ITM5100-Exam1_deck_5723694 Flashcards
Identify various types of media as being either analog or digital. Take a Polaroid instant photograph (on photographic paper) as an example. The scene would be analog but you are interested in determining whether the media (the photographic paper) stores or communicates the image primarily as an analog or digital process.
Analog. Photographic paper uses a light-sensitive chemical process to imprint the image. Different types of photographic paper have different sensitivities and resolutions (which can make the photograph appear grainy) which might sound like a digital process but it isn’t electronic and doesn’t have rigidly defined levels of brightness and color. If some distortion (noise) gets mixed in with the photograph it is almost impossible to remove the distortion. The photo paper has primarily analog characteristics.
President Nixon’s Oval Office tapes were used to record conversations between the president and his advisers. What was the information and what was the media?
The info (voice conversations) was analog. The magnetic tape media was analog.
You downloaded some music files from iTunes to your iPhone. Are the music files analog?
No, they are digital representations of analog music (information)
We introduced two types of standards. What were they called? Know how they are different.
De jure & De facto
Know the names of the seven layers of the OSI model.
Physical, datalink, network, transport, session, presentation, application
Which layer of the OSI model includes physical addressing?
Datalink or L2
Which layer of the OSI model includes logical addressing?
Network or L3
Which layer maintains multi-transmission sessions between computers?
Session
Which layer can include encryption or decryption and conversion of text into character codes?
Presentation
Which layer combines bits into frames?
Datalink
Which layer encodes bits as voltage levels or waveforms carried on guided or unguided media
Physical
Which layer performs flow control and sequencing or ordering of packets?
Transport
Which layer is characterized by the HTTP protocol?
Application
Convert this binary number (01) to hexadecimal and decimal
01, 01
Convert this decimal number (10) to binary and hexadecimal
1010, A
Convert this hexadecimal number (F) to decimal.
15
What is the definition of convergence?
The merging of two technologies or industries
How many layers are in the TCP/IP network model?
4 -
Order the following networks in terms of INCREASING area of coverage: WAN, PAN, MAN, LAN
PAN, LAN, MAN, WAN
Is the Internet and example of a LAN?
No, it is a WAN.
When talking about making a LAN connection, what does the acronym NIC stand for?
Network interface card
Name at least one advantage of a digital system over analog
Relative immunity to noise. Noise can be filtered.
Name at least one vantage of an analog system over digital
Narrower bandwidth, more faithful reproduction of the information (when noises absent)
According to the Nyquist theorem, you should sample at least what?
At least twice the highest frequency
Name some character encoding schemes
ASCII, EBCDIC, Unicode
What are three basic parameters of a signal?
Amplitude, frequency, phase
What unit is used for relative strength or attenuation measurements
dB or decibels
10 dB represents what multiplication factor?
10
3 dB represents what publication factor?
2
-3 dB represents what attenuation factor?
1/2
When combining dB, what mathematical operation do you use?
Addition
When combining amplification factors, what mathematical operation do you use?
Multiplication
3dB and 10 dB combine to give you how many dB and what amplification factor?
13 dB and an amplification factor of 20
Negative amplification (or attenuation) is represented by a positive or negative dB value?
Negative
How many ways can you combine analog or digital information with analog or digital signals/waveforms?
4
What is a term for the combination of digital data and analog signals?
Keying
Frequency shift keying encodes digital data using different what?
Frequencies
A phase reversal or waveform inversion is an example of how many degrees of phase shift?
180 degrees
What is a variation in an waveform’s parameter (amplitude, frequency, or phase) to embed information
Modulation
Why do we modulate information on to waveforms at different frequencies?
To take advantage of different transmission or propagation characteristics. For example, voice frequencies are low and would require a very long antenna to transmit. Additionally, if we transmitted all voice at voice frequencies we wouldn’t be using all the available spectrum.
What theory tells us that always forms, no matter how complex can be constructed from carefully selected basis waveforms of various frequencies and amplitudes?
Fourier. A basis waveform is a fundamental family of waveforms like sinusoids as opposed to square waves
Sharp edges in a waveform normally result in more or less frequency content?
More
If you have a transmitter with 3dB of gain followed by an antenna with 3dB of gain, how much gain do you have, in dB and as a multiplication factor?
6dB or 4x
If you have a transmitter with 3dB of gain followed by a long cable with 3dB of loss, what is the overall gain in dB and as a multiplication factor?
0dB or 1x. (3dB – 3dB = 0dB). Remember, 3 dB of loss is negative. Zero dB represents no gain and no loss, so the multiplying factor is 1, which is neither amplification nor attenuation of the input signal.
Is a continuous waveform analog or digital?
Analog
Is a stepped waveform analog or digital?
Digital
Can a single waveform be composed of multiple frequencies?
Yes! For example, a square wave could theoretically have infinite frequency content
What is the frequency domain representation of a signal called?
The spectrum
What three parameters does Shannon’s equation use as inputs?
Signal power, noise power, and bandwidth
When considering Shannon’s equation, how should we increase or decrease the values of signal power, noise power, and bandwidth to send more data, faster?
