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How Modem and DSL Works :

How Modem and DSL Works BY FAIZA & NISHAT


MODEM A modem is a device that enables a computer to transmit data over telephone or cable lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms. MO dulation and DEM odulation Conversion to analogue signal is known as modulation, conversion back to binary signal is called demodulation

Typical Modem Connection:

Typical Modem Connection 110011 110011 Modem PC PC Analogue signal Analogue signal


HISTORY BELL 103 by AT &T First commercial device available 1962 300 bps 1960 s To 1983 and so 1200bps Gained popularity in 1984 and 1985 2400bps Appeared Late 1990 and early 1991 56kbps Became the standard in 1998 ASDL 9Mbps Gained popularity in 1999


TYPES OF MODEM Câblé Modem cable modem is a device that is designed to provide a broadband Internet connection without the use of a phone line. Three types External Cable Modems Internal Cable Modems: Set Top Box Integrated Cable Modems

External Cable Modems :

External Cable Modems USB OR CAT5 CABLE COAXIAL CABLE Computer Modem Internet External modems are - Simple to set up, allow flexible usage but are more expensive than internal modems.

Internal Cable Modems: :

Internal Cable Modems: COAXIAL CABLE COMPUTER INTERNET Internal modems are Compact, Inexpensive but difficult to set-up (if not pre-installed with computer package).

Set Top Box Integrated Cable Modem :

Set Top Box Integrated Cable Modem TV MODEM COMPUTER INTERNET

Set Top Box Integrated Cable Modem :

Set Top Box Integrated Cable Modem INTERNET

DSL(Digital Subscriber Line):

DSL(Digital Subscriber Line) DSL is a very high speed connection that uses the same wires as a regular telephone. DSL is also known as xDSL with the x standing for various kind of technologies. It is a technology that assumes digital data does not require change into analog form and back. A DSL connection manages to squeeze more information through a standard phone line.

Types Of DSL:

Types Of DSL Asymmetric Digital Subscriber Line (ADSL): Most home and small business users typically use ADSL. The transfer of data from the internet to PC is much faster than the transfer from PC to internet. Downstream speeds for ADSL range from 1.59 Mbps, while upstream speeds are up to 1.5 Mbps, for a distance of 18,000 feet from the service providers premises. .

Slide 13:

Very high-bit-rate Digital Subscriber Line(VDSL): Provides high speed internet connection but works only over a short distance. Symmetric Digital Subscriber Line (SDSL). Does not allows to use the phone at the same time. But internet speed of sending and receiving data is same. Rate Adaptive Digital Subscriber Line (RADSL). This service is a variation of ADSL but the modem can adjust the internet speed .

Working Of A Simplified ADSL :

Working Of A Simplified ADSL INTERNET


Advantages DSL service is always on and we can still use the phone for voice calls. Broadband speed is much faster than dial up service. Fixed monthly billing , regardless of time usage. Digital data is directly transmitted to computer as digital data which uses much wider bandwidth for transmitting


Disadvantages DSL has one significant downside: As you move away from the central office ,the connection becomes slower. This results is distortion of signal

Distance Limitations:

Distance Limitations Precisely how much benefit we can get depends upon how far we are from the central office providing the ADSL service. ADSL It is a sensitive technology . As the connection length increases the quality decreases and the connection speed goes down.

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PC modem Central office ISP Internet