Test 1 Study Guide Flashcards
1
Q
What are the characteristics of a data communications system?
A
Delivery: The system must deliver data to the correct destination.
Accuracy: The system must transfer the data accurately, unaltered.
Timeliness: The data must arrive in a timely manner.
Jitter: There must be little jitter, that is, variations in packet arrival time.
2
Q
What is simplex communication?
A
Simplex communication is when one “station” can send and the other can receive, but not the other way around. This is very rare nowadays, but it might be like how a mouse works with a computer.
3
Q
What is half-duplex communication?
A
Half-duplex communication is when each station can send and receive, but not at the same time.
4
Q
What is full duplex communication?
A
Full duplex communication is when both stations can send and receive at the same time.
5
Q
What are the criteria for defining a network?
A
Performance, reliability, and security.
6
Q
What are the main topologies?
A
Mesh topology
Star topology
Bus topology
Ring topology
7
Q
What is a mesh topology?
A
In a mesh topology, ever device has a dedicated point-to-point link to every other device.
8
Q
What is the star topology?
A
The star topology is where each device needs only one link and one I/O port to connect it to any others, generally using a hub.
9
Q
What is the bus topology?
A
The bus topology uses one central line as a “backbone”, and then has nodes branching off of it using drop lines and taps.
10
Q
What is the ring topology?
A
The ring topology has it so that each device connects to only two other devices, using dedicated point-to-point systems.
11
Q
What are the layers of the TCP/IP model? Give an example of each.
A
Application - HTTP/FTP Transport - TCP/UDP Network - The Internet, Internet Protocol (IP), grouping of routers. DCHP Data Link - Routers, Link Layer Switch Physical - Cabling
12
Q
What are the layers of the OSI model?
A
Application Presentation Session Transport Network Data Link Physical
13
Q
How does the OSI model relate to the TCP/IP model?
A
In TCP/IP, the top three layers of OSI are combined; that is, application, presentation, and session in OSI are all combined into application in TCP/IP.
14
Q
What is the difference between a reliable vs. unreliable connection?
A
A reliable connection’s protocol has error-correcting capabilities, as well as being able to retransmit information as needed. A reliable connection generally guarantees that there will be no delay, damage, or loss of packets, and that they will be delivered in order.
15
Q
What is retransmission? What layer does it take place at?
A
Retransmission is the resending of packets which have been damaged or lost. This happens at the Transport layer.
16
Q
What is unpacking?
A
Unpacking (and packing) occur between each layer in a protocol. As a packet moves up through protocols, each protocol puts its header on it and wraps the packet, and as it comes back down, it gets unwrapped.
17
Q
Explain the difference between a digital and an analog signal?
A
An analog signal is contiguous, that is, it can be zoomed in on infinitely.
18
Q
What do the horizontal and vertical axises represent on a time domain plot?
A
Horizontal represents time, and vertical represents signal amplitude.
19
Q
What is frequency?
A
Frequency is the number of occurrences of a repeating event per unit of time.
20
Q
What is amplitude?
A
Amplitude is the measure of the change of a repeating event over a single period.
21
Q
What is phase?
A
Phase is the position of the waveform relative to time 0.
22
Q
What is attenuation?
A
Attenuation is a loss of energy, caused by resistance in the transmission medium, which generates heat, which increases resistance.
23
Q
What is peak amplitude?
A
Peak amplitude is the absolute value of a signal’s highest intensity.
24
Q
What is period?
A
Period refers to the amount of time, in seconds, that a signal needs to complete one cycle.
25
What is frequency? What unit is it commonly expressed in?
Frequency is the number of periods in one second. It is generally measured in hertz (Hz).
26
What is distortion?
Distortion is whenever a signal's shape changes. It generally is caused when composite signals have different frequencies, which may cause a difference when they arrive at the final destination. This can then cause a difference in phase.
27
What is noise?
Noise is when you receive alterations to the signal due to either heat (causing random motion of electrons), noise from electronics and motors, which act as a sending antenna, forcing the medium to act as a receiving antenna, and crosstalk, which is the result of wires being too close to one another. There is also impulse noise, which is due to a spike of excess power.
28
What is the Nyquist bit rate and how is it used?
The Nyquist bit rate formula defines the theoretical maximum bit rate.
BitRate = 2 x Bandwidth x log2L
Where L is the number of signal levels used to represent data.
