 Hello and welcome to lecture on model learning outcomes by the end of the session student will be able to explain the working of modem illustrate the types of modem explain the feature of modems you may pause here the video and find the answer to this question what is the need of modulation in a communication system answer to this question is we want to make the signal transmission immune to the noise as well as the signal to transmit more distance with low losses that is the need of modulation that's why we go for the modulation of a signal before transmission what is modulation modulation is a process of conversion of digital signal to the analog signal the three types of modulation techniques are first is AM amplitude modulation second is frequency modulation third is phase modulation in amplitude modulation the amplitude of the carrier signal is varied in accordance with the amplitude of modulating signal in frequency modulation the carrier frequencies change in accordance with the modulating signal in phase modulation the phase of the carrier is changed or varied in accordance with the information signal. Modem is an essential hardware for any user to access the internet. Without a modem, a user cannot access the internet. The modem word, it came from the two words, modulator and demodulator. Modem is a computer peripheral that allows us to connect and communicate with other computers via telephone lines. Modem converts binary signal or digital signal into analog signals for transmission over the telephone lines. And convert this analog signal back into binary or digital format by the process of demodulation on the receiver end. You always need a pair of modem for communication between two computers. Let us see the structure of data communication through modem. In figure one, you can see the communication between two computers over the existing telephone lines. The computer generates the digital data to transmit over the transmission lines or telephone lines. This digital data is converted into analog signal by this modem. Then that analog signal is transmitted over the existing telephone lines to the internet service provider. And then after it goes by a predefined process of networking to the destination. And on the destination side, once again, that analog signal is converted into digital by the modem. Let us see the working principle of modem. Figure two shows the generalized block diagram of modem. In terms of DCE and DTE, modem is a DCE device, while computer or terminal is a DTE device. Computer generates digital signals. Those digital signals are converted into analog signal by the modulator circuit present inside the modem. That analog signal travels over the telephone lines to the intended destination. On the destination side, the modulator circuit of modem, sorry, on the destination side, the demodulator circuit converts the received analog signal over the telephone lines into digital signals and provides the digital signal to the computer or terminal. Let us discuss the modulator block. Modulator is a unit which is used to convert the digital data received from computer into analog signal for transmission over the telephone lines. The modulation is done by adding a carrier signal to the digital signal. Figure three shows how the digital data is converted into analog by the process of amplitude modulation, demodulator. Demodulator is also a unit in a modem which is used to convert the analog data received from telephone lines into digital. And those digital signals are provided to the computer. Demodulation is done by eliminating the carrier signal from the received analog signal. Figure four shows the demodulation process. The types of modem. There are two types of modem, external modem and internal modem. We will discuss each in detail in the following slides. First type is external modem. Here in figure you can see that the external modem resets outside the computer next to the computer and it is connected to the computer via a straight through serial cable. And modem, on the other hand, is connected to the telephone line. External modem is a separate device and resets outside the computer and connects to the computer using a serial port with RS232 standard cable. A 9 pin or 25 pin serial cable connects the serial port to the modem. So we always do not need to open the CPU for modem installations. The setup of external modem is faster and easier than the internal modems. External modem requires additional power source and extra wires for connection with the computer. External modem features light on the front side so you can monitor the connection status, whether it is powered on or communicating with the other device or not. The second type of modem is internal modem. Here in figure you can see that this modem resets inside the computer and appear as if it were an external modem. Internal modem is fixed or sits inside a computer. Nowadays, internal modem is integrated on the motherboard of your computer. Internal modems can be plugged directly into PCI, peripheral component interface, or ISA expansion slots. Internal modem contains its own UART universal asynchronous receiver and transmitter. There is no need of extra wire for installation of internal modem as it is installed or it sits inside your computer. Internal modem obtain their power from computer's power supply, so there is no extra power supply required. Internal modems are not visible from outside the computer, except you can see it from the back of your CPU unit. Features, first feature is speed. Typically, the modem speeds are 300 kilobits per second, 600, 1200, up to 28.8 kilobits per second. Atto answer feature. Most modems have ring detect capability and can automatically answer the telephone when an incoming call comes in. Means if you have a ring incoming on your telephone line, it can detect self-testing feature. Newer modems have this self-testing feature. Some modems have this ability to test the digital connection to the terminal or computer and analog connection to a remote modem itself. The next feature is voice over data. Voice over data modems allows a voice conversation to takes place simultaneously while data is being transmitted or received. But on both the sides, that is on source as well as on destination, the modem should have this feature of voice over data. Next feature is synchronous or asynchronous transmission. Newer modems allows us to select the choice of synchronous or asynchronous transmission of data. You can select either. Normally, modern transmission is asynchronous. Next feature is atto dial or re-dial. Smart modems can dial the phone number and atto re-dial if a busy signal is received and keep on re-dialing the number. The last, how to install a modem. You do not need to install the internal modem, but you need to install the external modem. External modem installation is very easy process. You just have to connect the external modem using RS-22 cable to your computer. You have to insert the installation CD. Once the installation is done, then you have to restart your computer and you have to just test its functionality by the options provided in the accessories. These are the references. Thank you.