Multimedia

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Multimedia

• Quality of Service (QoS)

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Contents

• Why Quality of Service (QoS)?
• Introduction
• Streaming
• Multimedia on the Internet
• Is Internet Real-time?
• Internet QoS Models

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Why Quality of Service (QoS)?

• Definition QoS is the concept for specifying
  how good the offered services are.
• Concept
• Quality of service is a concept based on the
  statement that not all applications need the same
  performance from the system/network over which
  they run.
• Thus, applications may indicate their specific
  requirements to the network, including cost,
  before they actually start transmitting data.

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Introduction

• QoS Parameters
• Why is QoS Hard?
• QoS Layering and Mapping

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Major Parameters Defining QoS

• Throughput the total amount of work completed
  during a specific time interval.
• Delay the elapsed time from when a request is
  first submitted to when the desired result is
  produced.
• Jitter the delays that occur during playback
  of a stream.
• Reliability how errors are handled during
  transmission and processing of continuous media.

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Delay in packet-switched networks (1)

• nodal processing
• check bit errors
• determine output link
• queuing
• time waiting at output link for transmission
• depends on congestion level of router

• Packets experience delay on end-to-end path
• four sources of delay at each hop

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Delay in packet-switched networks (2)

• Propagation delay
• d length of physical link
• s propagation speed in medium (2x108 m/sec)
• propagation delay d/s

• Transmission delay
• R link bandwidth (bps)
• L packet length (bits)
• time to send bits into link L/R

Note s and R are very different quantities!
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Communication QoS Parameters

• Average Throughput (bit rate, bandwidth)
• Burstiness (average to peak ratio)
• Minimum/Maximum transit (delay)
• Important for response time and RT perception
• Maximum Jitter (delay variance),
• Important for synchronization
• Reliability
• Acceptable bit error rate
• Acceptable packet error rate

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ExampleVC QoS
Throughput
Loss
Jitter
Measured QoS Parameters
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Application QoS Parameters

• Synchronization
• Orchestration
• Multicast Delivery
• Protection/Security

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Why is QoS Hard? (1)

• 1. End-to-End vs. Local Node (control)

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Possible Network Bottlenecks
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Why is QoS Hard? (2)

• 1. End-to-End vs. Local Node (control)
• 2. Global vs. Specific QoS (application)

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Global/Standard Channel Types
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Why is QoS Hard? (3)

• 1. End-to-End vs. Local Node (control)
• 2. Global vs. Specific QoS (application)
• 3. Uniform vs. Distance Dependant

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Why is QoS Hard? (4)

• 1. End-to-End vs. Local Node (control)
• 2. Global vs. Specific QoS (application)
• 3. Uniform vs. Distance Dependant
• 4. Higher-Level vs. Lower-Level
  (user/application/OS/network/device)

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QoS Layering
Users
Application
System (OS)
Network
Devices
Disk, MM devices
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QoS Mapping Example
Interface Specification
TYPE VideoSource INTERFACE BEGIN GetVideo
OPERATION RETURNS VideoFrame WITH QOS
StandardVideo END.
Orchestration
Delivery rate 25 frames/sec Permissible jitter
10 ms Synch interval 1 second
Transport
Burst size 100 Kbps Burst rate 100 per
sec Delay 1 sec Jitter 20 ms Priority 10 Error
profile FEC Error rate 2
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QoS for Networked Applications
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QoS Traffic Topics (1)

• Routing
• Unicast (multi-hop network)
• Multicast
• Congestion Control
• Traffic Topics
• Admission Control (on-line)
• Systems often use an admission control algorithm
  that admits a request for a service only if the
  server has sufficient resources to satisfy the
  request.

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QoS Traffic Topics (2)

• Traffic Classes (varied) priorities
• Traffic Control (nodal)
• packet classification/scheduling
• Traffic Shaping (per session)
• Traffic Monitoring
• Traffic Policing

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Streaming and QoS

• With text data, the effect that time has on
  correctness is of little consequence.
• However, audio and video are time-dependent data
  streams if the timing is off, the resulting
  output from the system will be incorrect.
• Time-dependent information known as continuous
  media communications
• Example voice PCM 1/44100 sec intervals on
  playback.
• Example video 30 frames per second (30-40ms per
  image).
• KEY MESSAGE Timing is crucial!

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Transmission Modes

• Asynchronous transmission mode the data stream
  is transmitted in order, but theres no timing
  constraints placed on the actual delivery (e.g.,
  File Transfer).
• Synchronous transmission mode the maximum
  end-to-end delay is defined (but data can travel
  faster).
• Isochronous transmission mode data transferred
  on time theres a maximum and minimum
  end-to-end delay (known as bounded jitter).
• Known as streams isochronous transmission
  mode is very useful for multimedia systems.

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Two Types of Streams

• Simple Streams one single sequence of data, for
  example voice.
• Complex Streams several sequences of data
  (sub-streams) that are related by time. Think
  of a lip-synchronized movie, with sound and
  pictures, together with sub-titles
• This leads to data synchronization problems not
  at all easy to deal with.

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Components of a Stream

• Two parts a source and a sink.
• The source and/or the sink may be a networked
  process (a) or an actual end-device (b).

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End-device to End-device Streams
2-35.2

• Setting up a stream directly between two devices
  i.e., no inter-networked processes.

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Multi-party Data Streams

• An example of multicasting a stream to several
  receivers. This is multiparty communications
  different delivery transfer rates may be
  required by different end-devices.

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Stream Synchronization

• A key question is
• Where does the synchronization occur?
• On the sending side?
• On the receiving side?
• Think about the advantages/disadvantages of each

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Synchronization Mechanisms (1)

• The principle of explicit synchronization on the
  level data units

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Synchronization Mechanisms (2)

• The principle of synchronization as supported by
  high-level interfaces

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Streams and QoS (1)

• Definition ensuring that the temporal
  relationships in the stream can be preserved.
• QoS is all about three things
• Timeliness
• Volume
• Reliability
• But, how is QoS actually specified?
• Unfortunately, most technologies do their own
  thing.

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Data Stream

• A general architecture for streaming stored
  multimedia data over a network.

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Streams and QoS (2)

• Properties for Quality of Service (QoS)
• The required bit rate at which data should be
  transported.
• The maximum delay until a session has been set
  up.
• The maximum end-to-end delay.
• The maximum delay variance, or jitter.
• The maximum round-trip delay.

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Enforcing QoS (1)

• Using a buffer to reduce jitter

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Enforcing QoS (2)

• The effect of packet loss in (a) non interleaved
  transmission and (b) interleaved transmission