29
What is the Shannon capacity, and how is it used?
The Shannon capacity is a formula that is used to determine the theoretical highest data rate for a noisy channel.
Capacity = Bandwidth x log2(1 + SNR)
SNR is the "signal-to-noise" ratio, and capacity is in bits-per-second.
30
What is line coding?
Line coding is the process of converting digital data to digital signals, that is, a series of bits to a digital signal.
31
What is block coding?
Block coding is a method for creating inherent error detecting and redundancy by taking a block of "m" bits and increasing it to "n" bits. The additional bits allow for prevention of sequential 0s and 1s, and control sequences.
32
What is scrambling?
Scrambling is a method to provide synchronization without increasing the number of bits. This is done at the same time as encoding.
Scrambling works by creating "syntax" of sorts with how ones and zeros are represented, and then signaling specific events, such as a large number of zeroes, by violating those rules in a specific way.
33
How would you calculate how many redundant bit combinations there are in a particular block coding form?
The number of usable bit combinations of the new encoding cannot be larger than the old; simply find the size of the new (2^x), and subtract the old (2^y).
34
What is NRZ?
NRZ stands for "Non-Return-to-Zero". Non-return-to-zero means that the signal does not return to zero in the middle of the bit, and means that positive voltage represents "1", and zero represents "0".
1"
35
What is NRZ-I?
NRZ-I is non-return-to-zero Invert, meaning that whether or not a bit is zero depends not on the level of the signal, but on whether or not the signal changed levels at all. In NRZ-I, it has less issue with synchronization, in that a long string of "1"s will have the signal moving constantly, making it easy to follow.
36
What is NRZ-L?
NRZ-L stands for non-return-to-zero Level. In this NRZ schema, the bit is determined directly by the level of the signal.
37
What encoding method is used for gigabit ethernet?
Four-dimensional five-level pulse amplitude modulation (4D-PAM5).
4D-PAM5 sounds complex, but simply means that it has four dimensions (four transmission mediums, wires), and has five voltage levels (-2, -1, 0, 1, 2), although one level, zero, is only used for error detection. These five (four) levels then become very similar to 8B4Q (an 8-bit word translated to a signal element with four different levels, sent over four wires, representing two bits per wire.
38
What is pulse-code-modulation (PCM)?
Pulse-code modification is the most common technique to change an analog signal to digital data (also known as digitization). PCM encoding has three processes.
1. The analog signal is modulated.
2. The sampled signal is quantized.
3. The quantized values are encoded into streams of bits.
39
What is sampling?
Sampling occurs by taking an interval of a signal and determining the signal's level at that point.
40
What is the idea sampling rate?
The ideal sampling rate was set down by Nyquist, the sampling rate must be at least twice as high as the highest frequency in the original signal.
41
What is quantization?
Quantization is a necessity born of the contiguous nature of the analog signal. Where a digital signal can be distilled down to finite points, an analog signal cannot, as it is infinite in nature. Quantization constrains the values in a sample to a discrete set.
42
What is Delta Modulation (DM)?
Delta Modulation is a simpler method to convert analog signals into digital data, compared to PCM. Delta modulation works by comparing the current signal to the previous signal, then determining the value from that. If the change is positive, a 1 is sent. If negative, a 0. This is compared to a staircase signal, which is built as a stair-stepped line, going up each time a 1 is sent, and down every time a 0 is sent.
43
What are the four types of digital to analog conversions?
Amplitude shift keying (ASK)
Frequency shift keying (FSK)
Phase shift keying (PSK)
Quadrature amplitude modulation (QAM)
44
What is shift keying?
Shift keying is the process by way a carrier signal (a high-frequency signal created as a base for information) is modulated in some way (either by modifying amplitude, frequency, or phase) in order to represent data.
45
What is amplitude shift keying?
This is done by varying the amplitude of the signal between two levels, although it can be done with more. Multiple amplitudes can be used to represent multiple combinations of bits.
46
What is frequency shift keying?
Frequency shift keying is modulating the frequency of the carrier signal in order to denote changes in value. Generally, two carrier frequencies (that is, two different set frequencies of the carrier) to denote one and zero.
47
What is phase shift keying?
Phase shift keying is done by modulating the phase from 180 degrees to zero. While the phase is at 180, the signal is one, and vice-versa. Phase shift keying is highly resistant to noise.