Increase signal power, decrease noise power, and increase bandwidth
What quantity does Shannon’s equation allow us to calculate?
The theoretical maximum data rate for a channel
Is free space loss dependent on distance?
Yes. It increases with distance.
Is free space loss dependent on frequency?
Yes. It increases with increasing frequency.
The difference between the highest and lowest frequencies in a waveform is sometimes called the what?
Bandwidth
If a waveform completes three cycles in one second, what is its frequency?
3 Hz
If a waveform makes three waveform/signal changes in a second what is its baud rate?
3
If a waveform sends three bits in one second what is it bit rate?
3 bps
Quadrature amplitude modulation is a combination of what to waveform parameters?
Amplitude and phase
Amplitude shift keying uses what waveform parameter for modulation?
Amplitude
Name an encoding scheme that transmits four bits of information using five bits of waveform
4B/5B
With pulse code modulation you can get a better representation of the original analog waveform by increasing what two things?
The sampling rate and the amplitude resolution (number of bits used to encode the amplitude values)
Twisting two wires helps eliminate what?
Cross talk or coupling (electromagnetic interference between the two wires which are probably carrying different signals)
Guided or unguided media? What is Copper wire?
Guided
Guided or unguided media? What is the vacuum of outer space?
Unguided
Guided or unguided media? What is fiber-optic cable?
Guided
How does shielding help cables carry more data, faster?
It reduces interference from outside sources?
How does shielding make cables more secure (from a secure communications perspective)?
It reduces the leakage of electromagnetic waves to the surrounding environment
What type of communications is characterized by intermittent data?
Asynchronous
What type of communications is characterized by continuous data?
Synchronous
What type of communications is used for real-time applications such as video or audio?
Isochronus
What communications is characterized by full two-way simultaneous transmissions?
Full duplex
Half duplex
Two-way communication, but only one way at a time
Simplex
One-way communication
Interface
A boundary or interconnection between two things
Official standard (or de jure)
Standards there created by standards development organization such as IEEE or ISO
De facto standard
Standard created by one or more commercial organizations for a new technology they may be developing
Name 4 components to an interface standard, as discussed in class
Electrical, chemical, functional, and procedural. Electrical covers things like voltage levels. Mechanical covers the physical connector size shape and pin configuration. Functional describes the functions of the pins. Procedural describes the sequence of steps for establishing, maintaining, and terminating a connection.
Differential or balanced signaling
Often used to transmit data with a high and a low data line. Ones and zeros are represented when the two lines, which are referenced to each other, swap levels. This is the predominant technique used in high-speed data transfer today.
Polling
A technique for negotiating access to a channel or medium whereby a master device asks each of the connected devices, in turn, whether they have any data to send. Similar to a teacher calling on students one by one in the classroom.
Asynchronous
Transmissions that are intermittent and not synchronized to a reference clock signal. Asynchronous frames are normally marked by a start bit, stop bit, and parity bit. Human interaction with a computer is normally an asynchronous process, such as someone typing on a keyboard.
Synchronous
Transmissions that are referenced to a clock signal. A large amount of data can be can be packed into a frame making this technique more efficient than asynchronous. Data transfer from between devices could easily be synchronous, because there would normally be a large backlog of data (such as a file) that could be formatted and sent efficiently as a block.
Parity
Parity is used to detect an error. Parity can. be even or odd. The parity bit is used to make the number of ones in a frame even or odd.
Isochronous
This is a combination of asynchronous and synchronous communication techniques to send real time audio or video. USB supports isochronous communication.
FDM
Frequency division multiplexing. This technique is uses a communications medium more efficiently by combining multiple channels or streams of data for simultaneous transmission on different channel frequencies
TDM
Time division multiplexing. This technique combines data from different streams or inputs by interleaving segments of the data in time and transmitting them on the same frequency or range of frequencies. Remember the two types discussed in class: synchronous and statistical.
Discrete multi-tone (DMT)
A form of FDM used in digital subscriber line (DSL) systems
Synchronous TDM
A multiplexer accepts input from attached devices in a fixed pattern.
Statistical TDM
A multiplexer accepts inputs from attached devices, and skips devices that don’t have input. This scheme is random compared with synchronous, but is more efficient. Because the sequence of data is unpredictable, transmitter must embed some information (address and length) in each frame to help the receiver interpret the incoming data.
WDM
Wavelength division multiplexing. This is a form of frequency division multiplexing used over optical fiber. Each input stream can be a different rate.
CDM
Code division multiplexing. This technique assign unique codes to each input channel and allows simultaneous transmission of multiple channels in the same time and frequency space. A single bit is modulated using the code. This technique is very similar to direct sequence spread spectrum (DSSS)
Lossless compression
Compressed data can be re-created (on decompression) in its exact original form. Examples include runlength and Lempel Ziv.
Lossy compression
Some of the original content is lost in the compression process. Examples include MP3, JPEG and MPEG. A human can overlook or fill-in the missing data (based on their perception) and still understand the basic information content in the original message.
