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Communication Networks > Multimedia Networks > Flashcards

Multimedia Networks Flashcards

1
Q

What are the 3 application types of multimedia networking?

A
  1. streaming stored
    audio/video
  2. Conversational voice/video
    over IP
  3. streaming live audio/video
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2
Q

What is client-side buffering?

A
  1. initial fill of buffer
  2. playout begins (at t_p)
  3. buffer fill level varies over
    time (fill rate x(t) varies and
    playout rate r is constant)
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3
Q

Why is HTTP used for streaming multimedia?

A
  • file retrieved via HTTP GET
  • send at max rate under TCP
  • fill rate fluctuates due to TCP
    congestion
  • larger playout delay = smooth
    TCP delivery rate
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4
Q

Why is UDP used for streaming multimedia?

A
  • server sends at rate
    appropriate for client
  • short payout delay to remove
    network jitter
  • error recovery at application
    level
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5
Q

What is the equation for playout time for first packet in talk spurt?

A

playout time_i = t_i +d_i + Kdv_i

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6
Q

how does a one size fits all service model work?

A

increase link capacity so congestion doesn’t occur

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7
Q

what are the disadvantages of a one-size fits all service model?

A
  • low complexity of network
    mechanisms
  • high deployment costs
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8
Q

What is a multiple classes of service model?

A
  • partition traffic into classes
  • network treats different
    classes differently
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9
Q

What are the 4 principle QoS guarantees for network mechanisms

A

Service Level Agreement
Policing mechanism
Unused bandwidth
Call admission

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10
Q

Why do we need an SLA (service level agreement)?

A

packet classification = router treat different traffic classes accordingly

packet marking = router can distinguish packets belong to different classes

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11
Q

Why do we need a policing mechanism?

A
  • provide degree of traffic isolation among classes
  • one class not adversely affected by another that’s misbehaving
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12
Q

Why do we need an unused bandwidth mechanism?

A
  • whilst providing isolation between flows, want to use resources efficiently
  • flows allow use of another flow’s unused bandwidth at any time
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13
Q

Why do we need call admission?

A
  • sufficient resources not always available
  • before accepting new call, flows declare QoS requirements
  • network can deny if cannot meet needs
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14
Q

What is priority queuing?

A

multiple queues to classify as high/low priority

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15
Q

What is weighted fair queueing?

A
  • generalized round robin
  • each class gets weighted amount of service in each cycle
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16
Q

What are the tasks of queue management?

A
  1. remove packets from a queue on request from packet scheduler
  2. discard/remark packets if queue full/saturated
    - proactively avoid queue becoming congested
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17
Q

What is packet removal/discard policy and what are some examples?

A

if packet arrives to full queue what do we do?
- tail drop = drop arriving packet
- priority = drop on priority basis
- random = drop randomly

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18
Q

What is random early detection (RED)?

A
  • drop packets randomly from selected flows
  • when queue length exceeds threshold
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19
Q

What is a 2 queue length threshold?

A
  • if buffer average below min threshold, no congestion
  • if buffer above max threshold, drop packets with p= 1
  • if buffer between min and max, drop packets with p = p
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20
Q

What is random early detection with in/out (RIO)?

A
  • assumes edge router marking of packets conforming to SLA
  • conforming packets in profile
  • non-conforming out of profile
  • out of profile packets dropped first if core router has congestion
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21
Q

What is the goal of a policing mechanism?

A

shape traffic so it doesn’t exceed declared/agreed parameters

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22
Q

What are the 3 commonly used criteria for policing mechanisms?

A
  1. Average rate: packets sent per unit time
  2. Peak rate
  3. Burst size: max no of packets sent consecutively
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23
Q

What do combine token/leaky bucket and weighted fair queueing provide?

A

Upper bound on delay

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24
Q

What are the 2 approaches on internet quality of service?

A

Fina grained approach
- provide QoS for individual applications or flows

Coarse grained approach
- provide QoS to large classes of data or aggregate traffic

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25
Q

What is resource reservation protocol (RSVP)?

A

network-level signalling protocol operating on top of IP

26
Q

How does RSVP work?

A
  • host requests specific QoS for particular flow
  • routers provide requested QoS along paths
27
Q

What are RSVP routers responsible for?e

A
  • dedicate requested resources
  • maintain soft state for signalled connection
  • accept/refuse new connections based on available resources
  • guarantee service level agreement of existing calls
28
Q

How does the sender work is RSVP?

