handshake and inventory diagrams

ch06.asciidoc

@@ -67,6 +67,10 @@ To connect to a known peer, nodes establish a TCP connection, usually to port 83
 
 The peer node responds with +verack+ to acknowledge and establish a connection, and optionally sends its own +version+ message if it wishes to reciprocate the connection and connect back as a peer. 
 
+[[network_handshake]]
+.The initial handshake between peers
+image::images/NetworkHandshake.png["NetworkHandshake"]
+
 How does a new node find peers? While there are no special nodes in bitcoin, there are some long running stable nodes that are listed in the client as _seed nodes_. While a new node does not have to connect with the seed nodes, it can use them to quickly discover other nodes in the network. In the Bitcoin Core client, the option to use the seed nodes is controlled by the option switch +-dnsseed+, which is set to 1, to use the seed nodes, by default. Alternatively, a bootstrapping node that knows nothing of the network must be given the IP address of at least one bitcoin node after which it can establish connections through further introductions. The command line argument +-seednode+ can be used to connect to one node just for introductions, using it as a DNS seed. After the initial seed node is used to form introductions, the client will disconnect from it and use the newly discovered peers. 
 
 Once one or more connections is established, the new node will send an +addr+ message containing its own IP address, to its neighbors. The neighbors will in turn forward the +addr+ message to their neighbors, ensuring that the newly connected node becomes well known and better connected. Additionally, the newly connected node can send +getaddr+ to the neighbors asking them to return a list of IP addresses of other peers. That way, a node can find peers to connect to and advertise its existence on the network for other nodes to find it. On a node running the Bitcoin Core client, you can list the peer connections with the command +getpeerinfo+:
@@ -137,6 +141,10 @@ Let's assume for example that a node only has the genesis block. It will then re
 
 This process of comparing the local blockchain with the peers and retrieving any missing blocks happens any time a node goes offline for any period of time. Whether a node has been offline for a few minutes and is missing a few blocks, or a month and is missing a few thousand blocks, it starts by sending +getblocks+, gets an +inv+ response and starts downloading the missing blocks. 
 
+[[inventory_synchronization]]
+.Node synchronizing the blockchain by retrieving blocks from a peer
+image::images/InventorySynchronization.png["InventorySynchronization"]
+
 === Simple Payment Verification Nodes
 
 === Bloom Filters