If an IN receives a packet on the backbone network, then it can either be from the Internet or from another Meghadoot network. There are two possibilities here:
An IP Packet from Outside: We can receive an IP packet either from the Internet or from another Meghadoot network with the destination registered with the IN as HA. If a packet is received from the Internet, the IN checks if the destination is actually present in its CZ. If so, it inserts the Meghadoot header (with source route to the destination) into the packet and forwards it to the next hop in the source route. In the event of the destination having moved to another IN, the packet is tunneled to the FA of the MN (destination).
Tunneled Packet from another IN: It is possible that an MN has another IN as the HA and is currently registered with this IN as a foreign node (Figure 3.3). In this case all packets destined to the foreign MN are tunneled from the HA to the FA. The present IN (which is the FA) untunnels the packet, inserts the Meghadoot header (with source route) and forwards it based on the source route.