In addition to providing all the functionality of an MN, an IN performs the additional task of maintaining network topology and provides quite a few services to the MNs. Hence, in addition to all the MN data structures (except APTable entries and registration information), an IN has some additional data structures, which are discussed below.
Node Information: An IN maintains information about every node that is either directly registered with it, or is currently registered with another IN as a foreign node, with this IN as the HA. This information is stored in a list. Each of these elements has a timeout value, which is refreshed either on the receipt of an NU Packet (if the MN is in the IN's CZ) or on the receipt of a Home Agent Registration Request from the FA (if the MN has moved to the CZ of another IN). If the timer belonging to an entry in this list fires, that particular entry is deleted from the list. Moreover, that node is also deleted from the link graph maintained at the IN. The node is now considered to be unregistered. For each MN, information regarding its HA, FA and type (Section 3.2.2 explains the various values type can take) are maintained.
Kernel Timers: Since an IN does not send MN Beacons it does not require a timer for that purpose. However, an IN does need a timer to periodically broadcast the AP Beacon.