 Like we talked about the transmission of internet services through the UTP, unshielded twisted pair and we then discussed in detail the digital subscriber line technology. Similar to the UTP, another most widely prevalent and deployed technology for the transfer and transmission of television channels both analog and digital is the cable which is the coaxial cable that comprises a core and the cladding. Now the cable once deployed has now been thought about to be deployed for the transmission of internet services and others. In a couple of modules that we shall study, we will talk about the cable access network. We would look at the operation of it and then we would look at the complete architecture. Let's start with the history of it. The cable networks as we know them are basically the deployment of coaxial cables across residential and commercial areas. These were originally designed to broadcast the TV services. First the analog television channels were broadcast to the home subscribers it started off in US and later the digital televisions were offered using the same technology. The digital channels are different from the analog in the sense that the digital channels would offer something called a tele-text service. Anyways when these two technologies made inroads into the US market then the cable was then thought of to provide the internet service. Nowadays the cable networks are again most widely used like their DSL counterpart to provide the triple play services. Once we say triple play we already know it it deals with the voiceover IP, the services of both analog and digital televisions as a legacy service and then the internet. The coaxial cable once it is compared as a medium with the unshielded twisted pair it is much better in transmission characteristics as compared to the UTP. Number one it is better shielded in terms of noise it has a thicker copper core consequently it results into better frequency spectrum availability. So coaxial cable provides wider frequency band to be transmitted over it since it was initially meant for television and television needs the six megahertz spectrum so it was good enough to provide the downstream TV services. Now if we are going to take it up as a technology that also provides the two-way communication that is if you want to have the triple a services we would need not only the downstream traffic in the cable network architecture but we also need upstream traffic. Now since the inherent design was only downstream so we may have some some problem for instance there is an amplifier that is used to amplify the attenuating signal coming downstream so we also would be requiring some kind of amplification mechanism on the upstream and then we also have to look at how do we design this duplex communication is it going to be half duplex or full duplex for that it needed some proper adjustments so some efforts come in some of these efforts were from the famous cable lab and the other was from the ITF working group as a first prototype and it was pretty successful that was in cable network architecture to provide downstream transmission of data the cable television network was used as such it means the downstream traffic was transmitted on the from the head end head end is the operator side from the head end to the home subscriber but as far as the upstream requests are concerned because we know that in typical internet architecture if it is client server or peer-to-peer there is an expectation to have both sides of communication so the upstream traffic also needed to be carried in order to implement a very innovative kind of approach was adopted that is the hybrid kind of architecture in the hybrid architecture what happens is the user traffic from the user equipment to the operator side is carried on a different network for instance on a dial-up or on another leased line typically dial-up was used the dial-up would provide the non confronting and non competing traffic on the uplink only to make requests and according to the requests made that the downlink transmission would start the data rate since it is only the downstream traffic coming from the operator side to the user side very high data rates up to tens of megabits per second were allowed now the obvious advantage of using downstream for data transmission was that it had already had amplifier mechanism built in so longer reaches of coaxial cable were deployed to provide internet connectivity to far-flung areas there was a downside or a limitation of this mechanism however that is since the inherent nature of cable TV is that if a single TV channel is transmitted on the cable from the head end to the user side it is broadcast to all the users so likewise once the data transmission was sent downstream it would also be delivered to all the users so a mechanism would then be required to secure it to make sure that the unwanted or undesigned users would not receive it so advanced versions of the provision of internet over these coaxial cables was thought about will study about these in subsequent modules