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Network Layer > Multimedia Networking > Flashcards

Multimedia Networking Flashcards

1
Q

What are the 3 application types of multimedia networking?

A
  • Streaming, stored audio, video (i.e netflix youtube)
  • Conversational voice/video over IP (i.e skype)
  • Streaming live audio and video (i.e sports events)
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2
Q

What is streaming?

A

Video or audio can begin playout before downloading entire file

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3
Q

What is meant by stored audio in multimedia networking?

A

Audio or video that is stored at a server side, can be transmitted faster than audio/video is rendered aka there is buffering at the client.

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4
Q

What is jitter?

A

Variable network delay

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5
Q

In streaming if a client’s bit rate has jitter is this an issue?

A

No as there is a buffer so the video plays out at a constant rate to the client

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6
Q

Describe how client side buffering and playout interact?

A
  • Initial fill of buffer until playout begins at t_p
  • Playout begins and continues at a constant rate
  • Buffer is filled at variable rate so buffer level varies
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7
Q

How does streaming over UDP work?

A
  • Server sends at a rate appropriate for the client
  • Sent rate = encoding rate = constant rate
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8
Q

In streaming over UDP how does congestion affect transmission rate?

A
  • It does not
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9
Q

What is a normal length for playout delay?

A

2-5 seconds

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10
Q

What is the purpose of playout delay and in what kind of multimedia use is it for?

A

It removes network jitter and is used in streaming

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11
Q

What can be an issue with the UDP used in streaming services that are not faced by TCP HTTP

A

May not be allowed through firewalls, whereas TCP may be allowed through firewalls

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12
Q

How does streaming work with HTTP? (TCP)

A
  • Multimedia file retrieved with HTTP GET
  • Send at maximum possible rate under TCP
  • Playout delay
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13
Q

Does the file rate fluctuate in HTTP streaming?

A

Yes it does, due to congestion control and retransmissions which ensure in order delivery

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14
Q

What is the difference between playout delay with UDP vs. HTTP (TCP) streaming?

A
  • TCP has larger playout delay ensures more smooth TCP delivery rate than UDP
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15
Q

In adaptive playout delay what is the equation for packet delay estimation di?

A

di = (1-a)d(i-1) + a(ri - ti)

  • di = delay estimate after ith packet
  • a = small constant e.g 0.1
  • d(i-1) = ith - 1 packet
  • ri = time received
  • ti = time sent
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16
Q

In adaptive playout delay what is the equation for average deviation of delay, vi?

A

vi = (1-b)v(i-1) + b|ri - ti - di|

-vi = average deviation of delay after ith packet
- b = small constant
- v(i-1) = previous average deviation after i-1th packet
- ri = time received
- ti = time sent
- di = packet delay estimation after ith packet

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17
Q

In adaptive playout delay what is the equation for the playout time of the first packet in a talk spurt?

A

Playout_time_i = ti + di + Kvi

  • ti = time sent
  • di = packet delay estimation after ith packet
  • vi = average deviation of packet delay value
  • K = some constant
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18
Q

What is meant by a one-size-fits all, best effort service model? and what is good about it?

A

Increasing link capacity so that congestion does not occur.
- Low complexity of network mechanisms

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19
Q

What is an issue with the one-size-fits all service model?

A
  • High deployment cost: It is wasteful because the service will not always be busy - aka waste of money
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20
Q

What is an alternative to the best effort service model?

A
  • Multiple classes of service model
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21
Q

What is the multiple classes of service model?

A
  • Partition traffic into classes
  • Network treats different classes of traffic differently
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22
Q

In the multiple classes model what 3 things should be considered to be able to maintain required QoS guarantees?

A
  • A service level agreement is necessary (SLA)
  • A policing mechanism needs to be in place
  • Flows being allowed to use another flow’s unused bandwidth whenever.(SLA
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23
Q

What do packet classification and packet marking allow routers to do?

A
  • Packet classification allows - router to treat different classes accordingly
  • Packet marking allows router to distinguish among packets belonging to different classes of traffic
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24
Q

Why are policing mechanisms necessary?

A
  • Provide a certain DEGREE of traffic isolation among classes, so that one class is not adversely affected by another traffic class that is misbehaving
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25
Q

What is call admission?

A
  • Call admission: a network may deny service if it cannot meet needs
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26
Q

What must flows do before they are allowed to join a network?

A

Declare their QoS requirements because sufficient resources will not always be available

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27
Q

What are 3 different types of scheduling policies?

A
  • FIFO (first in first out)
  • Priority queueing
  • Weighted fair queueing
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28
Q

How does priority queueing work?

A
  • Packets are sorted into high and low priority queues (waiting areas) and then packets in the higher priority queue are priorities to send out to departures through the link server
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29
Q

How does WFQ work?

