 When we looked at the services stratum, we saw two important entities, the service control function and the content delivery function. So understandably, these two are very much related to the how applications and services are provisioned. But the overall management, execution, configuration and essentially all the aspects related to the underlying network are contained in the transport stratum. So the transport stratum, if you recall, had two parts, the transport control and the transport functions and the transport control functions. Now the transport control functions are very very important and it is like the main engine or the centerpiece of the overall engine architecture. So in this module, we should look at how the control architecture and protocols are implemented. Now this module is an opening to couple of modules that we shall soon be seeing, inshallah. So we shall see the architecture first and then we shall look at the network access and control functions in respective detail in some of the modules that follow. So the network access and control function has a central position in the overall engine architecture. It interacts with the applications, the customer, the services stratum, the transport stratum including the radio, the resource and admission control function, the mobility management control function. Let's look at this figure once again. Here we see that the transport stratum has the transport functions and the transport control functions. The transport control functions has the resource and admission control, mobility management and the network and access control functions. Now the network and access control functions, let's zoom in into the network and access control functions. Here we can see that it has a couple of modules. These modules can be seen one by one. We are going to start with the access management functional entity and then we'll go into subsequently more detail. So the network access configuration functional entity is the network access and control configuration functional entity is the first one to begin with. What it is responsible for? Number one, since NGN is based essentially on the IP address, so it is responsible for the allocation of IP address, both in terms of the client IP address and the server IP addresses. The server IP addresses could be related to the DNS server and the other proxing servers which are used in for instance signaling for voice over IP like SIP servers. In IP multimedia subsystem. So DHCP, the dynamic host configuration protocol is a natural mechanism to allocate the IP addresses. Now these IP addresses could be assigned in a permanent manner. It's also known as the home address or it could be a temporary IP address known as the care of IP address. Now these addresses are related to something called the mobile IP, which when the right time comes, we are going to look at it. Mobile IP is responsible for provisioning mobility and maintaining the end to end socket intact. So the responsibility of the network access configuration functional entity is to make sure that the IP addresses are allocated and they are properly utilized to ensure that the connection is not compromised. So the binding or the association between these two addresses is also the responsibility which is implemented by the network access configuration functional entity.