Meghadoot

- A Hybrid Wireless architecture

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Control Zone Operation

For any MN to be a part of the CZ, the MN has to register itself with the IN. This involves three protocol messages - AP Beacon, Registration Request, and Registration Acknowledgement.

An IN periodically broadcasts the AP Beacon with the hopLimit field set to the CZ radius. The MNs that receive the beacon rebroadcast it to their neighbours after decrementing the hopLimit field. Thus, the AP Beacon packet is flooded all through the control zone. The MNs that receive the AP Beacon with hopLimit field as , mark themselves as gateway nodes and do not rebroadcast the packet.

The AP Beacon serves two purposes:

• IN Advertisement: The MNs get to know the presence of INs. It is possible that MNs receive beacons from multiple INs. In this case, they choose the best possible IN. Currently, the IN which is nearest(least number of hops) is selected. Other metrics can be plugged in.
• Next Hop to IN: The MN gets to know the node through which IN can be reached. This is required to send control packets for registration requests, route requests, and neighbour updates to the IN.