Understanding the network.pdf - Back to Home

• Radio transmission—It is achieved by sending electromagnetic wave forms
of a certain size (wavelength) and certain speed. The most familiar types of
radio transmission are ultra-high frequency (UHF) and very-high frequency
(VHF). UHF (100mm to 1m in length) wavelengths are used for satellites,
mobile communications, and navigation systems. VHF (1m to 10m in length)
wavelengths are used for television, FM radio, and citizen band (CB) radio.
Microwaves (10mm to 100mm in length) are used for telephone and satellite
communication systems.
• Lightwave transmission—It is used for line-of-sight transmission. It operates
on the same principles as optic fiber cable without theconnection carrier.
Transmission Signals
To send data across any type of medium, some type of encoding method needs to
be used. Data signals are transmitted across the transport media using varied
electrical signal.
The data encoding methods used to convey data over copper-based media operate
by sending electrical current to your home. Where direct current (DC) flows in a
single direction across a conductor, alternating current (AC) flows in both directions
across a conductor, alternating between positive and negative voltage.
NOTE
In case you forgot what you learned in physics class, here is a quick study on some
basic electrical terms:
• Current (I)—The number of electrons that pass a given point. Current is
expressed in units of amperes or amps.
• Voltage (V)—The electrical pressure or force of the DC flow. Voltage is
expressed in units of volts.
• Resistance (R)—The ability of the medium to resist the flow of current.
Resistance is expressed in units of Ohms.
• Power (P)—The amount of work performed by a current. Power is
expressed in units of watts.
• Root-mean-square (RMS) voltage—The AC voltage equivalent to DC
voltage that yields the same force. RMS is the transition point (0)
between the positive (+) and negative (-) flow.
• Impedance (Z)—The opposition created by a conductor to the voltage
change +/-of the AC flow. Like resistance, this is expressed in units of
Ohms.
• Frequency (Hz)—The number of cycles that occur within one second.
Frequency is expressed in hertz.