Performability evaluation of BFT protocols for DLT

The importance and interest about distributed systems as known an impulse, fol- lowing the widespread appearance of distributed ledger technologies, in particular blockchains. Researchers and developers have determined that a main source of performance bottlenecks in the distributed system can be attributed to the con- sensus protocol employed. In this thesis, it is presented the multi-criteria decision- making process adopted to select a suitable consensus protocol to be used under given conditions and requirements dictated by an arbitrary use scenario for the sys- tem under development. Subsequently, two analytical models to assess availability and performability of Byzantine fault-tolerant protocols are discussed and applied. The main results include the measurement of availability when the occurrence of malicious nodes in the network follows an arbitrary probability distribution, and the estimation of performability metrics for Byzantine fault-tolerant protocols. In particular, it emerges that all the evaluated quantities are non-linearly dependent on the defined parameters, e.g. the total number of nodes and the transactions service rate. Notably, the results from the analytical evaluation correctly replicates the trend of empirical studies found in literature, even though the values from the models and from the benchmarks are not consistently matching.