 Now, we are going to look at the functional architecture of NGN that implements resource and admission control. The RSEF or resource and admission control functions are basically a suite of services offered through certain functional elements. So, we look at the need of RSEF in fact, we are somewhat familiar with it once we looked at the NGN functional architecture, we did look at it but now we are going to go a little deeper into it and then we are going to look at the requirements from the ITUT for implementing RSEF in order to provide certain services to the users. So, RSEF is basically somewhat kind of an arbitrator or an intermediary between the service stratum and the transport stratum. So, it means it interacts with the service control functions and the transport functions. The RSEF gets invoked I mean it gets activated to implement policy decisions on the basis of certain criteria. These criteria are definitely related to the entertaining or handling of user request to get a certain service. This is going to be based on a variety of factors for instance the service level agreement, the rules which are defined by the network for policy then what type of quality of service classes are there and is the network able to implement QoS differentiation. An example can be of for example, there are certain priorities which are given to voice, video, interactive and certainly best effort. So is this network that we are considering with RSEF service or module in it going to offer priorities for all these kinds of traffic and is it going to give the priority to some over the other as like the highest priority. Now, this is again a very important consideration then the network related information which is the quality of network while a network commits certain quality of service to a user then the quality of network at that run time in terms of the buffer occupancy, the channel impairments, the link losses etc. are very important. So, in all we can say that the link status and the average utilization of the network infrastructure again plays an instrumental role in helping the RSEF take certain decisions. Now the ITUT actually has come up with some functional requirements to be catered for or met through RSEF. These are very obvious but we need to go through each one of them and if there is a requirement we can deliberate on any. The first one is the control of QS related functions in transport stratum likewise RSEF is also going to handle the QS related functions in the transport in the service stratum support for different types of access and core transport technologies very important because RSEF has to be aware of the type of network it is connecting to the technology features which are available through which QS has to be provided. And then support for a variety of customer equipment now this customer equipment is something that is a user's choice it means while not bothering the user to take on with a certain type of device RSEF has to make sure that the underlying network infrastructure complexity remains hidden from the user and still the service is offered in the best possible manner. We already know the arbitration then there is a need for RSEF to support different kinds of QS provisioning for instance absolute QS control that is strict QS control loose QS control known as the relative QS control differentiation of different QS parameters including the bandwidth requirement the buffer allocation link loss permissibility prioritization etc and then QS signalling has to also be incorporated into RSEF because it is very important to make sure that the signalling traffic is not compromised in any manner so QS for signalling has to be there as well then the most important job for which these companies actually work is the money matter so the policy and charging control functions also have to be in sync and in coordination with the RSEF likewise RSEF is expected to provide support for unicast multicast traffic usually broadcasting is something that is so heavy it has a toll on the network to an extent that QS becomes a non-issue the delivery of traffic to the users becomes the primary concern but broadcasting is something which is very seldom done so mostly the unicasting and multicasting are the concerns for RSEF then if there are multiple operators and each operator has its own service level agreement then the inter provider service level agreement mapping has to be done for multiple networks coexisting together for different times of services for instance there could be real time IPTV or there could be time shifted TV now what exactly is going to be the shift when I say time shifted it means that it is not live it is going to have some delay but the understanding of delay in one engine implementation by a service provider may be different from the other so the RSEF has to take that into consideration as well then when mobility comes into play RSEF has to interact with the mobility management functional entity which is again very important and then QS adaptation that we've already discussed either downgrading or keeping the QS consistent across different engines operating together