Three steps are involved in accessing and using mobile data networks. These steps are necessary for mobility management and are analogous to the phases of a connection-oriented protocol. The details of each step depend largely on whether the system uses a tracking or searching mobility management strategy as described in Section 1.4.1.
At some point, the mobile host must announce itself to the system ("here I am!") before it can receive services. This announcement or registration serves several purposes, including establishment of a SubNet Point of Attachment or SNPA (i.e., the local address where the mobile can be accessed), obtaining network connectivity via the local mobility-supporting router, authentication of its identity, authorization for use, encryption key exchange, link layer parameter negotiation, etc. The mobile registers to a single mobility area at a time.
If the system employs a tracking-based mobility management strategy, the mobile will register once and thereafter remain virtually connected to the system, even if it neither sends nor receives data. If the system employs a search-based mobility management strategy, the mobile will register each time it wants to transmit data, or in response to a system page (because another entity wants to send it data).
Registration includes but is not limited to mobile network access. After performing the actions necessary to access the mobile network, the mobile host must then initiate the mobility management process.
Once the mobile host has registered to the system, it may use the resources of the system to access the rest of the world. At this point, the mobile host must behave and serve its applications much the same as a conventional host. Mobile network usage could last a long time or for only the duration of a brief data communication. During this interval, the mobile host is accessed (i.e., data packets are sent to it) via the mobility router to which it is registered.
Following its use of the system, the mobile host leaves its subnet point of attachment. The de-registration serves the purpose of freeing-up network resources (such as identifiers, memory blocks, routing table entries, etc.) that would otherwise be allocated to a quiescent mobile. A mobile host might deregister because it no longer requires mobile access or because it has moved out of the mobility area to which it was registered.