48
What is quadrature amplitude modulation (QAM)?
Quadrature amplitude modulation is a method of converting digital data to an analog signal by combining amplitude shift keying and phase shift keying. Where PSK has the benefit of having a resistance to noise, it's more technically difficult to pick up in phase shifts. QAM uses two carriers, one in-phase and the other quadrature, each with different amplitude levels.
49
What are the three main forms of analog-to-analog conversion?
```
Amplitude modulation (AM)
Frequency modulation (FM)
Phase modulation (PM)
```
50
What is amplitude modulation? How much bandwidth is allocated to each channel?
Amplitude modulation is a form of analog-to-analog conversion, wherein the carrier signal is modulated so that its amplitude varies with the changing amplitude of the modulating signal.
The bandwidth of AM for an audio signal is generally 5 kHz, therefore, it requires a total bandwidth of 10 kHz
51
What is frequency modulation? How much bandwidth does an FM channel take up?
Frequency modulation is an analog-to-analog conversion, wherein the frequency of the carrier signal is modulated to follow the changing voltage level (amplitude) of the modulating signal. Amplitude and phase remain constant.
The bandwidth required for audio signal in stereo is nearly 15 kHz, but the FCC allows for 200 kHz per station (to prevent overlap).
52
What is phase modulation?
Phase modulation is an analog-to-analog conversion method, wherein the phase of the carrier signal is modulated to follow the changing voltage level (amplitude) of the modulating signal. PM is basically the same as FM.
53
What's the relationship between baud rate and bit rate?
```
Data rate: n
Signal rate (baud): s
```
s = n/r
Where r has been previously defined. Just remember that they're proportional.
54
Define bit rate.
Bit rate is the number of data elements (0s and 1s) sent in 1 second.
55
Define baud rate. What else is it called?
Baud rate, also known as pulse rate, signal rate, or modulation rate, is the number of signal elements sent in 1 second.
56
Define multiplexing.
Multiplexing is the technology or techniques that allow multiple signals to be sent over a single data link.
57
What are the three main types of multiplexing?
Frequency-division multiplexing (FDM)
Time-division multiplexing (TDM)
Wavelength-division multiplexing (WDM)
58
What is frequency-division multiplexing?
Frequency-division multiplexing is a multiplexing method where multiple signals generated by a sending device are combined into a composite signal that is then transported by the link.
59
What is wave-division multiplexing?
Wave-division multiplexing is very similar to frequency-division multiplexing, in that it takes multiple signals and combines them into a composite, but in this case, it's using optical signals.
60
What is time-division multiplexing?
Time-division multiplexing is a method of multiplexing where a series of synchronized "switches" are used to alternate multiple signals over a single channel.
61
What are the two forms of time-division multiplexing, and how do they work?
The two forms of time-division multiplexing are statistical and synchronous.
Synchronous time-division multiplexing means that each input connection has an allotment in the output, even if it is not sending data.
Statistical time-division multiplexing means that the output slots are dynamically allocated based on who's sending data.
62
What are some ways that time-division multiplexing handles disparity in the input data rates?
There are three methods; Multilevel multiplexing, multiple-slot allocation, and pulse stuffing.
Multilevel multiplexing is when multiple input lines are combined to increase the total data rate to the necessary level.
Multi-slot allocation is when one higher bit-rate line is divided into two or more smaller lines.
Pulse stuffing is when dummy bits are padded to each line that's slower than the fastest to bring it up to speed.
63
Define direct sequence spread spectrum.
Direct sequence spread spectrum is a spectrum-spreading technique that replaces each bit of data with multiple bits in a specific code. This takes up more space.
64
What are bidirectional (bidi) optics?
Bidirectional optics are a way of allowing full duplex to be used on an optical fiber line, by placing the send signal on a different wavelength than the receive signal.
65
What is spectrum spreading? Why is it used?
Spectrum spreading takes place when multiple signals from different sources are combined to take advantage of large bandwidth, but it is specifically made for wireless applications, in that it adds redundancy, and adds a protective "layer" around the signal.
66
What is frequency-hopping spread spectrum?
The frequency-hopping spread spectrum technique is a spread spectrum technique that uses multiple carrier frequencies that are modulated by the source signal, and alternates between them. A psuedorandom code generator determines which frequencies are used in what order, which then loops. This prevents an intruder from intercepting much of the data, and helps to prevent jamming.