A
  • Packets are classified into classes at arrival and each class gets a specified weighted amount of service each cycle
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30
Q

How can end-to-end delay be bounded with queues?

A

By bounding the queue

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31
Q

What are the 2 queue manager tasks?

A
  • Remove packets from a queue upon the request of packet scheduler
  • Discard and remark packets if queue is full or approaching saturation
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32
Q

What is an example mechanisms for discarding and remarking packets when queue is at saturation?

A
  • Random early detection with in/out (RIO)
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33
Q

What is the goal of queue management?

A
  • Proactively avoid the queue becoming congested
34
Q

What are 3 packet removal policies? And what do they mean?

A
  • Tail drop (drop arriving packet)
  • Priority (drop on a priority basis i.e lowest priority)
  • Random: (drop randomly from queue)
35
Q

What is Random Early Detection? (RED)

A
  • Process of dropping packets randomly from selected flows with some drop probability whenever the queue length exceeds given threshold
36
Q

In an example where a queue uses Random Early Detection describe how the queue operates?

A
  • If buffer average is below the minimum threshold - deduce no congestion.
  • If buffer is above maximum threshold - high congestion aka drop packets with probability 1
  • If buffer is BETWEEN min and max threshold - drop packets with probability p
37
Q

What is the difference between RED and RED In/Out (RIO) and how does RIO work?

A
  • RIO scheme assumes that an edge router has marked packets in the systems conforming to an SLA (service level agreement)
  • Packets are marked as either : non-conforming (out of profile) or conforming (in profile)
  • Packet out of profile are dropped first if a CORE ROUTER is congested
38
Q

What parameters can be used to mark different packets as in/out of profile?

A
  • things like standard vs. premium service
39
Q

What is the goal of policing mechanisms?

A

Shape traffic so it does not exceed declared parameters

40
Q

What are 3 commonly used criteria for policing mechanisms? and describe them?

A
  • Average rate : (long term) how many packets can be sent per unit time in the long run
  • Peak rate: What is the peak rate packets can be sent at
  • Burst size : Max number of packets sent consecutively
41
Q

In the token/leaky bucket scheme what does the peak rate correspond to?

A

rate that the bucket is filled up (unless the bucket is full)

42
Q

Over an interval of length t what is the maximum number of packets admitted by the leaky bucket scheme? Equation

A

Total_num = rt + b

r: peak rate that tokens fill bucket
t : length of time measured in
b: number of tokens already in bucket when time started

43
Q

What 2 things can happen when a packet is no met by a token?

A
  • Packet is dropped
  • Packet is tagged as a “naughty packet”
44
Q

What happens when you combine token/leaky bucket scheme with WFQ?

A

You can provide a guaranteed upper bound delay on the service because you can bound the queues

45
Q

If rate that packets are leaving a queue is R and bucket size is b then what is the maximum token rate, r?

A

max r = b/R

46
Q

What is the fine grained approach for internet QoS? And what is an example of this?

A
  • Providing QoS for individual applications or flows
  • I.E INTSERV (integrated services)+ RSVP
47
Q

What is the coarse grained approach for internet QoS and what is an example of this?

A
  • Provide QoS to large classes of data or aggregate traffic
  • E.G differentiated services (DS)
48
Q

What is resource reservation protocol (RSVP)

A
  • Network-level signalling protocol operating on top of IP
49
Q

Generally how does resource reservation protocol (RSVP) work?

A

Hosts request a specific QoS for a particular flow
- Routers provide requested QoS along the path(s)

50
Q

What 4 things are RSVP routers responsible for?

A
  • Dedicating requested resources (e.g bandwidth)
  • Maintaining the soft state for signal connection (i.e each flow treated individually)
  • Accept/refuse new connections based on available resources
  • Guarantee service level agreement (SLA) of existing calls
51
Q

Where can resource reservation protocol be transported (RSVP)?

A

Inside an IP packet

52
Q

What happens on sender side of resource reservation protocol? (RSVP)

A

Sender sends a message containing TSpec (flow traffic characeristics) to the receiver

53
Q

What happens on receiver side of resource reservation protocol (RSVP) ?

A
  • Looks at sender’s characteristics specification
  • Needs to know what path the packet will travel
  • Initiate the establishment of resource reservations at EACH ROUTER ON PATH
  • Reservations sent back to sender
  • If reservation CAN be made a RESV message request is passed to next router all the way back up to sender
  • RESV message contains the RSpec aka service request from networks
54
Q

What happens on receiver side of resource reservation protocol (RSVP) ?

A
  • Looks at sender’s characteristics specification
  • Needs to know what path the packet will travel
  • Initiate the establishment of resource reservations at EACH ROUTER ON PATH
  • Reservations sent back to sender
  • If reservation CAN be made a RESV message request is passed to next router all the way back up to sender
  • RESV message contains the RSpec aka service request from networks
55
Q

What are the pros of RSVP - resource reservation protocol?

