 Let us continue with our understanding a little deeper about the protocols and interfaces. Now we are going to look at the most important functionality of mobile broadband networks that is mobility management. We'd see the role of DHCP and how the DHCP server is managed within the evolved packet core. What is the concept of anchoring at the gateway level and the concept of access at the gateway level. So our scope again here is the serving gateway, the packet gateway together. These can be implemented in a conjoined manner known as the system architecture evolution gateway. As you can see here it is now shown through a dotted block that contains two sub blocks as packet gateway and the serving gateway. So we'd look at the functionality with regards to the mobility management entity that we have earlier discussed. So mobility management essentially means managing IP addresses because each user equipment is supposed to have an IP address. Now since each IP address has two parts, mainly the network ID and the host ID. So if we are interested in changing the network from one network premises or jurisdiction to another because the user equipment is mobile. So the IP network is going to change correspondingly the network part as well as the host part is going to change. Of course there is provision both in version 4 of IP and IP version 6. Together the serving gateway and the packet gateway achieve this by defining the scope of their functionalities. DHCP or the dynamic host configuration protocol is of course essential in implementing the assignment leasing and rolling of the IP addresses for a certain administrative domain. So here for this particular scenario in the evolved packet core of the system architecture evolution, the packet gateway is responsible for IP address allocation. The DHCP server is either located next to the packet gateway or it is integrated within the packet gateway because essentially packet gateway is a server. Server is a software component so like a packet gateway software component the DHCP server could also be installed on to the same hardware system. Now the serving gateway in the presence of the DHCP server at the packet gateway acts more or less like a relay agent. So it means on behalf of the user equipments it forwards the DHCP requests and the replies from the packet gateway. So this results into the smooth and transparent assignment of IP addresses to the user equipment. So it means the user equipments may not necessarily be in one hop distance from the packet gateway. Now the packet gateway acts as a mobility anchoring point. This scope of mobility anchoring for the packet gateway is defined because now we are expecting the user or the mobile phone to be moving across the non 3GPP IP connectivity access networks as we discussed earlier like ITF and IEEE standards as well. Now the concept of mobility anchor gateway is something that we need to understand. Now as we just discussed in the last slide the anchoring point is where the user equipment actually can cross the traffic from one technology to the other technology. The gateway is something that sits at relatively higher level and provides interoperability in literal sense. So the packet gateway now acts as a mobility anchor gateway at a more local level. It means since it's a gateway so it means it is going to terminate the signaling which is related to IP version 6 especially for the proxy mobile IP version 6. Likewise this particular proxy mobile IP version 6 signaling is in the control plane. If we look at the data plane or the user plane the IP version 4 IP version 6 tunneling that is IP in IP which takes place at the user plane. The traffic is terminated at the packet gateway. So since the responsibility of the packet gateway is now elevated at a more anchoring gateway level so the home agent of the proxy mobile IP version 6 is also naturally located in packet gateway. A point that just relates to the scope of a packet gateway is since packet gateway is the most important element in achieving interoperability for 3GPP, LTE and non 3GPP radio access network technologies. So it has to provide the anchoring functionality, the gateway functionality and even the router functionality that we see here that is mobile access gateway. You can call it MAG. The MAG is again placed in packet gateway for proxy mobile IP version 6. This acts like an access router and you know access routers are connected to the core routers. The access routers are a bridge between the user equipment or the customer premises side and the core network. So as a mobile access gateway packet gateway now manages signaling which is related to mobility for the user equipment which is directly connected to the access links. The access link actually is a radio thing so that is why the protocol understanding of the radio has to be incorporated at the packet gateway. When we refer to the diagram shortly we will see what does it mean. So using the signaling the user equipment can be tracked in whatever ran or radio access network jurisdiction the user equipment is currently moving about in and then correspondingly it is used to signal mobility related information for the user equipment to the arriving or to the ran in which the user equipment is soon going to be entering. For non 3GPP IP connectivity access networks they have to implement the MAG functionality by emulating it. By emulation it means they have to make the functionality of MAG somehow possible either connecting to the packet gateway or at their own. Since we know for most of the traffic that enters from the user equipment towards the internet through the evolved packet core is sent through the serving gateway to the packet gateway and this is typically known as a home routed implementation. It means that the traffic is coming from the home towards the internet. Now in this case the serving gateway can actually implement the local mobility anchoring gateway and the mobility access gateway at its own. Let's refer to the diagram so that we can understand the role of different gateways collect in a complete diagram. Here you can see that whenever the user equipment has to send data through the packet switched interface to the evolved packet core it can opt from one of these technologies. As far as LTE, LTEA is concerned there's no problem because we have E node B home E node B and the like. However the scenarios that we have just discussed are actually referring to the non 3GPP user equipment such as IEEE and ITF compliant standards. Now you see there is an interface defined between the non 3GPP radio access network and the packet gateway. Likewise for the 2G networks we have the connection through the SGSN that is the serving gpr support node through the serving gateway to the packet gateway even through the mobility management entity to the packet gateway. So the point that we understand is that this packet gateway is now the highest level of gateway which is providing cross connectivity between these different technologies by acting as an anchoring gateway and as an access gateway. The serving gateway can provide certain level of anchoring however its scope is limited.