 Now, we are going to look at a very important concept in NGN, that is, different operators, different service providers come together to accommodate inter-operator traffic exchange to allow a wide array of users to communicate with each other. The very notion of Federation is important, not only to the world but also to NGN. Here we look at how the Federation is realized in the context of NGNs and how specifically peering takes place between the group of operators. Federation as a formal concept was taken up by the SIP peering working group in the ITF. It defines peering in Federation as a group of service providers which are willing to agree to share information with each other on behalf of their users via the session initiation protocol. This helps them to come on a unified platform for settlement in terms of tariffs, the policies and rules which they implement, and the technology that they use. It helps them to establish seamless interconnections. Federation actually is nothing but a like-minded membership with operators having similar network technologies, more or less similar topologies. Their sizes are also comparable and the business strategies that they use are also quite similar. Since these operators come close to each other to exchange the traffic, so the most natural choice for them to exchange the traffic type is the voice over IP. This leads us to the concept of voice over IP peering that is establishing groups, multicast groups or unicast groups within the Federation to exchange traffic. Now, the concept of Federation and peering helps them to achieve the reduction in overall management costs in bilateral agreements. In voice over IP, the concept of peering is different. First of all, the voice over IP peering actually means that it is not a peer-to-peer connection. It means it is not between two end hosts, rather it is between two members of a Federation which come together and utilize a common NM based directory to exchange information for their voice over IP users on the SIP platform. Using the concept of peering, they come with some natural advantages. First, this helps them to implement controlled routing. Controlled routing is quite similar to the concept of strict source routing in IP version 4. It is an extension feature which was available in IP version 4 right from the RFC but it was hardly utilized because the ISPs wanted their users to enjoy some flexibility. But having a controlled routing actually encourages limited interaction only between the peering members in the same Federation. So essentially the hardware or the switches that belong to these providers establish virtual circuits or dedicated connections amongst themselves. Then the concept of next hop routing is used in these networks to allow the peering networks to share information with each other in the shortest possible manner. This helps them to achieve better network coverage and reachability. It is quite similar to the PSTN routing model in which the dialing number and the dial number are connected through the nearest group of intermediate exchanges. Now it is also important to appreciate that when we talk about the concept of federation and voice peering, we need to understand if the world has given it due attention. So first of all, we will start with that although it offers immense cross-platform interoperability because different hardware and software based network and service providers as long as they agree to use SIP and NM directories, any IP session from any computer or any network to any computer on any network can be realized. And the application could be any application from any vendor as long as it is implementing voice over IP that is compliant with SIP. With all these features, it is expected that this model of federation and voice peering should take over the market. But experience tells that it's not exactly as such because the middle man, which is the regional and the global ISPs are not dead yet. So they do keep their share or they do keep their business interests in mind. So the concept of absolute peering is not possible as it is desired. But we can't stop to appreciate what all additional benefits we can get from the peering and federation. This certainly helps us to reduce the concept of PSTNs and we can obviate the classical kind of circuit switching in which we'd have dedicated call termination, settlement and management infrastructure in which the calling party and call party have to be more strictly dovetailed with each other. Here it's quite flexible. The voice over IP peering platforms actually allow not only voice over IP as in audio visual chat but for video streaming as such, for exchanging messages for the push to talk services and even online games. All these can be realized through the voice over IP peering in the federation.