A
  • It is simple to increase or decrease the level of resource allocation.
56
Q

What are the cons of resource reservation protocol (RSVP) ?

A
  • Requires each flow state information to be STORED on each particular route.
  • Each reservation needs some memory
  • Each router has to classify police and queue each flow
  • admission control decision are needed
57
Q

What is Tspec in integrated services mechanisms?

A

Describe flow’s traffic characteristics - give network info on bandwidth requirements of incoming flow

58
Q

What is RSpec in integrated services mechanisms?

A

Describe service request - request for bound delay etc.

59
Q

What is call admission control in integrated service mechanisms?

A
  • Looks at TSpec and RSpec and decides on a per-flow basis if the service can be provided.
60
Q

What is resource reservation?

A
  • Bandwidth and buffers are reserved for a data flow
61
Q

What is traffic policing in integrated services mechanisms?

A
  • Per-packet decisions to ensure that all flows conform to their TSPec
62
Q

General description of INSERV (integrated service) ?

A
  • Uses RSVP (resource reservation protocol)
    and
  • Per flow QoS-sensitive scheduling
    (once RSVP reply is sent then management of queues begins)
63
Q

What is difference between differentiated service (DS) and integrated service models (INSERV)?

A
  • DS model is a simpler and more scalable solution
  • Per flow service is replaced with per aggregate service
  • Complex processing is moved from the core routers to edge routers
64
Q

How is differentiated service (DS) transmitted?

A

In an IPv6 datagram, there is a DS field which contains a packets class, so the DS field is used to identify per hop behaviour I.E how a router will treat a packet depending on the class it’s from

65
Q

Does a differentiated service (DS) need a service level agreement?

A

Yes. Customer wishing to receive a DS must first have a SLA

66
Q

What does a service level agreement (SLA) include for a differentiated service (DS)? And what is this?

A

It includes a traffic conditioning agreement (TCA) - it defines the nature of the various traffic classes and services

67
Q

In a differentiated service (DS) what is an edge router responsible for?

A
  • Per-flow aggregate traffic management
  • To ensure traffic conformance in respect to TCA (traffic conditioning agreement at the edge-router)
  • Marks packets as either in-profile or out-profile (e.g using the leaky bucket)
68
Q

In a differentiated service (DS) what is a core router responsible for?

A
  • Per class traffic management
  • Queueing and scheduling based on marking at edge (no soft knowledge)
  • Preference is given to in-profile packets over out-profile ones
69
Q

What is meant by per-hop behaviour? PHB

A
  • Routers class differentiation
70
Q

What happens when an edge router in DS does traffic classification?

A

Directs a packet into various output based on content of packet header (DS, ID number, dest address etc.)

71
Q

What is the role of an edge router as a traffic conditioner in differentiated services?

A

Metering, marking, shaping and dropping packets

72
Q

What are the different ways that packets can be marked by an edge-router used in differentiated services?

A
  • Class-based marking: packets from different classes marked differently
  • Intra-class marking: conforming the (in-profile) portion of flow marked differently than non-conforming (out-profile) one
73
Q

What are the effects of PHBs in core-routers in differentiated services?

A
  • Per hop behaviour
  • PHB result in a different measurable forwarding performance behaviour (each forwarding strat has diff performance)
  • PHB doesn’t specify what mechanisms to use to ensure required PHB performance behaviour
74
Q

What are the 3 different classes of PHB forwarding?

A
  • Expedite forwarding
  • Assured forwarding
  • Default PHB
75
Q

What is expedite forwarding PHB?

A
  • Low-loss, low-latency, low-jitter (not much randomness), assured bandwidth end to end services
  • Limited by speed link of router
  • Can be implemented using priority queueing or WFQ
76
Q

What is assured forwarding PHB?

A
  • Delivers the aggregate traffic with high assurance as long as the traffic does not exceed the traffic profile
  • Not-intended for low-latency , low-jitter
77
Q

What is default PHB?

A

Best effort treatement

78
Q

WWhat is link virtualisation?

A

Viewing the internet as a logical link connecting IP routers

79
Q

What is multiprotocol label switching? (MPLS)

A
  • Integrates layer 2 switching with layer 3 switching
80
Q

What is key feature in a label switching router (LSR)?

A
  • Key feature is separation of CONTROL PLANE (sets up routes) and FORWARDING PLANE (carries information)
81
Q

Why are multiprotocol label switching routers good? (MPLS)

A
  • Improve forwarding performance (simplified lookup)
  • Improve scalability (label stacking and merging)
  • Provide traffic engineering (through explicit routing)

Network Layer (6 decks)

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