Network Protocol 2
Building a low-latency network requires P2P nodes that have low-latency connections and a protocol designed to minimize latency. for the purpose of this document we will assume that two nodes are located on opposite sides of the globe with a ping time of 250ms.
Announce, Request, Send Protocol
Under the prior network archtiecture, transactions and blocks were broadcast in a manner similar to the Bitcoin protocol: inventory messages notify peers of transactions and blocks, then peers fetch the transaction or block from one peer. After validating the item a node will broadcast an inventory message to its peers.
Under this model it will take 0.75 seconds for a peer to communicate a transaction or block to another peer even if their size was 0 and there was no processing overhead. This level of performance is unacceptable for a network attempting to produce one block every second.
This prior protocol also sent every transaction twice: initial broadcast, and again as part of a block.
To minimize latency each node needs to immediately broadcast the data it receives to its peers after validating it. Given the average transaction size is less than 100 bytes, it is almost as effecient to send the transaction as it is to send the notice (assuming a 20 byte transaction id)
Each node implements the following protocol:
onReceiveTransaction( from_peer, transaction ) if( isKnown( transaction.id() ) ) return markKnown( transaction.id() ) if( !validate( transaction ) ) return for( peer : peers ) if( peer != from_peer ) send( peer, transaction ) onReceiveBlock( from_peer, block_summary ) if( isKnown( block_summary ) return full_block = reconstructFullBlcok( from_peer, block_summary ) if( !full_block ) disconnect from_peer markKnown( block_summary ) if( !pushBlock( full_block ) ) disconnect from_peer for( peer : peers ) if( peer != from_peer ) send( peer, block_summary ) onHello( new_peer, new_peer_head_block_num ) replyHello( new_peer ) // ack the hello message with our timestamp to measure latency if( peers.size() >= max_peers ) send( new_peer, peers ) disconnect( new_peer ) return while( new_peer_head_block_num < our_head_block_num ) sendFullBlock( new_peer, ++new_peer_head_block_num ) new_peer.synced = true for( peer : peers ) send( peer, new_peer ) onHelloReply( from_peer, hello_reply ) update_latency_measure, disconnect if too slow onReceivePeers( from_peer, peers ) addToPotentialPeers( peers ) onUpdateConnectionsTimer if( peers.size() < desired_peers ) connect( random_potential_peer ) onFullBlock( from_peer, full_block ) if( !pushBlock( full_block ) ) disconnect from_peer onStartup init_potential_peers from config start onUpdateConnectionsTimer