 The mechanics of quality of service are primarily the means through which quality of service can be ensured. So these are actually the actions or the functions which are implemented across the NGN. We'll start up with one of the most important quality of service functional implementations known as the admission control. We'd formally look at the definition, then we'd look at the requirement of admission control in IP networks and then in NGN. So admission control is basically the control of admitting a certain service flow, user, service type, device or even a whole network. So this is basically a technique which has been adopted from the traditional telecom network. In traditional telephony, a caller makes a call to the call party to the network. Now the network has to make sure that there is enough network resource available to establish a call between the calling party and the call party. We have examples, you know the SS7, the signaling standard 7, a whole framework that implements such signaling. Using this signaling, if the network realizes that it does not have enough resources, so the call can be denied. Or else, if enough resources are available, then the call can be established end to end. For instance, in a TDM network, the time slots have to be available end to end. If it is FDM network, then the frequency or a certain carrier has to be ensured for establishing the call. Now the concept of admission control is central to the real time services. It means traffic such as the voice over IP traffic, IP, TV, etc. These are real time services which demand the admission control as a functional module for QS provisioning. In typical IP based networks, intrinsically admission control is not needed because the services which are typical or inherent to the IP networks such as elastic services like browsing, email, etc. These are not very sensitive to latency. Consequently, admission control was not thought about as a serious concern for these IP based networks. Nonetheless, congestion control is a very important functionality which is implemented as a requirement in IP based networks. And as we very well know, the TCP is used for congestion control mechanism as an end to end mechanism. Not to discuss because it is not in the IP stack. ATM also has its own congestion control mechanism at the network layer and which is based on the network based congestion control. That's just beyond the scope. However, the most important point from this particular slide is that admission control is not a major concern in IP based networks. It is a concern in terms of congestion. And congestion is very well handled through TCP. For NGN, that has to cater for both these worlds that is services and applications coming from IP based networks and the emulation of real time services coming from PSTN, PLMN, the broadcast television. So admission control is needed for the emulation of traditional services which have the real time component. The best effort services are not needing admission control. So it means the admission control is not a requirement for provisioning these elastic services. But since admission control is going to be there in NGNs, these best effort services would now be influenced in terms of service availability and response time. Though it is not a concern, but these services are going to adapt now to admission control. So if the admission control gives priority to the real time traffic and services, the best effort services would be relegated to a lower level and the best effort service is going to adapt. But the best effort services are known to provide best effort service. So it is not going to have much impact on the service level agreement.