 Moving on, now we look at how the security and generalized mobility are considered to be standard requirements and how the standard documents in the Y-Series address these areas. We'll start off with security. Understandably, security is the most crucial operation or I may say service to the usage of network infrastructure services and applications effectively. It is of concern to the service provider, to the telecom operator and of course, last but not the least, the end user. Several factors affect the provisioning of security to different levels. For instance, what all QS support is provided in the network because there's a trade-off usually associated with the level or depth of security that you wish to provide and the kind of quality of service that you would like to provide to your users in terms of the response time and the speed. Mobility, identity management, the network management. Let me talk about these three first. Now, if you recall, when we talk about mobility, we move from one network to the other. Moving from one network to the other requires exchanging credentials from the previous network to the next network. This requires some security infrastructure to be incorporated into the system. Identity management means if a certain user is known on Facebook with some ID and is known on Twitter with another ID, now needs to exchange information between Twitter and Facebook. What mechanism would be incorporated to ensure that there's no security breach with regards to the data of this particular user? Network management means that the entities or the network infrastructure is best geared or optimized to give performance. Of course, if the security requirements are well-defined, they are going to have an additional overhead in terms of the network management. This is of a very important concern. And also, lastly, the AAA that is authentication, authorization and accounting, the most well-known billing mechanism incorporated in the commercial side of the telecommunication service provisioning. AAA also has a direct bearing and a direct relationship with how and what kind of security is provided and through which functional entities should this security be provided. Security becomes increasingly challenging when it comes to NGN because of certain realities. The first one is the networks are encouraged to be more open because with standard telecommunication cable TV, the PSTN or PLMN kind of and the ISP kind of networks, the interfaces were well-defined. The infrastructure was more monolithic, but here the networks are encouraged to follow more open standards. So the services which are offered in one network are now available in another network. It means the user is available in one kind of network and is trying to access the services in another kind of network. So since there are no strict interfaces between these open or new kind of network integrating into the NGN as what happened in telecommunication networks, we have a problem. The problem is how to ensure that security remains the same and the kind of definition of security which exists in one kind of network is consistent with the definition of security in another kind of network. The services which are also provided by the application programming interface which is nothing but software in the client end such as the applets and on the server end which is the servlet. All we are left to do is we have to use the mechanism on need to do basis. So it means security in NGN now understands this and the recommendations, the device series recommendations are about providing security on need to do basis and providing the what best fits a certain situation. Since the ITF is the primary leader in providing security related documentation, the standards and the protocol implementations. So readily ITUT can benefit from the standardization activity that has evolved and is pretty much at a very stable place by the ITF. The next important consideration in the NGN recommendations why series is the generalized mobility. Now we know that ideally in network when a user is moving from one network is one subnet to the other or if it is an internet work movement then we are interested to provide mobility support through different access technologies. It means the wireless interface can change. The terminal or the handle device needs to talk to different wireless standards now. Now the interesting thing is if it was break and make or make and break kind of movement it would be less cumbersome. But the problem becomes slightly more complicated when there is movement or mobility involved while the user is using certain kind of services. Now this is a mobility requirement which is fairly generalized or which is I would say very broad. So it means that if NGN has to address that then some good recommendations must be presented. With the kind of recommendations certain challenges need to be considered for instance. Once we have different access networks different wireless technologies they have different air interfaces for instance Wi-Fi 3G 4G LTE LTE A etc. They all vary in speed in QoS and in kind of the handshaking or handoff requirements in these networks. The other issues are which are of course very important that different service level agreements or a priori contracts exist between these users and users and the service provider. Unless there is a uniform definition of mobility and the provisioning of service at a certain quality of service if there is no consistency we have a problem. So the generalized mobility aims or addresses all these by providing a possibility or it just encourages a plausibility to access these services regardless of the device that a user carries, the air interface or the wireless technology that is being used. So consequently we have some interesting definitions of mobility that we call as the horizontal handoff and the vertical handoff. The horizontal handoff is once the handoff or the handover during mobility is taking place within the same technology. So we have issues we have complications but not as much as in vertical handoff where the technology is changing and the handoff mechanisms change the air interface and the wireless technologies change. So the generalized mobility has to handle them all. Now it is required out of the network infrastructures whatever networks are going to be part of the NGN they have to be mindful that whatever service is being provided has to be kept independent of the underlying transportation mechanism. In simple terms whatever technology is being used to provide wireless connectivity because remember mobility is more of a concern in wireless networks in wired networks hardly mobility can take place and even if mobility takes place in wired environments it is too obvious and it is too simple to be addressed as a technology problem. So mainly we are talking about the wireless network mobility. So here the generalized mobility of the Y series recommends that there should be a bifurcation or splitting of the transportation or transport network which is underlying and the kind of services which are being offered on that transport infrastructure. So we say we have a transport stratum and we have a services stratum. Now the bifurcation or separation of these two strata results in providing the same service over different wireless and mobile ad hoc mobile network technologies.