 Let's look at the mobility management conceptual framework from another perspective, similar to the variety of mobility in terms of the network attachment point. We can look at mobility as engine IDs or the identifiers. It is a very important concern because the variety of identifiers actually necessitates a mechanism that can switch the ID of a user equipment when it is moving. Depending upon the last network to which it was connected and to the new network to which it joins, the IDs have to be correspondingly assigned. We will start with the general understanding of the need for identifiers. The addressing of process, user, equipment, service, network, network access point demands that we need to have proper addresses that can be defined down to the granular levels. It can be understood to be a serious concern when mobility is also at play because we don't have static services. We have users on the go seeking service continuity, maybe changing service. So we have lots of services. The user equipment is connecting, disconnecting, again connecting, disconnecting while moving. The communication modes are changing and the devices can change because a user is logged on into the network service using one device, then it changes the device. And the physical or the geographical position in itself is changing. So it means that the need to have identifier as a mobility management requirement is beyond doubt very critical. Broadly speaking, we can think about the user IDs changing or the location IDs changing. Let's start with the user IDs first. Each user or its device has a unique identifier, of course. The user ID can be of any type depending upon what kind of network or technology is integrated into the overall next generation network architecture. For instance, for GSM, we have MC, the International Mobile Subscriber Identification. We have the E.164 numbering that translates a hierarchical domain like numbering scheme for PSTNs. Then we have the User Uniform Resource Identifier used in SIP for IP Multimedia Subsystem Based Services. We have email IDs and the list can go on. So it means these user identifiers have to be managed. If a user footprint moves, then correspondingly, the user identifiers have to be ensured for continuity of service from one network to the other. A very major concern, in fact, a bigger concern is to know the location through its own ID. The location information is managed through location management module, which is not a single module in itself, but it comprises certain other functional elements. The location management actually determines the current location of the user so that all the calls which are terminating for the user or the ongoing sessions are not disrupted. The location information can be categorized as the physical location, the geographical location, through a physical identifier. The physical identifier is a well-known concept. We know that in Wi-Fi IEEE 802.11, we have the service ID of the access point to which the laptops and other wireless devices connect. We have the base station ID in cellular networks. Each base station ID is associated with a location area code. Then we have the logical ID. Physical ID is more at the device level. Logical ID is something that can be translated into a device and it can then be changed to another device location. So the logical location ID actually is nothing but an IP address. So it means an IP address which is assigned to a certain access point or a base station can be unassigned and can be reassigned to another access point or to another base station. So these IP addresses are used to realize routing. So a routable IP address is basically the best representation of the logical location of a certain network element. So the mobility management for the next generation networks primarily focuses on the logical location identifier. Obviously the network ID or the network part of the IP address actually determines the network to which the user is currently connected at the moment. These identifiers, the logical IDs for the location like simply IP address assignment is either temporary or it is permanent. So we say that these IP addresses can be assigned temporarily when a user moves from one location to the other. Depending upon the user movement, a user can be assigned an IP address when a user moves to another location and it is assigned a new IP address. This can happen for the network devices as well that is a certain ISP buys a pool of IP addresses and assigns addresses to its network elements. But then the pool of IP addresses is changed. New IP addresses are assigned to the network elements. So anyways, the concept of being temporary is well understood. In the case of persistent IP address assignment, the IP address does not change. It means the persistence can be in terms of time like days, months, years, maybe, or it can be in terms of the continuity of session. So as long as the session is alive, the IP address does not change. The protocol from the ITF, the mobile IP actually uses both these terms like the home address which is given by the home agent to a certain user equipment is permanent. It does not change. When a user moves to another network, care of address is assigned to it by the foreign agent. So you see a mobile IP is a classical mechanism that implements both temporary IP address and permanent IP address together to provide seamless continuity of sessions. This is the overall representation of the identifiers used for managing mobility. User IDs are quite obvious. The location ID can be represented as persistent location ID or temporary location ID.