHA256(ni+hi+sj′)).If sj is a valid solution according to the rules of Section 1.2.2 then miner Mj will add block Bi to its blockchain C, abandon the block Bj that it is working on and commence trying to add a block to the chain CBi. Any transactions in Bj that are not in Bi will be incorporated into this new block. Importantly, miners Mi and Mj now have identical versions of the blockchain.The existence of communication delays can upset the above process, because blocks can be discovered while communication and validation is in process. Decker and Wattenhofer [1] measured the difference between the time that a node announced the discovery of a new block or a transaction and the time that it was received by other nodes for a period of operation in the actual Bitcoin network. They observed that the median time until a node receives a block was 6.5 s, the mean was 12.6 s and the 95th percentile of the distribution was around 40 s. Moreover, they showed that an exponential distribution provides a reasonable fit to the unconditional communication delay distribution.Suppose all miners are working on the same version C of the blockchain and miner Mi mines block Bi at time t. It will then add Bi to the blockchain C and broadcast block Bi to all its peers. Suppose that this communication reaches miner Mj at time t+δj and that Mj has mined a block Bj at time t′∈[t,t+δj).Miner Mj now knows about two versions CBi and CBj of the blockchain, which are of the same length. From the point of view of Miner Mj, the blockchain has split, and we can think of the node as being in a ‘race’ to see which version of the blockchain survives.Miner Mi will build on CBi because this is the version of the blockchain that it knew about first. However, miner Mj knew about CBj first, and will attempt to build on this version of the blockchain. Other miners will work on either CBi or CBj depending on which version they heard about first. The ‘race’ situation is resolved when the next block B∗ is mined, say on CBi, and communicated via the peer network. Then CBiB∗ will be longer than CBj and all miners will eventually start building on CBiB∗. It is then
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