Computer Networks

Analog Transmission

Analog transmission - information is represented as any value, but computers handle only digital information


To transmit binary signals generated by a computer on a switch, must use modem (short for Modulator/Demodulator) to modify (modulate) analog signal to encode binary information. (How Modems Work by Marshall Brain, HowStuffWorks)

Modem is always in either 0 or 1 state.

To receive signal, modem modifies (demodulates) information and converts it to digital form to send to the computer.

Bandwidth is the capacity of the transmitter/receiver connection.

The amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits per second (bps) or bytes per second. For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz).

The bandwidth is particularly important for I/O devices. For example, a fast disk drive can be hampered by a bus with a low bandwidth.

Early bandwidth: 1200, 2400, 4800 bps

Modern modems: 28,800; 33,600; 56,000 bps

To achieve higher bandwidth, need dedicated communication links (rather than switched links) - physical permanent lines that connect two or more computers

Can have twisted-pair copper wire, co-axial cable, or fiber-optic cables.

High Speed Communications

Fiber-optic cables - send signals using light waves at much higher speeds and fewer errors

Gigabit networking - speeds above 1,000,000,000 bps (Gbps)

Wireless communication - radio, microwave, or infrared signals; no physical connections (How Wireless Internet Works by Jeff Tyson, HowStuffWorks)

Why do we need such high capacity, high speed communications?


CS1104 Main Page
Last Updated 2002/02/13
© L.Heath, 2000, updated by J.A.N. Lee.