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CS4105 Advanced Communication Networks and Systems > Lecture 8: 19th November 2019 > Flashcards

Lecture 8: 19th November 2019 Flashcards

Adaptive streaming for multimedia (esp video)

1
Q

What is adaptive streaming?

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2
Q

Why is video streaming omportant?

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3
Q

What is the problem with a single video stream for all devices?

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4
Q

What is the end-to-end workflow path for video streams?

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5
Q

How should streams of stored video files work?

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6
Q

What does streaming mean?

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7
Q

What does streaming mean with regard to sending video files?

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8
Q

What are the challenges of streaming stored video files?

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9
Q

How do stored video streams differ from their ideal scenario in practice?

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10
Q

How is network delay and jitter compensated for?

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11
Q

What is jitter?

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12
Q

How does client-side buffering work?

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13
Q

What are the mathematical parameters of client-side buffering?

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14
Q

How does client-side buffering work, with respect to its mathematical parameters?

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15
Q

What is the average fill rate of a client-side buffer?

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16
Q

What is the playout rate of a client-side buffer?

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17
Q

What is the initial playout delay tradeoff?

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18
Q

How does multimedia streaming work with UDP?

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19
Q

How does multimedia streaming work with HTTP?

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20
Q

What are the issues with HTTP-based streaming in the application layer?

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21
Q

What are the issues with HTTP-based streaming in the networks and systems?

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22
Q

Why may there be a tradeoff between quality and buffering?

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23
Q

How can we avoid a tradeoff between quality and buffering?

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24
Q

What are the three steps by which we can avoid a tradeoff between quality and buffering?

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25
Q

How does encoding work when avoiding a tradeoff between quality and buffering?

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26
Q

What is a bitrate ladder?

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27
Q

How does a bitreate ladder work?

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28
Q

How does video encoding work with bitrate ladders?

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29
Q

What is a manifest file?

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30
Q

How are manifest files used with video encoding?

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31
Q

What is a CDN?

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32
Q

What is rate adaptation?

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33
Q

What do servers and clients have to do to perform rate adaptation?

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34
Q

What is adaptive streaming known as over HTTP?

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35
Q

What is HAS?

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36
Q

What is DASH?

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37
Q

What measures allow you to perform rate adaptation?

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38
Q

What is capacity-based rate adaptation?

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39
Q

How does capacity-based rate adaptation work?

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40
Q

How easy is it to estimate a video flow’s capacity?

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41
Q

How consistent is the end-to-end throughput of video flows using capacity-based rate adaptation?

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42
Q

What is buffer-based rate adaptation?

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43
Q

How does buffer-based rate adaptation work?

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44
Q

How are the rate of the next chunk to be sent and buffer occupancy related in video flows using buffer-based rate adaptation?

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45
Q

When is a video flow using buffer-based rate adaptation safe from unnecessary rebuffering?

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46
Q

What is fairness?

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47
Q

What is QoE?

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48
Q

What is QoE fairness?

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49
Q

What is QoE fairness in video streams?

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50
Q

Why is it difficult to quantify fairness?

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51
Q

Why may rate adaptation remove unfairness in video streams unfairness?

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52
Q

Why does rate adaptation not remove unfairness in video streams in practice?

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53
Q

Which QoS measures suffer when there are multiple competing video streams on a network?

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54
Q

What is the difference between the bitrate and transmission rate of a video stream?

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55
Q

Why can rate adaptation lead to unfairness with competing video streams?

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56
Q

What are the contributing causes of unfairness with cmpeting video streams?

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57
Q

What is the fundamental root cause of unfairness with cmpeting video streams?

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58
Q

What is feedback control?

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59
Q

Why is the transmission rate of TCP like a sawtooth?

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60
Q

What is AIMD in TCP?

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61
Q

What are the properties of AIMD in TCP?

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62
Q

What is the feedback control loop in the network layer in TCP?

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63
Q

How does the feedback control loop in the network layer in TCP work?

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64
Q

What is the feedback control loop between the network and application in TCP?

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65
Q

How does the feedback control loop between the network and application in TCP work?

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66
Q

Why is bitrate not a good measure for fairness?

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67
Q

How are traditional TCP flows and media streaming flows over TCP different?

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68
Q

What are some metrics by which you can assess the quality of a video? Which are objective? Which are subjective?

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69
Q

What do metrics to assess video quality not consider?

A

screen size or resolution, showing it is not important

70
Q

What is bandwidth utility?

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71
Q

How do you find bandwidth utility?

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72
Q

How may bandwidth utility be applied to find video stream fairness?

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73
Q

What two measures of fairness can you find using the max-min principle?

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74
Q

How can you find bitrate max-min fairness?

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75
Q

How can you find utility max-min fairness?

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76
Q

When is the quality of video on a device optimal?

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77
Q

What is pixel density?

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78
Q

What is the PPI measure?

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79
Q

What is the normalised PPI measure?

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80
Q

How can QoE be quantified in a way that includes the relative resolution of the video vs the screen?

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81
Q

What is SSIM?

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82
Q

What is bandwidth utility?

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83
Q

How does the bandwidth available to a device improve the utility/QoE of its video stream flows?

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84
Q

How do you find SSIM - process not formula?