67
What is the difference between guided and unguided media?
Guided media is "physical" media, like cabling and whatnot. Unguided media is "wireless" media.
68
What are the three main types of guided media?
Twisted-pair cable
Coaxial cable
Fiber-optic cable
69
What is twisted-pair cabling?
Twisted-pair cabling consists of two conductors (generally copper), each with their own insulation, twisted together. One wire is used to carry a signal, the other is used as a "ground reference". The receiver then uses the difference between the two.
It is used all over.
70
What are the two types of twisted-pair cabling, and what are they used for?
The two types of twisted-pair cabling are shielded twisted-pair (STP) and unshielded twisted-pair (UTP). STP cabling has a metal shield between the two cables and the outer plastic layer, preventing noise and crosstalk, but is bulkier and more expensive. It is rarely used.
71
What is the most common unshielded twisted-pair connector?
The most common unshielded twisted-pair connector is the RJ45.
72
What is a coaxial cable?
A coaxial cable, or coax, is composed of multiple layers, starting with an inner conductive cable of copper (generally), surrounded by an insulator, surrounded by another conductor (to act as a shield), surrounded by another insulator, which is finally covered in plastic.
73
When is shielded twisted-pair better used than unshielded twisted-pair?
Shielded twisted-pair benefits from a greater resistance to electrical interference, and should be used in any situation where that may be a factor. Unfortunately, the cabling is bulky, which can restrict things. Shielded twisted-pair cabling is generally used in token-ring configurations.
74
What are the three types of fiber-optic connectors, and what are they used for?
The subscriber channel connector (SC) is used for cable TV.
The straight-tip connector is used to connect cable to networking devices.
The MT-RJ is a connector that is the same size as the RJ45.
75
Why is coaxial cable used for TV and internet instead of Cat5?
Unlike Cat5, which is UTP, coaxial cable is shielded and inexpensive. This allows for long-distance runs of cabling. In addition, it's very easy to make your own coaxial cabling.
76
What is baseline wandering?
Baseline wandering is what happens when a long, uninterrupted string of 1s or 0s is sent over a line, which can cause a drift in the baseline for the receiver, which then makes it difficult to correctly determine the value of the next data element.
77
What is the baseline?
The baseline is a running average of the received signal power of a line, which is used as a comparison point to determine the value of future signals.
78
What is DC component?
A DC component occurs when a digital signal's voltage level (amplitude) is constant for a period of time, allowing the spectrum to create a very low frequency.
79
A local area network (LAN) is defined by _______________.
the geometric size of the network
80
The largest geographic area a wide area network (WAN) can span is _______________.
the whole world
81
In a _____________ communication, the media needs to be shared between devices.
multipoint
82
In a _____________ communication, the media is dedicated.
point-to-point
83
The TCP/IP protocol suite consists of _______ layers.
five
84
A router is involved in ____________ layers of the TCP/IP protocol suite.
three
85
A link-layer switch is involved in ______________ layers of the TCP/IP protocol suite.
two
86
In the TCP/IP protocol suite, which of the following is an application layer protocol?
A) The User Datagram Protocol (UDP)
B) The Internet Protocol (IP)
C) The File Transfer Protocol (FTP)
D) The Transmission Control Protocol (TCP)
The File Transfer Protocol
87
In the TCP/IP protocol suite, which of the following is a transport-layer protocol?
A) The Internet Control Message Protocol (ICMP)
B) The Internet Protocol (IP)
C) The Address Resolution Protocol (ARP)
D) The Transmission Control Protocol (TCP)
The Transmission Control Protocol
88
In the TCP/IP protocol suite, which of the following is a network layer protocol?
A) The Stream Control Transmission Protocol (SCTP)
B) The Secure Shell (SSH)
C) The Internet Protocol (IP)
D) User Datagram Protocol (UDP)
The Internet Protocol
89
The transport-layer packet in the TCP/IP protocol suite is called _______________.
A segment or user datagram.
90
In the TCP/IP protocol suite, the ______ layer is responsible for moving frames from one hop (node) to the next.
data-link
91
In the TCP/IP protocol suite, the physical layer is concerned with the movement of _______ over the physical medium.
bits
92
In the TCP/IP protocol suite, a port number is the identifier at the____________.
transport layer
93
In the TCP/IP protocol suite, a logical address is the identifier at the _______________.
network layer
94
The_________ layer is responsible for the delivery of a message from one process to another.
transport
95
The Internet Protocol (IP) is ________ protocol.
an unreliable
96
The application layer in the TCP/IP protocol suite is usually considered to be the combination of ________layers in the OSI model.
