QoS Requirements of Multimedia Applications

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QoS Requirements of Multimedia Applications

• Brett Berliner
• Brian Clark
• Albert Hartono

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Introduction

• What does QoS mean?
• Quality of Service
• probability of the network/protocol meeting a
  given traffic contract.
• Who negotiates this contract?
• SLA (Service Level Agreement)
• Usually done by prioritizing traffic
• Sender and receiver
• Mutual agreement
• Improves reliability of contract by having both
  ends agree
• Like with any contract negotiation is the key

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Introduction Cont

• Generally not used for most traffic in internet
• Usually things are not dependant on time domain
• Web browsing, e-mail, ftp, etc.
• TCP takes care of this for us
• Mainly used for multimedia applications
• Time is of the essence
• Video, voice, games, etc.
• Always a trade-off
• Higher QoS (higher quality) -gt More resources
• Users of SLA must be fair and honest
• Five basic parameters

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Dropped Packets

• A router must drop an incoming packet because
  buffer is full
• No perfect solution to this problem
• Some, none, or all might get dropped
• Impossible to determine in advance
• How to recover?
• Receiver must request packets to be sent again
• Causes severe delay
• Sometimes not worth it to request packet again

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Delay

• Queuing
• Time spent waiting in a queue at a router
• Depends on congestion in the network
• Usually in milliseconds
• Processing Delay (usually caused by software)
• At different layers, data must be processed
• Usually in microseconds
• Propagation Delay
• Time for data to travel from A-gtB
• Depends on distance, usually in milliseconds
• Transmission Delay
• Depends on bandwidth and length of message,
  usually in microseconds

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Jitter

• A lack of synchronization
• Caused by different delays in packets
• Result of packets taking different routes
• Directly related to congestion
• Extreme jitter can lead to out-of-order delivery
• Packets need to be re-ordered at receiver
• Sometimes this is impossible due to time
  constraints

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Error

• Packets do not always arrive in the exact state
  they were sent out in
• Can be misdirected (sent to wrong destination)
• Can get combined together by accident
• Can have bit(s) flipped.
• Receiver must request information to be sent
  again
• Many times this is not practical for multimedia
  applications

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Bandwidth

• Amount of data that can be sent over a connection
  in a given amount of time
• Commonly measured in bits/second
• kbps or mbps instead
• Sometimes a given connection is simply physically
  unable to fulfill a SLA
• Imagine trying to stream HDTV quality video over
  a 14.4 kbps modem

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What Happens When QoS Fails?

• VoIP Example
• Delays followed by effect
• lt 100 150 ms Delay is not detectable by humans
• 150 250 ms Acceptable quality, but delay and
  hesitation is noticeable
• gt 250 300 ms Unacceptable. Normal
  conversation is impossible
• Jitter followed by effect
• lt 40 ms Jitter is not detectable
• 40-75 ms Good quality, but occasional jumble is
  noticeable
• gt 75 ms Unacceptable. Too much jumble to carry
  a conversation

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What Happens When QoS Fails?

• Video Example
• Out of sync image is a result of motion
  prediction. Result of loss of a P or B frame
• Missing image parts result of a missing I frame

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Summary of QoS Requirements For Specific
Applications
Application Dropped Packets Delay Jitter Bandwidth
VoIP lt 3 packet loss ratio 150 200 ms lt 30 ms 21 320 kbps
High Quality Audio Video lt 1 packet loss ratio 150 ms lt 30 ms 768 kbps 20 overhead 921 kbps
Remote Visualization None none 700 Mbps
Internet Gaming none 150 ms none 56 kbps
Web Browsing none 2 sec is preferred, 4 sec is acceptable none 10 kbps
Streaming Video lt 5 4-5 seconds n/a Varies with encoding format
Uncompressed HDTV 1.5 Gbps
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Whos Responsibility Is It?

• Routers dont know typically know what the data
  is
• Thus, it requires a lot of overhead to allow the
  routers to interpret the data
• The encoding and decoding of the data in the
  sender and the receiver(s) makes them a prime
  target
• This is where most of the focus of ensuring that
  QoS requirements are met lies

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Basic Types of QoS Technologies

• Congestion/Traffic Control
• Examples RED, FRED, Droptail
• Resource Management
• Examples IntServ, DiffServ
• Queuing/Buffering
• Priority Queuing, FRTS

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Congestion Control Methods

• RED/FRED
• Droptail
• Bucketing
• QoS/BGP

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Congestion Control Methods (cont.)

• RED, FRED and Droptail Methods
• Already discussed extensively in class
• Methods to improve congestion, but like all
  methods, have their own drawbacks and benefits
• Important to note that these methods only help
  improve QoS on a very high level. They improve
  congestion and traffic, which helps the entire
  internet, not just QoS issues.

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Congestion Control Methods (cont.)

• QoS / BGP (QoS Policy Propagation via Border
  Gateway Protocol)
• BGP is the core routing protocol of the internet
• Instead of using BGP solely to determine where to
  send the packets, build on top of BGP to classify
  the type of packets being sent
• Allows other methods, like queuing or scheduling,
  to be used in conjunction to ensure QoS
  requirements are met

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Resource Management Methods

• IntServ (Integrated Services)
• A fine grained QoS system
• Individual applications must make indvidual
  reservations of resources
• By making reservations, the application is
  guaranteed a certain level of service from
  best effort to 100 guarantee, and everything
  in between
• Uses RSVP (Resource ReSerVation Protocol) to help
  determine what resources to allocate where.

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Resource Management Methods (cont.)

