 The importance of the process through which we have seen the LTE and LTEA networks evolving into today's shape is very important to be understood. In this module, we are going to look at the system architecture evolution as a process and as the underlying concept for the third generation partnership project. We'd see the concept of overlay networks and the advantages which come from the relatively flatter hierarchy in today's networks. So the overall architecture saw the migration from monolithic networks including both the bearer path and the signaling path to more overlay concept. Overlay actually means that on a physical network, multiple functional networks can be overlaid. So 3GPP mobile networks actually are based on two main overlay network architectures, primarily splitting the functionality of the user plane and the control plane. So the traffic of users is actually routed in a different way as the traffic used for control signaling. There are different network entities aka the gateways which perform these functionalities. The overall migration or the evolution from the originally monolithic design to the overlay based design actually also necessitated that the role of some network elements should be deprecated and there is a requirement now to have the role of multiple functions assigned to the network elements. So consequently, the hierarchical network topology started becoming more flat. If we look at the evolution that we have already investigated in the previous modules that the releases starting from release 99 to the release 6 up till release 7, the radio network controller was an essential part but then it was obviated or deprecated making the hierarchy relatively flatter. Let's look at the architecture in different forms over time. We see from the left most side we have the high speed packet architecture here starting from the base station or the node B to the internet including the network elements as the serving gpr support node and the gateway gpr support node. We have two dedicated overlays for the control traffic and for the user traffic. So this is straight away the hierarchical architecture. If you move from HSPA to the direct tunnel architecture which is the second block diagram from the left side we see we have the concept of direct tunnel. Direct tunneling actually meant that the radio network controller which is on the core side is now establishing direct connection with the gateway gpr support node instead of routing it through the serving gpr support node. So this actually meant bypassing SGSN for the bearer path. Moving on we see that the RNC in release 8 onwards was deprecated. You don't see it here and we just see SGSN and GGSN connected to node B and then we see in the system architecture evolution SGSN was subsumed into the evolved packet core and we have instead another entity known as the mobility management entity and we have the packet data network gateway. So as we just discussed the flatter hierarchy definitely came as a natural consequence and the first move definitely was having a direct tunnel in release 7. This system architecture evolution that we see with the mobility management entity is actually what defines today's network and the functionality of the system architecture evolution primarily resides into the core of the network. We will see the evolved packet core that functions in LTE and LTEA networks today. So we are going to continue with our understanding of this diagram and we will see the role of certain network elements becoming obvious in due course of time. So the most natural advantage of having this flattered architecture is number one it is simple and number two it allows the heterogeneity because now we don't have to worry about the specifics of each and every technology right down to the building blocks starting from the base station or the node B. So the simplified network architecture results into lesser delays now we just have the node B's or the E node B's in system architecture evolution SAE and we have now the gateways which are performing different functionalities for the user and data traffic. This results into higher bit rates because now we don't not only that we have lesser delay we have better throughput links which are connecting different gateways through fiber optic links all on IP. And definitely another important advantage of having this flattered architecture is the support for heterogeneity. Now not only do we have the system architecture evolution for release 10, 11 even up till 14 we also have the backward compatibility for other 3GPP technologies including the classical GSM the GPRS edge etc and certain other non 3GPP technologies as well. So having this flattered architecture means we are all set to encompass every technology what it may whatever it may be.