Modem

• A modem is a network hardware device or a program that enables a computer to transfer data to another computer network through telephone lines.
• Modem are sending the amount of data in a given unit of time is expressed as bit per second (bit/s) or bytes per second (B/s).





• Computer information is stored digitally, so modem modulates the digital signal to analog signals for a conventional copper twisted pair telephone line.
• And again demodulates the incoming analog signal and converts it to a digital signal for digital device.

Types of modem

External modem

• External modem is an external unit of computer.
• It is connected to the serial port COM1 or COM2 of the computer by means of a cable.
• It is also linked to the telephone line through telephone walk Jack.
• An external power is also supplied to it.
• It is more expensive. It has very high data transmission speed.

Internal modem

• An internal modem is a circuit board (or modem card).
• It is installed into one of the expansion slots inside the system unit of the computer.
• It is less expensive than external modem.
• Its data transmission speed is slower than external modem.

Wireless modem

• Wireless modem consists of modem and antenna.
• It is also known as radio frequency modem.
• It transmits the data signals through air.
• This type of modem is used with laptop computers and desktop computers.

Features of modem

• Speed
  Speed is measured in Bps, Kbps, Mbps, Gbps.
• Self testing
  Modem can test the digital connection on computer and analog connection on remote modem.
• Auto dial/redial
  Smart modem can dial the phone number and auto redial if a busy signal is recived.
• Auto answer
  Modem can automatically answer when incoming call comes in.
• Voice over data
  A voice conversation to take place while data is being transmitted.

Applications

Point of sale

• Anytime you pay via credit card or debit card there is a modem behind it transferring that data and returning an approval or denial quickly and in the case of dial-up solutions with less costs associated.
• Like ATM cash machine, credit card payment terminal in restaurants, movie theaters or retail stores.

Remote management

• Modems can be installed in remote locations at off-site locations, tight enclosures or inside sensitive locations.
• Like traffic signal there is a modem to alter signal timing from headquarters to regulate traffic flows.

Machine to machine

• Medical devices transferring test results to a computer at a doctor's office.

Data transfer