 The mobility management architecture can be seen as having two parts, it has the transport stratum mobility management aspect and it has the service stratum mobility management architecture. So, we are going to start with the transport stratum because if you recall the next generation network architecture the service stratum is above the transport stratum. It means the physical connectivity and communication takes place as a transport function in transport stratum. So, we look at some of the important functional elements and procedures here. The transport stratum mobility management module actually takes care of the device mobility through mobility management control function. Mobility management control function is a service within the next generation network architecture transport stratum that handles IP based mobility management. It means the assignment revocation reassignment of IP addressing takes place here at the transport stratum. The scope of mobility management control function is to provide the continuity of service at the transport stratum. It does not involve QoS provisioning and continuity. It means when a user equipment has a certain quality of service being provided to it in one network, when it changes the network the quality of service may continue to be the same or it may degrade. If it degrades then the mobility management control function does not handle that. To handle it, the service stratum has to do something. At the transport stratum, the mobility is managed either through host involvement known as the host based mobility management or the network based mobility management. In simple terms, when a mobile or a user equipment itself is involved explicitly in managing mobility, it is known as host based and when it is aloof or it is agnostic to the change of location, it is known as network based mobility management. Each of these has its own pros and cons. The procedure in simple terms for mobility management is that the user equipment registers itself with the mobility management control function. Since mobility management control function is a module or a service in the NGN architecture, so depending upon the location and the way the mobility management control function is deployed, there could be a possibility that more than one mobility management control functions are provided in networks. So in that case, the user equipment might be leaving the jurisdiction of one mobility management control function and entering into the jurisdiction of another mobility management control function. For that, the signaling is performed. Signaling actually helps to identify and locate the user equipment geographical and logical location. In other words, the location management is performed through mobility management control function. If the user equipment in itself interacts with the mobility management control function module, it is known as the host based mobility management. And if the user equipment is not involved and two MMCFs interact with each other through signaling, then it is network based mobility management. It is simply described as a model with both these options here. You see that we have two MMCFs, each having its own location management and handover management functions. The only distinction between the two sub modules of MMCFR that location management actually helps discover the location. But the handoff, that means the process of leaving network and joining another network is carried out by the handover management function. So you see that the MMCFs can talk to each other, perform the mobility management signaling through signaling as such involving network based mobility. And when the user equipment interacts with the MMCF, it is host based mobility. The main functional elements of the mobility management architecture in the transport stratum comprising the mobility management control function are the mobile location management and the handover control function functional elements. The mobile location management functional element simply is to discover the location in terms of the network which is deployed. For instance, if it is a GSM as we had discussed, it would be in terms of location area code or LAC. For GPRS and UMTS, since it involves packet transmission, so we call it as the routing areas and LTE terms it as a tracking area. Luminology varying, but the concept remains the same that the IDs of the current network elements are returned. In terms of handover control functions, the simple job of handover is to ensure the continuity of the established sessions if permanence is a requirement. If permanence is not a requirement, then it's a much simpler issue. The service is disrupted from the leaving network and is reprovisioned in the joining network. This is exactly what we have seen. Mobility management control function is actually connected to the user equipment providing the location management and handover control services. The other elements, if you recall, the network attachment control function and the resource and admission control function have different responsibilities. We've already discussed them in detail while we were studying the NGN functional architecture. The location management, again, can be categorized to be comprising sub-functions. Although it seems quite obvious that location management means finding or identifying the location. But at the more specific level, it is implemented through certain routines or methods that is registration of the current location. It means when a user equipment is present in one proximity or one geographical area, then the current location of mobile is registered with the network. And when a user moves, the location is updated. So if the user equipment in itself is not actively involved in communication, so for a call which is terminating on the user equipment that is the user equipment is being interrogated. So the mobile or the user equipment is looked for or searched for. This process is known as paging. Once it is paged successfully, it is discovered to be existing at a certain geographical location with a certain logical identifier that is an IP addressing of that network. Then the connection is established and packets are delivered.