A

send message containing TSpec to receiver

29
Q

What is TSpec?

A

flow traffic characteristics

30
Q

How does the receiver work in RSVP?

A
  • looks at sender traffic specifications TSpec
  • needs to know path of packet
  • initiate establishment of resource reservations at each router on the path
31
Q

Where are reservations sent in RSVP?

A

back to sender

  • if reservation can be made, RESV message request to next rout
32
Q

What is an RSEV message?

A

message containing RSpec

33
Q

What is RSpec?

A

service request from networks

34
Q

What are the pros/cons of RSVP?

A

pro:
- simple to increase/decrease
level of resource allocation

con:
- required for each flow state
info to be stored on
particular route
- each reservation needs
memory
- routers have to classify,
police and queue each flow
- need admission control decisions

35
Q

What is call admission control?

A

looks at TSpec and RSpec and decides per flow if service can be provided

36
Q

What is resource reservation for RSVP?

A

bandwidth and buffers reserved for data flow

37
Q

How does traffic policing work in RSVP?

A

per-packet decision to ensure all flows conform to TSpec’s

38
Q

What is the differentiated services model?

A
  • simple and more scalable
  • per flow service replaced with per aggregate service
  • complex processing moved form core to edge of network
  • allocates resources to small number of traffic classes
39
Q

What is the Differentiated Service (DS) field used for?

A

identify per hop behaviour at each node

40
Q

What is required for DS?

A
  • service level agreement
41
Q

What does a service level agreement (SLA) include?

A
  • traffic conditioning agreement (TCA)
42
Q

What is a traffic conditioning agreement (TCA)?

A

defines nature of various traffic classes and services

43
Q

How does DS work for the edge router?

A
  • per-flow (aggregate) traffic management
  • marks packets as in-profile and out of profile
44
Q

How does DS work for the core router?

A
  • per class traffic management
  • queueing and scheduling based on marking at edge
  • preference to in-profile packets
45
Q

What are the 2 ways of ensuring traffic conformance for TCA at the edge router?

A

Traffic classification
Traffic conditioner

46
Q

What is traffic classification in regards to TCA?

A

direct packets into various output based on content on packet headers

47
Q

What is traffic conditioning in regards to TCA?

A

metering, marking, shaping and dropping

48
Q

What is packet marking?

A
  • packet marking at edge based on per-flow profile
49
Q

What are the 2 types of packet marking and how do they work?

A

class-based marking: packets of different classes marked differently

intra-class marking: conforming (in-profile) portion of flow marked differently than non-conforming

50
Q

How does forwarding per-hop behaviour work?

A
  • individual routers class differentiation are called PHB
  • PHS results in different measurable forwarding performance behaviour
  • doesn’t specify what mechanisms to use to ensure required PHB performance
51
Q

What is expedite forwarding PHB?

A

low loss
low latency
low jitter
assured bandwidth
end to end services

52
Q

What is assured forwarding PHB?

A

delivers aggregate traffic with high assurance as long as traffic doesn’t exceed traffic profile

  • not intended for low latency/low jitter
53
Q

What is expedite forwarding PHB limited by?

A

link speed of router

54
Q

What is expedite forwarding PHB implemented by?

A

using priority/weighted fair queueing

55
Q

How does assured forwarding PHB work with queue management?

A

AF has root in RIO queue management

56
Q

What is multiprotocol label switching (MPLS)?

A
  • viewed by internet as logical link connecting IP routers
  • integrates layer 2 switching with layer 3 routing
  • separation of control plane and forwarding plane
57
Q

What does the forwarding plane do?

A

carries info

58
Q

What does the control plane do?

A

set up routes

59
Q

What so MPLS switching routers do?

A
  • improve forwarding performance using simplified lookup process
  • improve scalability using label stacking and merging
  • provide traffic engineering via efficient explicit routing
60
Q

What are some remarks on MPLS?

A
  • doesn’t define another QoS architecture
  • uses DiffServ architecture
  • processing of aggregate traffic only
  • DSCP field not available to MPLS LSR
  • mapping needed to map DSCP field into EXP field

Communication Networks (8 decks)

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