Update book for Turbine (#4583)

book/src/SUMMARY.md

@@ -16,7 +16,7 @@
   - [Leader Rotation](leader-rotation.md)
   - [Fork Generation](fork-generation.md)
   - [Managing Forks](managing-forks.md)
-  - [Data Plane Fanout](data-plane-fanout.md)
+  - [Turbine Block Propagation](turbine-block-propagation.md)
   - [Ledger Replication](ledger-replication.md)
   - [Secure Vote Signing](vote-signing.md)
   - [Stake Delegation and Rewards](stake-delegation-and-rewards.md)

book/src/turbine-block-propagation.md

@@ -1,12 +1,12 @@
-# Data Plane Fanout
+# Turbine Block Propagation
 
-A Solana cluster uses a multi-layer mechanism called *data plane fanout* to
-broadcast transaction blobs to all nodes in a very quick and efficient manner.
-In order to establish the fanout, the cluster divides itself into small
-collections of nodes, called *neighborhoods*. Each node is responsible for
-sharing any data it receives with the other nodes in its neighborhood, as well
-as propagating the data on to a small set of nodes in other neighborhoods. 
-This way each node only has to communicate with a small number of nodes.
+A Solana cluster uses a multi-layer block propagation mechanism called *Turbine*
+to broadcast transaction blobs to all nodes with minimal amount of duplicate
+messages.  The cluster divides itself into small collections of nodes, called
+*neighborhoods*. Each node is responsible for sharing any data it receives with
+the other nodes in its neighborhood, as well as propagating the data on to a
+small set of nodes in other neighborhoods.  This way each node only has to
+communicate with a small number of nodes.
 
 During its slot, the leader node distributes blobs between the validator nodes
 in the first neighborhood (layer 0). Each validator shares its data within its
@@ -26,6 +26,14 @@ make up layer 0. These will automatically be the highest stake holders, allowing
 the heaviest votes to come back to the leader first. Layer-0 and lower-layer
 nodes use the same logic to find their neighbors and next layer peers.
 
+To reduce the possibility of attack vectors, each blob is transmitted over a
+random tree of neighborhoods.  Each node uses the same set of nodes representing
+the cluster.  A random tree is generated from the set for each blob using
+randomness derived from the blob itself.  Since the random seed is not known in
+advance, attacks that try to eclipse neighborhoods from certain leaders or
+blocks become very difficult, and should require almost complete control of the
+stake in the cluster.
+
 ## Layer and Neighborhood Structure
 
 The current leader makes its initial broadcasts to at most `DATA_PLANE_FANOUT`