Thang N. Dinh
Aug 9 · 3 min read

BackPackers, Fractal’s scaling solution, will be presented at Scaling Bitcoin 2019, Sep. 11th -12th in Tel Aviv University. Started in 2015 with the underwriting support of Massachusetts Institute of Technology, Chaincode Labs, Chain and Blockstream, Scaling Bitcoin has been one of the flagship venues for an academic approach surrounding the Bitcoin ecosystem. Among this year presenters are Pieter Wuille (Blockstream), Gregory Maxwell, Roger Wattenhofer (ETH Zurich), Andrew Miller (UIUC), David Tse (Stanford).

Scalingbitcoin, one of the flagship venues for academic and blockchain developers

BackPackers introduces a novel network paradigm to resolve several inefficiencies at the network layer (layer 0), including transaction broadcast bottleneck, source broadcast bottleneck, and unbalanced load among the nodes in the peer-to-peer (P2P) network.

BackPackers: A decentralized and secure Backbone of Packers

BackPackers provides the first decentralized and secure backbone network by introducing a new role, called packers. Packers, whose pseudo-identities are known to all, will form a decentralized network, similar to those used in the distributed hash tables (DHT). They will gather transactions from users and batch them into so-called pseudoblocks before broadcasting them into the network. Packers are incentivized by receiving a portion of relaying fee for transactions that they pack. They provide network-as-a-service (NaaS) and compete in a free market. Importantly, BackPackers is designed to provide the same guarantee on consistency and liveness as the underlying-blockchain, even when all packers are malicious.

Data dissemination flow in BackPackers

BackPackers guarantees the optimal propagation time, given the network topology and the link latency. Instead of propagating several MBs blocks, only meta-block, compact blocks of size 2–3KB, are gossiped along shortest paths to nodes in the P2P network with minimal verification. Each meta-block contains an ordered list of IDs of the selected pseudoblocks and solution for the “puzzle”. Upon receiving the meta-block and all the there-in referenced pseudoblocks, nodes in the network can linearize the pseudoblocks: (1) assemble the pseudoblocks together, and (2) resolve conflict and duplicate transactions. The propagation of the meta-block, however, requires only the verification on the solution (e.g. the nonce in Bitcoin).

Stochastic network optimization theory for near-optimal throughput

BackPackers comes with the first intelligent gossiping protocol that guarantees near-optimal throughput. The gossiping protocol automatically balances the load among neighbors of the nodes, prioritizing serving of nodes that are lagging behind their neighbors. By using stochastic network optimization theory, we show that the throughput converges to the
(1-ϵ) of the network capacity with the expected queue length O(1/ϵ).

In summary, BackPackers introduce a novel layer 0 scaling solution that provides provably optimal propagation time and near-optimal throughput. As the network-layer is currently either forgotten or under-explored, BackPackers stands out as an orthogonal scaling solution to those at layer 1 and 2.


Fractal Platform Inc

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