TN3435 Multimedia Communications Lecture 10

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TN3435 Multimedia CommunicationsLecture 10
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Overview

• Multimedia traffic descriptors
• Congestion concepts
• Introduction to QoS
• QoS in Packet Switched Network
• Techniques to improve QoS
• Scheduling,Traffic shaping, Resource reservation,
  Admission control
• QoS Mechanism for the Internet
• Integrated Services(IntServ), RSVP.
• Differentiae Service (diffserv)
• Implementing QoS

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Multimedia Traffic Descriptor - 1

• Characterized by throughput variation with time
• constant bit rate
• variable bit rate - conserve transmission
  capacity or to control display quality
• Bursty

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Multimedia Traffic Descriptor - 2
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Multimedia Traffic Descriptor - 3
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Multimedia Traffic Descriptor - 4

• The average data rate indicates the average
  bandwidth needed by the traffic.
• The peak data rate defines the maximum data rate
  of the traffic.
• The maximum burst size refers to the maximum
  length of time the traffic is generated at the
  peak rate.
• The effective bandwidth is a function of three
  values average data rate, peak data rate, and
  maximum burst size.

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CONGESTION - 1

• Congestion in a network occurs if the load on the
  network - the number of packets sent to the
  network is greater than the capacity of the
  network.
• Congestion in a network occurs because routers
  and switches have queues/buffers that hold the
  packets before and after processing.
• Congestion can be long-lived or transient.

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CONGESTION - 2
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CONGESTION - 3

• Routers maintain packet queues (or buffers).
• Buffers fill up if
• Routers are too slow, OR
• Combined input traffic rate exceeds the outgoing
  traffic rate
• Insufficient buffer space leads to congestion.

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Introduction to QoS

• The operational parameters associated with a
  communications channel through a network are
  known as the network Quality of Service (QoS)
  parameters.
• These parameters collectively determine the
  suitability of the channel.
• We will focus on the QoS parameters associated
  with a packet-switched network.

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QoS parameters associated with a packet-switched
network

• Maximum packet size
• Mean packet transfer rate
• Mean packet error rate (PER)
• Mean packet transfer delay
• Worst-case jitter
• Transmission delay

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Quality of Service What is it?
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Network QoS Parameters - 1

• Internet Jitter and Delay

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Network QoS Parameters - 2

• Three typical QoS parameters
• Delay transmission speed
• Throughput transmission capacity
• Loss error probability, error treatment

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Network QoS Parameters - 3

• Mean packet transfer delay
• packet size
• maximum link bit rates
• store-and-forward delays in switches/router

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Application QoS - 1

• Application QoS defines the QoS parameters
  required by a given application.
• They relate in part to network QoS parameters
• Frame/Sample size
• Frame rate or required bit/packet rate
• Maximum end-to-end delay
• Maximum delay variation/jitter
• Loss rate (frames, Application Data Units)
• Maximum start-up delay

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Application QoS - 2
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User QoS

• User QoS specify the QoS how it is accepted by
  the user. These parameters cannot always
  quantified.
• Delay of connection set up
• Quality of presentation (colour, synchronization,
  sound quality)
• Security

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TECHNIQUES TO IMPROVE QOS - 1

• Scheduling
• Traffic shaping
• Admission control
• Resource reservation

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TECHNIQUES TO IMPROVE QOS - 2

• Scheduling
• Packets from different flows arrive at a switch
  or router for processing.
• Scheduling techniques determine how to output the
  different flows.
• FIFO queuing
• Priority queuing
• Weighted fair queuing.

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TECHNIQUES TO IMPROVE QOS - 3

• FIFO Queuing
• In first-in, first-out (FIFO) queuing, packets
  wait in a buffer (queue) until the node (router
  or switch) is ready to process them.
• If the average arrival rate is higher than the
  average processing rate, the queue will fill up
  and new packets will be discarded.

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TECHNIQUES TO IMPROVE QOS - 4

• Priority Queuing
• In priority queuing, packets are first assigned
  to a priority class.
• Each priority class has its own queue.
• The packets in the highest-priority queue are
  processed first.
• Packets in the lowest-priority queue are
  processed last.
• The system does not stop serving a queue until it
  is empty.

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TECHNIQUES TO IMPROVE QOS - 5
Potential drawback starvation If there is a
continuous flow in a high-priority queue, the
packets in the lower-priority queues will never
have a chance to be processed.
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TECHNIQUES TO IMPROVE QOS - 6

• Weighted Fair Queuing
• The queues are weighted based on the priority of
  the queues.
• Higher priority means a higher weight.
• The system processes packets in each queue in a
  round-robin fashion with the number of packets
  selected from each queue based on the
  corresponding weight.
• This guaranteed that the lower priority queues
  will be served.

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TECHNIQUES TO IMPROVE QOS - 7
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TECHNIQUES TO IMPROVE QOS - 8

• Traffic Shaping
• A mechanism to control the amount and the rate of
  the traffic sent to the network.
• Two techniques can shape traffic
• Leaky bucket
• Token bucket

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TECHNIQUES TO IMPROVE QOS - 9

• Leaky Bucket - 1
• Variable input rate, but the output rate remains
  constant.
• A leaky bucket algorithm shapes bursty traffic
  into fixed-rate traffic by averaging the data
  rate.
• Without the leaky bucket, these bursty data may
  have hurt the network by consuming more bandwidth
  than it is allowed.
• It may drop the packets if the bucket is full.

