Chapter 3 Flashcards
What happens in network
Encode data as energy. This energy can be electrical, light, radio, sound. Transmit that energy. Decode that energy at destination into data.
What are types of transmission media
copper, glass, air, radio wave signals, coaxial cable
Why copper wire use widely
Because of low resistance to electric current, inexpensive, easy to install
What are 2 major types of transmission media
- Guided media (Physical path e.g. copper wire)
2. Unguided media (No physical path e.g. radio wave)
What about optical fiber
It uses light for transmission
What are transponder and transreceivers
They send and receive data
What are geosynchronous satellites
Placed in an orbit of 35785 km and sync with the rotation of earth
What are low earth satellites
Rotates faster than rotation of earth at 200-400 miles above on earth. They are in arrays. It means they communicate with each other and with the earth.
What is the difference between RF (radio frequency) and microwave
Microwave is electromagnetic radiation which can carry more data than low frequency RF transmissions
What is infrared
Also known as IR. Remote control use it. It is inexpensive wireless communication and is limited to small area.
What is asynchronous communication
In asynchronous communication, the sender and receiver do not need to sync before the transmission begin. In this technology, the receiving hardware must be ready to accept and interpret signal whenever it arrives.
What are standards in communication
Standard specifies both the timing of the signals and the electrical details of voltage and current.
What is most widely used standard for communication
RS232-C
Does character start with a start bit (0) and ends with the stop bit (1) in RS232-C
Yes
What is baud rate
The number of changes in the signal per second
What is bps
bits / second
What is framing error
If the voltage measurement do not all agree or if the stop bit does not occur exactly at the same time expected, framing error occurs.
What is full duplex asynchronous communication
It is type of asynchronous communication. In this, electrical circuit requires at least two wires, one of them to carry the data signal, the other is used as the return path, called ground. This simultaneous transfer in two directions are known as full-duplex transmission. The data send and receives on both sides at the same time.
What is modulation
We use a high frequency signal and send our information on it for long distance communication. On receiving site, we demodulate signals. To send data, transmitter slightly modifies the original information by using a carrier. Such modifications are called modulation.
What are 3 types of modulation
- AM (amplitude modulation)
- FM (Frequency modulation)
- PM (Phase Modulation)
What is amplitude modulation
Only amplitude changes
What is frequency modulation
Only frequency changes
What is phase modulation
Only phase changes and amplitude, frequency remain constant.
What is modem
Modem is a hardware device that combines both modulator and demodulator in a single device.
What is modulator
A modulator is a hardware circuit that
- Accepts Sequence of data bits
- Applies modulation to a carrier wave according to the bits.
What is demodulator
A demodulator is a hardware circuit that
- accepts a modulated carrier wave
- recreates the sequence of data bits
What is multiplexing
Transmit two or more signals simultaneously over a single wire. It can be done by using different carrier frequencies.
What are 3 types of multiplexing
- FDM (Frequency division multiplexing)
- WDM (Wave division multiplexing)
- TDM (Time division multiplexing)
What is FDM
Using multiple carrier frequencies to allow independent signals to travel through a shared channel.
What is WDM
Same concept at FDM with a difference of using optical fibers
What is TDM
Same concept but sources takes turns to send data
What is the difference between statistical and synchronous TDM
Synchronous TDM gives each source opportunity to send data and statistical TDM does not give chance to a source that does not have data to send.
