 While understanding the overall aspects of the system architecture evolution, it is important to understand how various protocols have played the role in implementing the overall architecture. And these protocols work through various interfaces which are established between different endpoints. In the module that we are going to take now, and subsequently few other modules, we are going to look at the system architecture implementation and evolution through different protocols and various kinds of hardware and software interfaces. Let's start our discussion a little bit about what gateways are we most familiar with, which play the role in implementing the all IP environment into the evolved packet core. So as we understand so far, the most important interfaces that have played the role is the serving gateway and the packet data network gateway. So we are going to look at their roles which are implemented through various protocols and interfaces. The lines you see here either dotted or colored coming from different modules starting from the mobile terminals through the UTRAN and its variants to the evolved packet core and then to the external networks including the IP and non IP networks. These lines actually show the interactions between different network elements. So these lines are actually referring to different interface implementations. The evolved packet core consists of some very important gateways, the serving gateway and the packet gateway being the most important ones. They have their roles in the control plane as well as the user plane. We are going to emphasize their roles according to different protocols and functionalities. Some common denominators of these gateways are these gateways implement switching as well as routing. And these gateways implement the quality of service enforcement and the policy and charging rule function enforcement through the enforcement points. So it means the serving gateway and the packet data network gateway that we call in a summarized manner as packet gateway. These act as the policy enforcement points. The scope of the policy and QS enforcement actually varies significantly from the serving gateway to the packet gateway. Serving gateway is the first gateway that comes on the way from the user equipment towards the external network. That is why it acts more at the packet level. So we say that the serving gateway implements quality of service and the charging functionality at the packet level. The packet gateway which is the external or closer to internet gateway implements the quality of service and charging functionality at the service level. Now the charging functionality which is implemented at the packet gateway level is consolidated as a charging report. It means that the service is charged after the service is executed fully. While executing the service multiple packets could flow from the user equipment towards the packet gateway and vice versa. The serving gateway actually has interfaces with the 3GPP RANs, non-3GPP RANs such as the EUTRAN for LTE, for EUTRAN for 3G radio access networks, for 2G networks which provide data connectivity through the edge service known as GIRAN. So the serving gateway for all of these acts like an anchoring point. When we say anchor point it means it is with regards to mobility management. So whenever the traffic is going to be generated from one radio site and is going to enter into another radio site, the serving gateway is going to act as an anchor. So this anchor is now known as MAP for inter-3GPP services. And for non-3GPP since now we are involving protocols, specifications, radio standards which are related to the IP connectivity access networks which are non-3GPP. This could include the ITF and IEEE standard. The mobility anchor point is of relatively higher scope. So that is why the packet gateway is now going to serve as MAP.