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85
Q

How can bandwidth-utility and QoE metrics implement fairness?

A

Find bandwidth on each device for a utility defined by a QoE metric value and then give them to all devices. Choose max obtainable utility value?

86
Q

What is VHS?

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87
Q

How does the use of VHS affect the bitrate of competing video stream flows?

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88
Q

How does the use of VHS affect the bitrate of competing batch video download streams?

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89
Q

What is CDF?

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90
Q

What is JFI?

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91
Q

How does the CDF of video stream flows change as JFI increases with and without VHS?

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92
Q

How does the CDF of video stream flows change as link utilisation increases with and without VHS?

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93
Q

How does VHS affect the bitrate instability of video stream flows?

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94
Q

How does the CDF of batch video download flows change as JFI increases with and without VHS?

A

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95
Q

How does the CDF of batch video download flows change as link utilisation increases with and without VHS?

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96
Q

How does VHS affect the bitrate instability of batch video download flows?

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97
Q

Why does the use of HTTPS/encrypted communications affect adaptive video streaming?

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98
Q

What is the difference between session-rate and experience equality?

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99
Q

Where should QoS and QoE information generated by client hosts be sent? How should it be handled?

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100
Q

Can adaptive video streaming be implemented over HTTPS with client interaction? Why?

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101
Q

What is cDVD?

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102
Q

What is the architecture of cDVD?

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103
Q

How does cDVD work?

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104
Q

How does cDVD affect video stream bitrates?

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105
Q

Why does QoE fairness matter?

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106
Q

What is DASH-S?

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107
Q

What are the challenges with implementing DASH-S?

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108
Q

How may DASH-S be implemented?

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109
Q

What are the key challenges of adaptive video streaming?

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110
Q

How could video stream flow fairness return to the TCP-based rate equality model?

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111
Q

Why is a fixed network delay unrealistic with video stream flows?

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112
Q

How may network conditions change the playout buffer occupancy?

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113
Q

What is a common video segment size?

A

4 seconds

114
Q

When should video stream flows start playing?

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115
Q

Where is Netflix’s CDN present? How?

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116
Q

Why is the quality of video streams initially poor(er)?

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117
Q

Which host in a video flow controls it? How?

A

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118
Q

How can you crudely estimate throughput from sending a single video segment? What does it not account for?

A

just assume throughput for all same as just that one

multi path
changing network conditions
changing bitrate

119
Q

What is the priority in terms of video stream flows - quality or a lack of buffering?

A

lack of buffering

120
Q

What’s the overall priority of video stream flows?

A

To deliver video sections in less than the time taken to send them. Segments usually of playback time 4s.

121
Q

How can you estimate capacity from throughput?

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122
Q

How does receiver buffer occupancy influence the sending video bitrate?

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123
Q

Why are the increases in bitrate for increases in buffer occupancy non-linear?

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124
Q

How are video segments distributed into HTTP get requests?

A

Each one forms a separate GET request.

125
Q

How do clients request video segments to arrive more rapidly or slowly or of a different bitrate?

A

In HTTP GET request parameters.

126
Q

How may a large increase in the capacity of a link affect the existing buffered segments in the receiver?

A

They could be replaced with equivalent higher-quality segments.

127
Q

Why does an equal bitrate of video streams not imply fairness between them?

A

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128
Q

What is feedback loop?

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129
Q

Why is TCP’s ack response system a feedback loop?

A

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130
Q

Why is there a delay between the bottleneck throughput changing and the bitrate of a video flow increasing?

A

rec buffer lol

131
Q

What components’ feedback control loops affect the bitrate of video stream flows, and in what order?

A

application client then TCP (sawtooth)

132
Q

What do gaps in feedback control graphs indicate with TCP-based video stream flows?

A

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133
Q

Why can simultaneous changes from the feedback control systems in the application and network layers cause issues?

A

They interfere and can make the flow performance worse rather than better

134
Q

Why do VPNs use UDP?

A

TCP in connection to gateway and gateway-gateway would casuse 2x retransmissions in the event of loss

135
Q

How can you define the utility of data by each bit?

A

“value” of each bit to the user

136
Q

How can the viewing device or its properties be known?

A

HTTP headers or app-level logic

137
Q

What is bitrate instability?

A

A measure of how much bitrate is chaging.

138
Q

Why are QoS mechanisms hard to implement over encrypted channels?

A

Can’t do DPI on headers as they’re encrypted

139
Q

Why may client interaction be a good way of implementing adaptive video streaming?

A

Only they can know (estimate) QoE

140
Q

What does VHS stand for?

A

Video Home Sharper

141
Q

What does cDVD stand for?

A

Client-Driven Video Delivery

142
Q

What do max-min algorithms do in general?

A

Maximise the minimum anyone recieves of some metric or resource

143
Q

Do max-min algorithms scale?

A

no

144
Q

Can max-min algorithms be implemented for QoE QoS in the network core? Why?

A

No. Not scalable.

The exception to the latter may be in mobile providers. This is because they have a small number of gateways to allow for charging and resource reservations

145
Q

What does fairness not account for?

A

Users not being fair in their usage; it only considers resource fairness to each host/flow

CS4105 Advanced Communication Networks and Systems (18 decks)

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