digraph {

size=6.25;
rankdir=LR
node [ shape = "box" ]
splines = ortho;
//ranksep = 10;
nodesep = 0.5;

p2pnetwork [ label = "P2P\nNetwork" ]
asic0 [ label = "ASIC" ];
software [ label = "Mining\nSoftware" ]
pool0 [ label = "Mining\nPool" ];

pool0 -> software [ label = "Prototype\nBlock→" ];
p2pnetwork -> pool0 [ label = "TXes→" ];
pool0 -> p2pnetwork [ label = "←Blocks" ];

software -> asic0 [ label = "Block\nHeaders &\nTargets→" ];
asic0 -> software [ label = "←Headers\nBelow\nTarget" ];

software -> pool0 [ constraint = false, label = "←Shares" ];

label = "Pool-Based Bitcoin Mining Workflow"
}