The roaming between the heterogeneous networks gives rise to the need of a mobility management scheme. Mobility management which is an essential requirement for the provision of network at anytime and anywhere allows access to the network from different locations while maintaining uninterrupted service. Mobility management includes two tasks of handoff management and the user location management. Location management enables a network to discover the current position of the user equipment through registration and paging; while handoff management enables a network to maintain a connection as the mobile node moves from one point to the other either within a cell (Intracell) or between cells (Intercell), and may be performed in two ways: soft and hard.
In the next generation mobile networks, the accessibility can be achieved -through a set of personal devices which gave birth to three high-level mobility types; session, personal and service mobility. Moreover, ad hoc networks also gave birth to more mobility types in term of ad hoc mobility and mode mobility.
Terminal mobility allows a device to roam between different networks with differing technologies while continuing to be reachable for incoming requests and maintaining the existing session during movement across different geographical regions. Adaptive techniques like middleware will provide terminal mobility (Rao, K.R., Bojkovic, Z.S., and Milovanovic, D.A., 2009)
Personal mobility is a step ahead of terminal mobility in the sense that it is more of the user than device. It is aimed at providing a seamless personal to users without considering the device used by the users.
Session mobility allows continuous enjoyment of a session as the user roams from one device to another, and Service mobility allows users access to service even with changes in network providers.
“In allowing users to access any system at anytime and anywhere, the performance of mobility- enabled protocols is important. While Mobile IPv6 is generally used to support macro-mobility, integrating Mobile IPv6 with Session Initiation Protocol (SIP) to support IP traffic will lead to improved mobility performance.” (Nursimloo, D.S. and Chan, H.A., 2005).
Mobility Management consists of all operations required to serve a mobile terminal (users) with services while on the move. There are two types of mobility a network has to support in cellular networks: terminal and personal mobility. Terminal mobility refers to the situation in which a mobile terminal is offered the necessary services for establishing and maintaining access by the network while in personal mobility which is independent of the mobile terminal is a scenario in which the network must offer the necessary services for establishing and maintaining access between the mobile terminal and the user (Kupper, A.; 2005).
The operations of mobility management can be divided into two main subsets, namely: location management and handoff management. Location management is the process of discovering a mobile terminal (MT) to enable a network authenticates and updates the location for the establishment of connection. And this can be achieved through location registration (update) and paging. Handoff management on the other hand according to Rao, K.R.; Bojkovic, Z.S. and Milovanovic, D.A. (2009) is performed in three steps: initiation, connection generation, and data flow control. This can be either vertical handover (that is, across radio access technologies) or horizontal handover (within a radio access technology). Another way of classifying handoff management is to identify the operation domains which are: inter domain and intra domain handovers (Anderson, K.; 2012).
Rao, K.R.; Bojkovic, Z.S. and Milovanovic, D.A. (2009) further classify the mobility of a mobile terminal (MT) in a network into three broad categories: Micromobility (intrasubnet mobility); Macromobility (intersubnet mobility); and Global mobility (interdomain mobility).
In GSM and UMTS, mobility management takes place at the data link layer whereas in a heterogeneous wireless network there is a need for a mobility management at layers above the data-link layer in “order to take advantage of all available technologies at a certain moment and a certain place”(Anderson, K.; 2012: 32).

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