 In the earlier module, we just looked at the cable network service architecture in which we just briefly looked at how the internet service could be provided on coaxial cable. But after all, the internet service provisioning is based on a complete ISP kind of architecture in which we also have the IP level connectivity, the triple A services, the transmission of packet data to the IP cloud. So it means an entire set of services is required. So the cable network architecture is what deals with all these network related issues. We'll talk about Cable Labs, a pioneering company that started providing these triple play services over the existing coaxial cable. And then we'd look at the architecture and its internal detail. So the Cable Labs known for defining the specifications and the overall architecture for transmission of data over the cable networks. Primarily, the primary intent was to provide internet. However, later, the voice of our IP services were also integrated. So Cable Labs actually thought about an integrated solution. The integrated solution means that a couple of services can be offered on coaxial cable. It means it is more than just connectivity. It is more than just the downstream traffic issues and upstream traffic issues. It actually relates with the simultaneous provisioning of all these services, such as the continued services of the analog and digital channels, the transmission of radio on these cable infrastructure, high definition television, which requires very high data rate, video on demand, internet of course, and the voice over IP, not only voice over IP as in telephony, but complete set of services. Now, what we pick from here is the most important message that is in order to integrate these services, the Cable Labs needed lots of bandwidth and lots of frequency channels. And this is exactly what happens, that is on a single coaxial cable, multiple channels, that is, multiple frequencies are used to provide these services. Some of these services may be using the same frequency band. Some of these services might be using dedicated frequency bands depending upon their bandwidth requirement. So consequently, once all these services are to be provisioned, then some integrated approach has to be adopted. So the integrated approach is adopted in a way that different segments of the end-to-end network is understood and then it is designed in a way that one part of the network is not affecting the other part of the network design. For that, the Cable Network architecture is based on the home IP network side, that is, the user side, which deals with the provisioning of various internet-based services, including voice, including browsing, surfing, and others. Then there is something known as the DOCSIS architecture. We'll briefly talk about it. It is very important to first understand that the traffic, which is downstream and upstream, as we discussed in the earlier module, have to be carried through some proper mechanism and DOCSIS deals with that. Then the overall architecture, that is the packet cable network architecture. A packet cable network architecture means, as the name implies, it is the transmission of IP packets, which might be carrying literally anything over the existing cable network. And this needs to be integrated with existing internet infrastructure that involves, but is not limited to the core IP network and the overall internet infrastructure. So it means when we look at these segments, these segments can be seen to be mutually non-overlapping and they have some kind of exclusive design issues which must be handled differently. So in all, once integrated services have to be provided in this kind of segment-based network, a mechanism should exist, that is exactly what cable network does, to provide a transparent, transparent means there is no dependency requirement for various types of services in a very homogeneous manner, consistent manner. Let's look at the integrated network that achieves these integrated services while utilizing the coaxial cable. Let's look at the figure from the user or the customer premises. We have homes where the cable is laid right up to the pavement and to the curb. These homes have the cable modems. These cable modems are the customer premises equipment. The customer premises equipment works on behalf of all the devices which are there in the residence or in that home. Now from this customer premises device, the cable modem, then it actually is the scope of the DOCSIS architecture. DOCSIS is basically the data over cable service interface specifications. Now what happens is how data is carried is what is the scope of cable modem and the cable modem termination system. So it means the cable modem is now going to talk to its counterpart, the cable modem termination system. Now from the cable modem termination system to the network side, which deals with the integration or the aggregation of various kinds of traffic such as voice, video, data, etc. Every type of data traffic and service needs a different network. For example, PSTNs deal with voice call. The TV broadcasting network is different. Internet service provisioning needs ISP. So the packet cable network allows the cable modem termination system to have some kind of integration mechanism through which all this traffic can be carried to respective networks. And then we see the services network segment on the left-most side, which deals with different kinds of services. So it means what we can simply understand from here is if we now explain it from the left-hand side to the right-hand side, we shall see that there are different kinds of services, voice, video, data, radio, all these have their own networks. All these networks are connected through an integrated aggregated network which is the scope of the packet cable architecture, which in turn deals with the cable modem termination system, which is the intermediate gateway that talks to the home subscriber cable modem. So this is the complete end-to-end network architecture. The most important aspects to be understood here are the packet cable network architecture design and the DOCSIS specifications. We shall talk about these.