Minecraft wiki entry for Classic_server_protocol, associated text: 1 Minecraft.net Communication
1.1 Heartbeats
1.2 User Authentication
2 Packet Protocol
2.1 Protocol Data Types
2.2 Client → Server packets
2.3 Server → Client packets
3 Player Position
3.1 Fixed Point
3.2 Standing On Things
3.3 Orientation
4 Color codes