Just like almost every other network out there, this network is split up into two logical concepts, LAN and WAN. This is the document in which they are described.
The LAN is a Local Area Network. In this network, each site has it's own LAN that is identical to all of the other sites. How convenient is that?
Details on the LAN design are here in the LAN folder.
The WAN is a Wide Area Network. This is the network that connects all of the LANs together.
Details on the WAN design are here in the WAN folder.