 Let's continue. Now we are going to look at some interesting deployment approaches. It means we are going to look at the scenarios in which mobility is managed under different protocols and interfaces. Let's look at how the mobility is handled. Mobility is basically the movement of the user equipment at will. So it is essentially uncontrolled mobility scenario. Since the environment is so heterogeneous, all the radio access network technologies connected to the system architecture evolution, including both 3GPP compliant protocols and standards and non-3GPP protocols and standards. So for such highly heterogeneous environment, the deployment can be either through mobile IP version 4 or dual stack mobile IP version 6. It means both IP version 4 and IP version 6 compatibility support is provided. Let's quickly have an overview of the interfaces which are defined in this 3GPP architecture for the next generation networks. We have the interfaces, we have the plane, either control or user plane and correspondingly we have the protocols. Some of these protocols are readily understandable by the students. For instance, stream control transmission protocol, IP protocol, user datagram protocol, the famous diameter protocol which is used for the triple A services, the remote dial-in user service for the triple A which is a predecessor to the diameter. Now let's look at the interfaces starting from S1 interface that is the interface between an E-Node B that is a base station defined in the 3GPP architecture for LTEA, LTE and LTEA and the mobility management entity. Now this is with regards to the control plane. Then for the user plane, we have the S1 interface defined again between the E-Node B and the serving gateway for the user plane because mobility management entity does not carry user traffic. Then we have S5-S8 interface, this is of interest, we are going to look at it. Then we have S6-B interface, we are going to look at it. The GXC interface, we are going to have a reference of it. Then we have some interesting interfaces like S2-A interface, S2-A interface comes in lots of flavors that is S2-A for the packet gateway and the trusted IP, trusted means that there is some kind of authentication which is already there between the connectivity access networks and the packet gateway. So S2-A as a user plane is defined for the proxy mobile IP version 6, then S2-A for the trusted IP cans at the control plane, S2-A for IP version 4 only, user and control. So you see that these interfaces come in variants because each variant is supposed to achieve compatibility for certain pair of gateways and network elements. Then we have S2-Bs, again S2-Bs are worth our interest as well and then S2-Cs both in the control and the user planes. As we discussed for implementing mobile IP version 4 scenario, S2-A and S2-B interfaces are defined. In this case, in fact we have already described it, the packet gateway contains the home agent. The likewise the trusted or untrusted IP cans contain their foreign agents because the user equipment moves within these IP cans. Now the user plane or the data plane is actually based on tunneling that is IP in IP. As far as non-3GPP IP cans are concerned the user equipment can actually implement dual stack mobile IP version 6 that is both IP version 4 and IP version 6 clients can be supported. This is known as the DSM IPv6. Again in this case the home agent resides at the packet gateway. Now the scenario that we have discussed here is although mentioned under the heading of non-3GPP IP connectivity access networks but it is equally applicable to 3GPP as well because the position and the placement of the home agent and the foreign agent are going to be at their respective places. The S2C interface is interesting because it is between the user equipment and the packet gateways. You see it's a direct interface and just for the sake of discussion we will see the S2C interface both from the control and data plane perspective how and using what protocols it implements the functionality. Then we have S5 and S8 interface. The S5 interface actually is activated between the serving gateway and the packet gateway as long as the network remains the same but S8 interface is there once the serving gateway in the visited network and the packet gateway in the home network are different. So let's get go back to the description of protocols which are used in these interfaces as we had just said S2C, S5 and S8. So you see S2C user plane the second last line is using IPv4 version 6 over tunneling within IP. So this is IP in IP user plane. As far as the control plane is concerned it is using dual stack mobile IP and again it is encapsulated within IP version 4 or IP version 6. The S5 and S8 interfaces either in the control plane or in the user plane are using protocols that we shall soon see. This is the GPRS tunneling protocol for the control plane GTPC, GTPU and it is using it along with UDP and IP. It means GTP is an application layer protocol which is encapsulated within UDP datagram which in turn is encapsulated in an IP datagram. So we see that both for interface S5 and S8 the user and control plane is using the same protocols.