• DiffServ (Differentiated Services)
• Much more coarse QoS system
• Reservations are done in bulk, usually from a
  single source (such as a university or a single
  ISP)
• Policing of data is done completely at DiffServ
  clouds (individual systems of routers)
• Data with highest priority is given highest
  priority, within clouds only

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Resource Management Methods (cont.)

• Weaknesses of these methods
• IntServ
• Similar to FRED, lots of data must be stored.
  Thus, hard to scale for the entire internet
• DiffServ
• Not a good system for most links.
• Since the traffic comes in very large chunks
  (e.g., all traffic from OSU as well as all from
  Otterbein), there is likely to be relatively
  steady traffic.
• If packets need to be dropped, more bandwidth is
  needed to fix the problem in most cases.

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Queuing/Buffering Methods

• FRTS (Frame Relay Traffic Shaping)
• Excess traffic is delayed using a buffer or a
  queue
• Idea is to shape the flows traffic, usually when
  the data rate of the source is higher than
  expected.
• Works very well with a large queue or a small
  scale. If the queue is too small, or FRTS is run
  on a large scale (e.g., the whole internet), a
  queue management algorithm would be necessary.

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Queuing/Buffering Methods (cont.)

• CSFQ (Core Stateless Fair Queuing)
• First step edge nodes estimate the incoming
  rate of packets being sent, then uses that as a
  label for each of that flows packet
• Next all nodes (including edge) repeatedly
  estimate the fair rate from the outgoing link.
  Upon arrival, the probability the packet will be
  forwarded is calculated, based on the previously
  calculated probability, as well as the previous
  label.
• When that packet is forwarded, it is sent with
  that probability, and the label is replaced with
  the smaller value between its previous value and
  the fair rate.

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Queuing/Buffering Methods (cont.)

• Advantages of CSFQ
• Per flow management is performed, allowing each
  flow to get a fair rate
• Stateless (less information stored, the better)
• Disadvantages of CSFQ
• Not a lot of room for allowing prioritization
• Fair amount of calculation is necessary, and may
  be futile calculation

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Queuing/Buffering Methods (cont.)

• Priority Queuing
• Multiple queues in implementation, each
  representing a level of priority (high, low, and
  a differing number in between)
• Each queue gets only packets matching its
  priority level
• Can change calculation equation on the fly

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Queuing/Buffering Methods (cont.)

• Advantages of Priority Queuing
• Simple implementation
• Very flexible
• Disadvantages of Priority Queuing
• Starvation is still possible
• If equation remains stagnant, traffic could be
  lost in the queues

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Queuing/Buffering Methods (cont.)

• Weighted Fair Queuing
• An implementation of Priority Queuing
• Classifies all traffic through a series of
  qualifications to get the traffic in the best
  possible queues
• Examples interactive traffic goes before
  non-interactive, low bandwidth sessions go before
  high bandwidth sessions

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Combing technologies

• Right now, to ensure QoS, there are no magic
  bullets
• Each technology type has many methods for a
  reason
• The way to effectively ensure QoS requirements
  best is to combine methods effectively
• As a result, we see certain technologies that we
  cannot implement fully because of the inability
  to meet the necessary QoS requirements

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Telesurgery

• Robotic and computer-aided surgery across a
  distant location
• Time-critical (delay-oriented) application
• Data to send
• surgical movements
• real-time medical images
• voice and video signal

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Telesurgery (cont.)

• QoS requirements
• reliability of the network line
• low end-to-end delay
• low data error rate
• data transfer from sources with various data
  rates
• The acceptable limit of delay requirement 330 ms

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Telesurgery (cont.)

• The use of the Internet for telesurgery is not
  possible
• ATM and SDH/SONET (optical network) meet the
  network requirements of telesurgery.

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Telesurgery (cont.)

• On September 7th, 2002, the first human
  transoceanic (New York - Strasbourg, France)
  operation was successfully performed

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Telesurgery (cont.)

• High-speed optical-fiber network
• Dedicated connection-oriented ATM transport
• Reserved bandwidth of 10 Mbps
• Measured mean-time of delays 155 ms
• ATM round trip delay 78-80 ms
• Video coding and decoding 70 ms
• Rate adaptation and Ethernet-to-ATM packet
  conversion 5 ms
• No packet loss was detected

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Remote Visualization

• Interactive viewing of 3-D scientific data sets
  over networks
• Gigabyte size range of data sets
• Interactivity ? tight delay requirement

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Remote Visualization (cont.)

• QoS requirements
• very high network bandwidth
• low latency
• constant jitter
• The use of Internet for remote visualization is
  not feasible

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Remote Visualization (cont.)

• RealityGrid implements tools for computational
  steering in the Open Grid Services Architecture
  (OGSA)

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Remote Visualization (cont.)

• High bandwidth links ? at least 700 Mbps
• Compressed video sent to remote observers ? 100 -
  200 Mbps (with low latency and constant jitter)
• These QoS requirements
• increase linearly with remote observers
• doubled again if remote stereoscopic rendering is
  employed

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Tele-Immersion

• Enable individuals in different locations to
  interact with each other in a shared,
  computer-generated environment as if they were in
  the same physical room ? Virtual Reality
• The same QoS requirements as those of remote
  visualization

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Conclusions

• Some benefits of QoS
• Control over which resources are being used
• Ensure time-critical and mission-critical
  applications have their required resources
• More efficient use of existing network resources,
  rather than the need for expansion or upgrades
• Foundation for a fully-integrated multimedia
  network needed in the near future
• QoS of scientific-computation creates technical
  challenges for designing the next generation of
  network
• The challenge of insuring QoS requirements is a
  large part of what drives todays internet