Definitions and terminology

• Data Communications involves any transfer of data from one source to another, whether from Disk to memory, from PC to Modem, from PC to PC, PC to mini, or PC to mainframe, PC to Fax, PC to PC for video conferencing
• Most commonly, it refers to data transfers between a computer(s) , and terminals, or other computers.
• Whenever data is transferred from one computer or device to another, each individual character or byte is broken down into it's individual component binary digits or bits.
• These bits (0's and 1's) can then be transferred in a Serial, or a Parallel manner.

Before we move into the details of data communications, some terms need to be defined:

	Connectivity The ability to connect a microcomputer to other computers and sources of information via the telephone or other communication channels. These other computers can be micro-, mini or mainframe. The concept of connectivity expands the definition of computer competence to knowing about larger computer systems as well as micro- computers The growth of services such as Internet, where millions of users are connected, through a huge array of computers, means we all need to become familiar with the concept of connectivity.
	Telecommunications Communicating between different geographic locations, usually using some form of electromagnetic signal similar to that used for radio and television. Includes; Voice Fax Video Data
	Teleprocessing Data processing between different geographic locations.

• Voice grade. a channel, generally with a frequency range of about 300 to 3400 Hz.
• Suitable for transmission of speech or data in an analog form.

• Televisions are tuned to a channel (Channel 1, channel 2, etc..)

For a signal:

The number of complete cycles passing a given point in one second.

Electrical frequency is specified as the number of Hertz

• Television signals are sent as
• VHF - very high frequency (30MHz to 300MHz) or
• UHF - ultra high frequency (300MHz to 3000MHz)

For sound:

The number of vibrations per second.

• Bees beat their wings 200 times per second, so their sound is 200 Hz
• Mosquitoes beat at 500 times per second so a much higher sound.

• Difference between transmitted and received power due to transmission loss through equipment, lines or other communication devices.

• a measure of the information transfer rate of a data channel

• A unit of signaling speed equal to the number of signal events per second. Not necessarily the same as bits per second (bps) - rapidly being superseded by bps.

The rules for communication between like processes, giving a means to control the orderly communications of information on a data link. These may be either software or hardware

May be either

• Analog (such as voice based telephone system)
• Digital (made up of 0's and 1's)

[Rev: 18/8/98] Jun-97 © 1997-98 V/2-Com (Verhaart), P O Box 8415, Havelock North, New Zealand.