 The importance of network performance measurement cannot be overstated, because it is something which is related to ensuring that a certain quality of service is provided to the users who are the customers or the subscribers of a certain network provider and a certain service provider. NGN looks at it very critically and there are certain network elements and functional entities which together work to implement the performance measurements. The management of performance measurement is a very crucial aspect that needs to be understood in detail from the perspective of NGNs. So we'd look at what are the service delivery scopes, because these scopes are going to determine the complexity of performance measurement and managing it. Then we'd look at the network elements partitioned in the form of segments and we'd look at the overall management model. It is now obvious that performance measurement in NGNs is very crucial to provide quality of service based services to the end users. In terms of the functional entities which are required to perform these measurements, there is NGN recommendation that comprises three functional entities. Starting from the bottom, going to the top in the form of a hierarchical tree, there is a functional entity known as the performance measurement execution functional entity. It means this is the functional entity that actually implements the performance measurement. Then we have the whatever measurements are made are sent to some kind of processing server. It is again another functional entity. So it is the performance measurement processing functional entity. So whatever is processed and the conclusions made are shared with the network administrators and with the policy makers through a functional entity which is hierarchically at the top. This is the performance measurement reporting functional entity. So we can think about the root node as PMR. Then we have multiple PMPs and then we have the PMEs at the leaf nodes. The management of performance measurement is something that has to be dealt with very wisely because it is going to have a toll on the overall network traffic. Usually the network traffic is dedicated or it is normally assumed to be solely for the end users. But from the operational management viewpoint, these measurements are going to have their own toll. So some kind of a wise organization and management for these measurements is essential. So what the NGN community does is they actually have thought about segmenting or partitioning the end to end network between two user terminal equipments in the form of network segments. Each segment can be assigned to an independent administrative authority, a different network manager who is responsible for maintaining quality of service. This quality of service provisioning through the performance measurement is now in the context of basically getting the active logs of the network. So in order to do that, the live performance is measured through some kind of query or probing mechanism. So active probe is initiated and then live measurements are made and after this process is done to the satisfaction, then this probe is terminated. So this sending out probes and receiving the responses to these probes has an overhead. Sometimes in certain situations for certain users and certain traffic types, this kind of interventional probing is not recommended. In that case, some passive measurements can be used. Passive measurements are actually non-invasive and the traffic which is users traffic is logged in terms of their headers and the active routing tables are logged and copied for subsequent usage by the functional entities that we have already seen. So correspondingly, when we look at the performance measurements, these performance measurements would have their scope corresponding to the scope of the service for which we are interested in collecting these measurements. So the services can be thought to be delivered to a certain scope. Now the innermost scope is basically edge-to-edge and the outermost or the end-to-end is the terminal equipment to terminal equipment. So the edge-to-edge service scope is where the services extend to the network provider's edge. In this case, the network provider edge is a gateway. So when the services are confined up to the gateways, it means that the network measurements would be correspondingly measuring the performance of the service provisioning only to this extent. Then we have site-to-site. Site-to-site actually means the site where the user is connecting to the network through the connectivity service network. So the customer premises network which is connecting to the connectivity service network is the scope for site-to-site. For the terminal equipment to terminal equipment, the services actually extend from the customer premises network to the customer equipment. In that case, if we are looking at the service delivery from TE to TE, in other words, we are looking at the end-to-end scenario. That includes site-to-site and edge-to-edge. So it reflects the aggregated performance of all these segments combined. Let's look at the seemingly complex but very insightful illustration of the overall model for performance measurement. Here we see that we have the customer premises network at the bottom. We have CP&A on the left-hand side, CP&B. Then we have customer premises network connecting to the access network through the edge. It is known as the connectivity service network. The access network is then connected to the core network through its own gateway. Then we have the transit network or the intermediate network that can connect multiple cores. So we can actually think about we are going to have customer premises network for sure. We would have one or more access networks. We could have one or more core networks. We could have zero or more transit networks. Now if you continue looking at here, you would notice that the scope of service delivery is shown here as well. For instance, we have the TE to TE scope, which is the end-to-end scope. Then we have the site-to-site scope that is you can see here we have edge-to-edge. And then we have the last one that we can see the overall transit segment. So we have multiple scopes. You can see here that these scopes correspond to the connectivity between the terminal equipment and the networks which provide service to it in order to reach the other terminal equipment. You can see here there is something interesting you see here known as demarcation point. So we will talk about demarcation point, what is it and how it can be used as a reference point where these measurements can be made. The segments actually are nothing but the portions of the end-to-end network which is split into tangible and administratively provisionable networks, subnets. So we can say that segments in NGN actually include all the access technologies including DSL, Ethernet, SDH, PDH, these lines, whatever. These segments actually could be the ingress or egress access core transit etc. Now you can actually see I didn't comment on it back then but when we have the calling party and the call party. From the calling party perspective we are talking about the egress where the request is being sent out and the calling party is where the traffic is coming in so it is the ingress segment. So what are these demarcation points? A demarcation as the name implies is to identify or label or earmark something. These are basically the points which are the network elements which are located on the edge of the connectivity of different networks. For instance if we have an edge node in the access network which is connecting this access network to the core then this particular device, a network element like a switch or a router is going to be the demarcation point. The demarcation point is place where the measurement can be made. So usually the demarcation points are measured in pairs. So we have the ingress demarcation point and we have the egress demarcation point and we look at the scope of service from the point of view of the ingress and egress demarcation point according to the scope.