 Now, we are going to look at an interesting end-to-end scenario through an example of IPTV where the resource and admission control function carries out the admission control by taking the help and implementation of its own functional elements. We start with the requirements of IPTV and then we look at the operation in detail. The IPTV admission control is different from voice over IP because voice over IP is symmetric and it is between two live audience. In IPTV, it could be streaming content that is live streaming or it could be stored content and it is usually simplex. So we understand that NGN has different service requirements. NGH has its own different admission control. So if IPTV service has to be demonstrated through an example, so let's look at a situation where we have an inviter and we have an invitee that is two friends, a friend who wants his other friend to watch a content and the friend is not going to pay rather the invitee is going, the inviter is going to pay. So we look at the scenario where a friend A invites friend B, friend A is the inviter, friend B is the invitee and friend A is going to pay for the service. So we say that user invites one of his friends to watch a TV program and is willing to pay for it. If you look at the end to end scenario first diagrammatically and then we are going to go into the details, we are looking at the process that starts from the application layer. So the application layer gives its own QS requirements to the service control function. The service control function initiates the service or invokes the service by taking the invitee into confidence by sending it a request to allocate its resources. So the resource initiation request is sent to the PDFE of the invitee and then the policy decision is made and then the resource initiation request is made to the transport resource control which responds to this initiation request because if the underlying technology is not supporting then this end to end scenario cannot be realized. Then the admission decision is made, that is it is finally decided that the admission shall be made. So after that the policy decision functional entity has to enforce the policy. So now it sends a resource initiation request to reserve the resources and then it gets a response from the policy enforcement functional entity. Once it has finally gotten the response then the resource initiation response is sent to the SCF. Now this is the overall or the end to end scenario. We are going to look at the further details which are involved at every step. So after the invitee accepts the invitation from the invitee, the service control function sends a request to the invitee's RSCF. Now all these PDFE and this the transport resource function functional entity, TRF, FE are part of the RSCF. So whatever is happening is happening within the RSCF. The bill is going to be charged to the inviting party that is the invitee or friend A. So the RSCF does not need to check the subscriber information of the invitee because even if the invitee does not have zero credit, does not have any credit or it has zero credit so there's no requirement as such to charge it. Now the RSCF through its own PDFE makes a policy decision by referring to the policy rules if this provision is allowed for a friend to invite another friend and upon authorization it allocates the bandwidth and the QS class so it means it identifies what bandwidth is required and to which QS class does this IPTV stream belong to. Then the invitee's network PDFE is approached by the RSCF of the invitee's network to check the resource availability with the transport resource control functional entity of the invitee's network. So once the resources are found to be ample then a final decision is made. There are two possibilities if there are enough resources or if there aren't enough resources. If there aren't enough resources the media flow shall not be entertained and this IPTV service shall not be offered or it won't realize for the invitee. So in that case the PDFE sends initiation response with a rejection and also provides a rejection reason in terms of which resources are short and then this whole process is going to terminate but if there are enough resources then the PDFE sends resource initiation request to the policy enforcement functional entity to install the admission decision. Underlying actually means taking the QS policy taking the bandwidth requirement and the QS the device or underlying access technology shall now be configured to carry out this media flow transmission. Now the policy enforcement functional entity takes the final admission decision from PDFE and sends the resource initiation response to the PDFE that well whatever policy decision you made I have implemented it. Now the PDFE sends a response back to the initiator service control function that finally referring to the QS policy which I have I have admitted the resource for the media flow that you had requested. So in this whole process there is another entity which is going to carry out the charging process that is the if you recall the policy and charging resource function. So the application function which is at the top in the service stratum requests the service information from the PCRF the policy and charging resource function acquires the user profile from its database in this case it is going to be the Inviter or Friend A this can be the home subscriber station or the HLR home location register to make the policy decision. If the decision is positive then the PCRF is going to send policy specific policy which is applicable to Friend A's account and what rules are going to be implemented to the RSEF and then RSEF is going to translate it into whatever actions it has to tell to the policy decision functional entity and then policy decision functional entity talks to the policy enforcement functional entity for enforcement. So this is the final closure to the media flow that is now invoked and the invitee or Friend B is now enjoying the IPTV stream a television program and Friend A is paying for that.