Presentation on modem

modem, types and use in communication system, speed depending on modem

1. Digital communication technology MODEMs Presented by: Patil Dnyandev Bhausaheb 1

2. 2 What is modem ? Modem is abbreviated for Modulation and Demodulation A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal of modem is to produce signal so that it can be easily transmitted over analog line and decoded to reproduce the original data.

3. 3 Key components: Transmitter (modulator), Receiver (demodulator). Control unit (auto dial & auto answer ). Power supply .

4. 4 Transmitter (modulator) and Receiver (demodulator) Modulator converts digital signal into analog form to transmit over analog telephone line . Demodulator converts analog signal into digital. Different modulation techniques are used to modulate signals, but at transmitting side, the final output of modulator is analog signal and input is digital. Different types of modulation: There are many techniques of modulation, depending on which modems are classified.

5. 5 Modulation techniques Frequency Modulation. Amplitude Modulation. Phase Modulation. Combination Modulation.

6. 6 Auto dial/auto answer There are different commands used to communicate with modem. AT commands are used for auto dial or auto answer. Control unit responds to AT commands and takes action according to command. Control unit (auto dial & auto answer)

7. 7 Classification of modem Modems are classified as follows: 1. Operation mode: Simplex: Only transmit or receive data. Half-duplex Transmit or receive data but one at a time. Full-duplex Transmit or receive data simultaneously.

8. 8 2. Synchronisation : Synchronous : Operate in the audio range. The usual modulation method is the phase modulation. Can handle a continuous stream of data bits but requires a clock signal. The data bits are always synchronized to the clock signal. There are separate clocks for the data bits being transmitted and received. Asynchronous: Most of the modems that operate in slow are asynchronous. Asynchronous modems operate in FSK (Frequency Shift Keying) modulation. Can handle data bytes with start and stop bits . It does not require clock pulse. Modems classification continue…

9. 9 3. Modulation: AM: FM (FSK): PM: Modems classification continue…

10. 10 Modems classification continue… 4. Transmission media: Dial-up: Dial-up modems can establish point to point connections to the PSTN by manual or automatic dialing or answering. Dial up modem uses a carrier that is an audible tone carried through twisted pair cable. Radio : Used to send data over radio frequency signal . Cable : A cable modem is a device that enables you to hook up your PC to a local cable TV line and receive data at about 1.5 Mbps optical: Used to send data across a pair of glass fibers using light. Such modems use entirely different technology than modems that operate over dedicated wires .

11. 11 Data terminal equipment (DTE) is connected to modem using digital signal. The modem is connected to telephone exchange office over analog telephone line using analog signal. The two exchange offices are connected to telephone network. Digital data is encode to transmit over analog line at transmitting end and again it is decoded to digital form by modem to represent data at receiving end. Communication system

12. 12 Techniques used to increase data speed After traditional modems reached their peak data rate, telephone companies developed another technology, DSL, to provide higher-speed access to the Internet. Digital subscriber line ( DSL ) technique provides high-speed data rates over conventional telephone line and the existing local loops. Types of DSL: ADSL: Asymmetric Digital Subscriber Line. SDSL: Symmetric Digital Subscriber Line. HDSL: High-Bit-Rate Digital Subscriber Line VDSL: Very-High-Bit-Rate Digital Subscriber Line (VHDSL).

13. 13 ADSL: ADSL is type of digital Subscriber Line that provides faster data transmission over copper telephone lines than Dial-up modem . It provides high speed of down link.

14. 14 SDSL: SDSL is type of digital Subscriber Line that is exact opposite to ADSL. It provides Low bandwidth for upstream than downstream.

15. 15 VDSL: VDSL provides faster data transmission than ADSL over twisted pair telephone line or untwisted pair line . It provides high speed of downstream up to 52 Mbit/s. It is common in home network. Very-High-Bit-Rate Digital Subscriber Line (VHDSL ).

16. 16 HDSL: It was the first DSL technology . It provides bit rate of 1.544 and 2.08 Mbit/s. High-Bit-Rate Digital Subscriber Line

17. 17 Thank You!