Application, session, and presentation.
97
In TCP/IP, a message at the application layer is encapsulated in a packet at the ________ layer.
transport
98
In TCP/IP, a message at the transport layer is encapsulated in a packet at the ________ layer.
network
99
In TCP/IP, a message belonging to the network layer is decapsulated from a packet at the ________ layer.
data-link
100
In TCP/IP, a message belonging to the transport layer is decapsulated from a packet at the ________ layer.
data-link
101
In TCP/IP, a logical connection between an entity at the network layer can be made with another entity at the ________ layer.
network
102
In TCP/IP, a logical connection between an entity at the data-link layer can be made with another entity at the ________ layer.
data-link
103
In TCP/IP, a packet at the third layer carries data belonging to the ________ layer and the header belonging to the _________ layer.
fourth, third
104
In a frequency-domain plot, the horizontal axis measures the ________.
frequency
105
In a time-domain plot, the horizontal axis is a measure of ________.
frequency
106
_______ data are continuous and take continuous values.
Analog
107
_______ data have discrete states and take discrete values.
Digital
108
_____ signals have an infinite number of values in a time interval.
Analog
109
_______ signals can have only a limited number of values in a time interval.
Digital
110
Frequency and period are ______.
the inverse of each other
111
________is the rate of change with respect to time.
Frequency
112
_______ describes the position of the waveform relative to time 0.
Phase
113
A simple sine wave can be represented by one single spike in the _____ domain.
frequency
114
As frequency increases, the period ________.
decreases
115
________ is a type of transmission impairment in which the signal loses strength due to the resistance of the transmission medium.
Attenuation
116
________ is a type of transmission impairment in which the signal loses strength due to the different propagation speeds of each frequency that makes up the signal.
Distortion
117
________ is a type of transmission impairment in which an outside source such as crosstalk corrupts a signal.
Noise
118
When propagation speed is multiplied by propagation time, we get the ________.
the distance the bit or signal has traveled.
119
Baseband transmission of a digital signal is possible only if we have a ____ channel.
low-pass
120
If the available channel is a ____ channel, we cannot send a digital signal directly to the channel.
bandpass
121
For a ______ channel, the Nyquist bit rate formula defines the theoretical maximum bit rate.
noiseless
122
For a ______ channel, we need to use the Shannon capacity to find the maximum bit rate.
noisy
123
Polar and bipolar encoding are types of _______ coding.
line
124
___________ conversion involves three techniques: line coding, block coding, and scrambling.
Digital-to-digital
125
In ______ schemes, the voltage level oscillates between a positive and a negative value although it may remain at zero level between the two values.
polar
126
In _____, the level of the voltage determines the value of the bit.
NRZ-L
127
In ______, the change or lack of change in the level of the voltage determines the value of the bit.
NRZ-I
128
The idea of RZ and the idea of NRZ-L are combined into the ________ scheme.
Manchester
129
The idea of RZ and the idea of NRZ-I are combined into the ________ scheme.
differential Manchester
130
In Manchester and differential Manchester encoding, the transition at the middle of the bit is used for __________.
synchronization
131
In _______encoding, we use three levels: positive, zero, and negative.
bipolar
132
The _____ scheme uses data patterns of size 2 and encodes the 2-bit patterns as one signal element belonging to a four-level signal.
2B1Q
133
_______ encoding has a transition at the beginning of each 0 bit.
Differential Manchester
134
Which encoding method uses alternating positive and negative values for 1s?
Alternate mark inversion
135
Block coding can help in _______ and _________ at the receiver.
synchronization, error-detecting
136
_______ provides redundancy to ensure synchronization and inherent error detection.
Block coding
137
________ provides synchronization without increasing the number of bits.
Scrambling
138
PCM is an example of _______ conversion.
analog-to-digital
139
The most common technique to change an analog signal to digital data is called __________.
Pulse code modulation
140
The first step in PCM is ________.
sampling
141
______ finds the value of the signal amplitude for each sample; ____ finds the change from the previous sample.
Pulse code modulation, Delta modulation
