 The role of RSEF in the service stratum and the transport stratum for SCF and TF is realized to certain functional entities that we would be discussing in this module and then we look at an overarching view on the operation of RSEF through these functional elements. So the first one is basically the policy decision functional entity it actually means the policy which is going to be implemented for resource allocation and if a certain flow has to be admitted or not. So since we are now talking about the RSEF which is in the transport stratum so we want to have interaction with the service stratum for SCF so it means that PDFP is going to be the single point of contact with SCF this helps the complexity of the transport stratum to be invisible to the service stratum and vice versa then we have the transport resource control functional entity. Now actually this is what supports the presence of heterogeneous technologies this provides a basic admission control decision to be implemented by the policy enforcement functional entity we are going to have a look at it just now. Now this transport resource control functional entity as the name implies has to control the resources at the transport layer so it is going to work independently of the service it means the service control function is going to talk to the PDFE and this PDFE is now going to talk to the TRCFE. This is exactly what we see here if you look at this diagram you see that we have the service stratum with SCF shown to you here only because that's the point of concern at the moment then we have the RSEF implemented primarily through the policy decision functional entity now this policy decision functional entity has a has a one-on-one mandatory link with SCF and certainly with policy enforcement as well but it also has certain optional connectivity with entities such as mobility management network attachment and the management or for performance management. Now these optional are we are going to have a look at these incidentally this PDFE also has a mandatory interaction or interface with the transport resource control functional entity because it is going to be this TRCFE that is going to provide the policies to be policy decisions which are going to be implemented finally by the TREFE that is the transport resource enforcement functional entity this is the last point where the policy is given to the lower technology to implement in terms of specific bandwidth allocation buffer allocation priority assignment traffic differentiation etc etc so let's start with PDFE now we already know that it has certain optional connections but it has a mandatory connection with the service control function the policy enforcement basically is is essentially a router or a gateway that takes instructions or decisions from the PDFE and enforces so we say that PEFE is actually the point where we are now going to look at the final realization of the resource and admission control since we are talking about providing a certain flow certain behavior for implementing QoS for that flow we are looking at the transition points where traffic enters from one network and goes to the other this can be between different networks at the same level or it can even be between the core and access networks now this traffic resource control functional entity basically is in the transport stratum that instructs the resource enforcement functional entity so resource enforcement actually is where something actually is passed to the technology as I had said before now since this TRCFE is service independent so it is in the middle but since it is talking to the PDFE now it is important to understand that tREFE is going to be technology dependent because we are going to expect multiple tREFEs for different technologies different protocols different vendors different service providers this is exactly what we have just discussed you see here that here this enforcement point tREFE has a mandatory field with the with the with the user equipment so it means that this is the last entity in terms of the NGN architecture that implements RSEF in true form so RSEF basically is going to use all these functional entities to realize QoS enforcement through resource allocation and admitting or not admitting so it involves the certain steps that is discovery and selection so what do we mean by discovery discovery is basically all the functional entities that we have discussed some of them are mandatory some of them are optional so we need to discover them now this discovery is based on certain information which is required either this information can be static for instance pre-assigned IP addresses or domain names or it can be dynamic for instance the current topology which exists for the resource and admission control function to implement and the current level of connectivity of all these entities selection is basically after having discovered these functional entities selection is basically depending upon the QoS requirements coming from the service control function certain entities are binded together or you can say they are they are related to each other now in that particular requirement scenario depending on what the QoS requirements have come from the service control function some of these parameters can be again not limited to the type of service which is expected from the underlying network the technologies and the protocols which are working and the service attributes in terms of QoS parameters and user preferences and the network condition etc