DSL and Cable modems are 2 forms of broadband connection systems. Now what exactly is a broadband system. Communication carriers or in simple words wires and cables are of 2 types.
1) Baseband - This is the type of media in which only one signal passes through the media at a time.
2) Broadband - In this type multiple signals can travel through the media at the same time. Cable that carried many channels is the example of this type.
So how do you define a broadband in reference to Internet access speed? Anything above 64kbps speed can be classified as broadband. We say 64 because modems can theoretically give speeds in the range of 56 kbps. The main advantages of broadband are that it is always’connected”, the speeds are considerably higher and you save a fortune on phone bills. The 2 main types pf broadband, which are available in India, are the cable and the DSL options.(The other option is Ethernet). In my previous opinion I had discussed DSL and now I will discuss the cable modem.
Cable Modem
Cable Modem is becoming a popular alternative among home users who prefer it to dial up access. Cable Internet means bringing the net to your house through the same cable that brings you TV channels into your TV. This is much simpler than the DSL network. It consists of the Cable Modem Termination System(CMTS) at the cable guy’s place or your provider and the cable modem at your place. The cable modem at your place will let you access the net through your Cable TV( CATV) network. These are of 3 types:-
1) External Modem - This is the most common type of modem used. It is similar to the dial-up external modem. One side of the cable modem will be connected to the coaxial cable coming from your cable operator and the other side connects to your PC through and Ethernet Interface. So u will need an additional network card. But now u also get cable modems with USB interface.
2) Internal Modems - These cable modems will fit inside your PC and usually have PCI interface. They are cheaper than external cable modems and being PCI will fir only inside a desktop PC. I guess Mac and notebook users will need an external modem.
3) Set-top Box - These are usually offered by companies like Samsung and jadoonet. They allow you to access the net using your TV and a keyboard. It consists of a cable modem, which will connect the cable from your operator to the TV at the other end.
Inside the cable Modem
although the various types of cable modems mentioned are different in thier appearance, they all contain the same key components needed to make them work. Let’s take a look at these components.
Tuner * - Internet data travels in the form of radio frequency signals over a cable network. Therefore a cable modem needs a device to send and recieve these signals. This is where the tuner comes in. It is inside the cable modem and connects to the cable coming from your cable operator. This cable goes through a splitter which separates the interet data from the TV programs. The data is trasmitted at different frequencies for upload and download. So a tuner contains a’diplexer’ which allows it ti handle both the upload and download. The Tuner receives digitally modulated QAM signals and passes them on the demodulator. QAM is a method of modulating digital signals to radio frequency signals.
Demodulator *- This part of the cable modem converts the radio frequency signals received from thte tuner into signals which can be fed to an analog to digital convertor. This in turn converts these signals to 0s and 1s. Then it is sudjected to a error correction test to check and problems in transmission. Then a synchronizer is uesd to make sure the digital signal stays in order.
Modulator * - This does the reverse job of a demodulator. It converts digital computer data( upload data) into radio frequency signals which can be trasnferred over the cable. It is also known as burst modulator due to the irregular nature of traffic between the user and the internet.
MAC * - MAC stands for Media Access Control. The MAC mechanism sits between the upload and download paths. It is used to share the media in a controlled and resonable way, so that all the users are able to access the net without any problems. For example, the cable operaor can control the bandwidth of a user by knowing his MAC address.
Interface * - The interface which can be Ethernet, PCI, or USB, trasfers data betwen your PC and the cable modem. Set Top Boxes(STB) dont have a PC interface, but connect directly to your cable operators cable. You then attach your TV and a keyboard to your STB to acces the net.
Because Cable is a shared media, i.e., the cable, which comes to your house, is used by the neighbors also. As more and more users are added to thte segment that you are using, the available bandwith will be shared.
Thanks a lot for reading my review and hope that you have found it useful. I have written about DSL in detail in my other review