 There are some very interesting applications of the Metropolitan Ethernet network. We are going to look at one such situation. As we know that mobile communication actually depends on the network infrastructure including the base stations, base station controller, the mobile switching center as in I am just giving you the example of 2G networks. In the case of 3G these devices are known as for instance Nord B, E-Nord B, Home E-Nord B as in 4G. Now these devices are essentially required to have very high connectivity at a very high data rate with very high availability with each other. So there is an interesting application of the Metropolitan Ethernet network to provide the backhaul service. Backhaul service means that not the air interface but the wired interface in the telecom sector is now being migrated to the Metropolitan Ethernet network technology. So the essential background of it is as we already know that mobile networks have actually all gone to IP networks. Now this is more of the evolution in terms of the access. We have already seen that starting from 2.5G, GPRS, Edge, HSPA to 3G and then in 4G as well. However the transmission between the network elements such as the base stations and the core such as on the access side we have base station, BTS, BSC, Nord B as in 3G, Radio Access Network and on the core side the core side actually can have the radio network controller or a gateway node as in the 4G networks. Now if you really want to provide very high connectivity at a very high data rate with high availability we have to think about providing this service through Metro Ethernet. The Metro Ethernet connectivity actually needs to take different forms and needs to provide a lot of flexibility because all these technologies starting from 2.5G, 2.4G and 5G even depends on a variety of factors. For instance what is the capacity which is required to provide this backhaul? What are the mobile standards like the ones some of these that we have just recapped and which compatible transportation technologies are already there and how would they best fit with the Ethernet technology? Now this is an interesting figure this shows us how the mobile network radio access through base station and the network controller is implemented through the existing technology that is the TDM time division multiplex technology such as SDH synchronous digital hierarchy sonnets synchronous optical networks that's the current situation but in terms of the Metro Ethernet then we actually have to think about establishing the VLAN kind of connection that is Ethernet virtual connection. And then there are some connectivity interfaces or demarcation points that we know as the user to network or the network to network interfaces. So here we have actually the UNI of the customer side UNIC on the left hand side in figure A radio access network customer equipment with TDM. So TDM is basically the one that involves legacy network. So once we want to introduce the metropolitan Ethernet network backhauling then we have to look at it from the UNI perspective. So we have the UNI and on the customer side we have the UNI and on the network side. We have the generalization of the metropolitan Ethernet network once we have the connectivity using MEN hardware. In the figure below what is different from above is that here we have the TDM legacy network that we already know but here in the lower case we have the extension of the metropolitan Ethernet network connectivity scope not only between the UNI of the customer side. We actually have now deployed the customer equipment and we have enabled it with MEN the metropolitan Ethernet network technology right from the exercise that is the base station and we have directly established a link with the core network using the metropolitan Ethernet network technology. So in simplest terms if you want to understand it we can say that the scope of metropolitan Ethernet network is actually dependent upon the existence of the technology which exists beforehand. For example in the figure above we have the scope which is between the UNI and the NNI within the service provider. So the service provider is purely responsible for providing translation between the interfaces and it has got nothing to do with the N networks that is with the radio access network. Whereas in the figure below now the radio access network itself is involved in translating the traffic as per the metro Ethernet network at its own. So it needs an interface directly at its own. So the scope is essentially now brought down to the radio access side. So the metro Ethernet network is actually used by the operator to provide backhaul to a mobile service provider and it is done through UNI and the scoping of UNI can be the responsibility of the service provider as such in the core side or it can be done at the access side provided the radio access network equipment the RAN CE is connected to mobile backhaul via the interface at its own. Now the radio access network customer equipment is a very broad term because depending upon the technology it can actually mean the radio network controller that is used in 3G and 4G networks. The gateway used in 4G networks it could actually be the location of multiple controllers or the gateways not only one and then it could be as simple as a base station, node B or any other specific access radio access device which is placed on the air interface side. If there is a TDM interface as we have just seen in the diagram that if the radio access network customer equipment has a TDM interface then it means some kind of service emulation is performed to make it integratable or interfacable with a metro Ethernet network. So it means that there are certain techniques such as the circuit emulation service or the PDH circuit which are traditional TDM technologies. So if you really want to provide metro Ethernet service to the to the end network or to the access network it is very important that you don't have to change the interface for the end user. That is exactly what we saw in the figure above. However, if the metro Ethernet service exists with the end network that is at the access side so the backhauling becomes an all MEN affair. So if the customer equipment of the mobile operator already has the Ethernet interfaces so it will support all the functionality that we have seen metro Ethernet network can provide including the E-Line, E-Lane and E-Tree. So this is the recap once again we have the figure above that is regarding the TDM emulation that is required for the for the access network but in the figure below the access network already has the metro Ethernet network infrastructure so there is no such requirement for TDM emulation.