AP Table: This structure contains a list of INs (each is stored as an APTableEntry) from which the MN has received an AP Beacon. Each of these entries has a timer which refreshes on the receipt of an AP Beacon packet from that respective IN.
Registration Information: This structure stores the registration status of an MN. In the event of an MN being registered, this structure contains a pointer to the the APTableEntry of the associated IN.
Path Cache: This is the first level route cache, wherein complete source route is stored in each entry. Each of these entries times out after a fixed time4.2. This timeout value is refreshed every time the route is used.
Link Graph: This is the second level route cache, which stores the topology information as seen by the MN. The cache is a two dimensional array, in which each element indicates the current status of the link between those two nodes and varies between 0 and MAX_LINK_VALUE (0 indicates that there is no direct wireless connection). This link value is periodically decremented. This is achieved by having a timer in this link graph structure. Once the timer fires, it is again set to a new value. This ensures that the timer fires periodically.
Route Request List: Every route request that is sent is added to a list4.3 with a timeout value. This entry is deleted on the receipt of a route reply. If the route request times out, it is retransmitted. This is done for a fixed number of times, after which the route request entry is deleted.
Registration Request Entry: This structure contains information about a registration request for which no acknowledgement has been received. It has a timeout value, after which is retransmitted. This is done for fixed number of times, after which the request is cleared.
Send Queue: All packets which do not have a route to their destination are queued up in send_q. Each of these packets has a timeout, after which it is deleted from the queue. On the receipt of a route reply, the send_q is scanned for packets with destination address same as the route reply's. Meghadoot header (including the source route) is added to all such packets, after which they are routed and transmitted appropriately.
Jitter Queue:AP Beacons are broadcast by the IN and they move like a ripple from the IN to the gateway nodes. Consider the case when two nearby nodes at radius receive the AP Beacon packet. If both of them immediately try to broadcast the packet, there will be a collision. To avoid this, the packet is transmitted after a small amount of time, which is randomly picked. To achieve this, a timer is added to the packet and it is queued. Once the timer fires, the packet is broadcast. Jittering is performed for all packets that are sent periodically or are broadcast: AP Beacons, Neighbour Update packets, and MN Beacons.
