 We would go into a little more detail on the resource and Admission Control functions because this is something that is critical to the overall successful execution of the NGN with regards to different services. First we have to understand that resource and Admission Control functions provide some kind of abstraction and freedom from the underlying topology. That is if there is a topology which is meant for a certain kind of service, once abstraction is provided the same topology would be applicable to another kind of service. So this kind of abstraction helps the service control function to cooperate and work with the resource and Admission Control functions. It is important to mention here that although we have talked much about RACF, the resource and Admission Control functions, we have to understand that it is still not mandatory. NGN assumes that RACF can be done with or it can be avoided for best effort traffic because in best effort traffic the requirements are not very stringent in terms of Admission Control. Now we look at how the resource and Admission Control functions interact with the service control functions. The RACF or the resource and Admission Control functions interact with the service control functions with regards to how quality of service has to be enacted or it has to be implemented. For that the Admission Control is one of the most obvious activities that would take place. For instance for voice over IP which is based on let's say SIP kind of signaling mechanism if quality of service has to be implemented then in the presence of a large number of users some users have to be denied and some users have to be given priority over other users. So that kind of juggling or that kind of manipulation is an important function for the resource and Admission Control. Another important functionality that is required by the resource and Admission Control functions to be implemented is the network address and port translation because after all in a very dynamic environment where the user equipment is connected and is also mobile the IP addresses could be sometimes public sometimes it could be private and the private IP addresses keep on changing. So it means porting a private IP address onto a publicly visible IP address is a requirement that needs to be catered for using some kind of network address translation or we say NAT and the port address translation we call the PAT. We are not going to go into exactly how the NAT and PAT work but all we have to understand is that understanding exactly how the devices are connected to the network is an important functionality that should be implemented and should be communicated to the resource and Admission Control function because the service control function is just spelling out something that needs to be done that is what is to be done but exactly how it is to be done is the task that is that rests with RSEF. The RSEF now also interacts with the network attachment and control functions remember we when we talked about network attachment and control functions we were primarily talking about how a user equipment is attached to the network and how the services are used. Now if RSEF has to perform its tasks it has to exactly understand what user subscription is available for a certain user it certainly comes from the service access control functions but the service access control functions are after all implemented in the network element that is the user equipment the user equipment. So the user equipment once it interacts with the network element then the interaction between the resource admission and control functions and the network attachment and control functions becomes very obvious. Interestingly sometimes the resource admission and control functions of one kind of network have to interact with the resource admission and control functions of another kind of network it is to ensure operability interoperability number one number two the different service providers which provide the same service have to be governed by the same set of policies and rules and for that the resource admission control functions of one NGN have to interact with other NGN RSEFs because there could be multiple network operators and service providers.