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TECHNIQUES TO IMPROVE QOS - 10

• Leaky Bucket - 2

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TECHNIQUES TO IMPROVE QOS - 11

• Leaky bucket implementation - 1

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TECHNIQUES TO IMPROVE QOS - 12
Purpose To control the output data rate to be
always less than a fixed rate where the size of
each packet can be different.
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TECHNIQUES TO IMPROVE QOS - 13
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TECHNIQUES TO IMPROVE QOS - 14

• Leaky bucket calculation - 1
• Queue Size required for a burst (S, Mb)
• Peak Bursty Input rate (I, Mbps)
• Data duration (t, sec)
• Fixed Output rate (O, Mbps)
• S (I O) x (t)
• If I gtgt O
• S (I) x (t)

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TECHNIQUES TO IMPROVE QOS - 15

• Leaky bucket calculation - 2
• Find Queue Size required for a burst (S, Mb)
• Given
• Peak Bursty Input rate (I, Mbps) 40 Mbps
• Data duration (t, sec) 0.1 sec
• Fixed Output rate (O, Mbps) 1.544 Mbps
• S (I O)(t)
• (40 1.544) (0.1)
• If I gtgt O
• S (40) (0.1) Answer 4 Megabits

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TECHNIQUES TO IMPROVE QOS - 16

• Token Bucket - 1
• In the leaky bucket algorithm, the time when the
  host was idle is not taken into account.
• The token bucket algorithm allows idle hosts to
  accumulate credit for the future in the form of
  tokens.
• For each tick of the clock the system sends n
  tokens to the bucket.
• The host can send bursty data as long as there
  are tokens still in the bucket.

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TECHNIQUES TO IMPROVE QOS - 17

• Token Bucket - 2
• For example, if n is 100 and the host is idle for
  100 ticks, the bucket collects 10,000 tokens.
• Now the host can consume all these tokens in one
  tick with 10,000 bytes, or the host takes 1000
  ticks with 10 bytes per tick.
• The token bucket allows bursty traffic at a
  regulated maximum rate.

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TECHNIQUES TO IMPROVE QOS - 18

• Token Bucket 3

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TECHNIQUES TO IMPROVE QOS - 19

• Resource Reservation
• A flow of data needs resources such as a buffer,
  bandwidth, CPU time, and so on.
• The quality of service is improved if these
  resources are reserved beforehand.

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TECHNIQUES TO IMPROVE QOS - 20

• Admission Control
• Admission control refers to the mechanism used by
  a router, or a switch, to accept or reject a flow
  based on predefined parameters called flow
  specifications.
• Before a router accepts a flow for processing, it
  checks the flow specifications to see if its
  capacity (in terms of bandwidth, buffer size, CPU
  speed, etc.) and its previous commitments to
  other flows can handle the new flow.

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TECHNIQUES TO IMPROVE QOS - 21

• The gatekeeper on the right enforces Call
  Admission Control

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QoS in the Internet - 1

• The Internet is rapidly becoming a commercial
  infrastructure.
• Increasing user expectation for better service.
• Differential treatment to different traffic.
• Application level requirements for QoS.

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QoS in the Internet - 2

• The Current Internet
• Based on the TCP/IP protocols suite.
• IP provides only best effort service.
• IP designed to run over everything.
• IP has minimal expectations from the underlying
  network access layer.
• The emphasis is on providing connectivity.
• IP does not participate in resource management,
  thus cannot provide QoS.

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QoS in the Internet - 3

• Internet use packet switched technology where
  resources are statistically shared.
• Resources
• Link Bandwidth
• Buffer space at routers and switches
• QoS can be provided through resource management.

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QoS in the Internet - 4

• Two tasks to be done to achieve QoS
• Pre-allocate resources to avoid congestion
• Control congestion if it (and when) is occurred
• Two points of implementation
• At edges of the network
• At routers inside the network

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QoS The IntServ Approach - 1

• Integrated Services (IntServ), is a flow-based
  QoS model.
• A user needs to create a flow, a kind of virtual
  circuit from the source to the destination and
  inform all routers of the resource requirement.
• Need Resource Reservation Protocol (RSVP) - a
  signaling protocol to run over IP that provides
  the signaling mechanism for making a reservation.

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QoS The IntServ Approach - 2

• Flow Specification
• When a source makes a reservation, it needs to
  define a 2-parts flow specification.
• Rspec (resource specification) - defines the
  resource that the flow needs to reserve (buffer,
  bandwidth. etc.)
• Tspec (traffic specification) - defines the
  traffic characterization of the flow.

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QoS The IntServ Approach - 3

• Two classes of services have been defined for
  Integrated Services.
• 1. Guaranteed Service Class
• For real-time traffic that needs a guaranteed
  minimum end-to-end delay.
• This delay is the sum of the delays in the
  routers, the propagation delay in the media, and
  the setup mechanism.
• Only the sum of delays in the routers, can be
  guaranteed by the router.

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QoS The IntServ Approach - 4

• The Guaranteed Service Class guarantees that the
  packets will arrive within a certain delivery
  time and are not discarded if flow traffic stays
  within the boundary of Tspec.
• 2. Controlled-Load Service Class
• For applications that can accept some delays, but
  are sensitive to an overloaded network and to the
  danger of losing packets.
• Examples of these types of applications are file
  transfer, email, and Internet access.

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QoS The IntServ Approach - 5

• How RSVP works 1
• In RSVP, the receivers make the reservation.
• First, a Path message travels from the sender and
  reaches all receivers in the multi-cast path.
• On its way, a Path message stores the necessary
  information for the receivers.

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QoS The IntServ Approach - 6

• How RSVP works 2
• After a receiver has received a Path message, it
  sends a Resv message.
• The Resv message travels toward the sender
  (upstream) and makes a resource reservation on
  the routers that support RSVP.
• If a router does not support RSVP on the path, it
  routes the packet based on best-effort delivery.

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QoS The IntServ Approach - 7

• How RSVP works 3
• Reservation Merging In RSVP, the resources are
  not reserved for each receiver in a flow the
  reservation is merged.

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Integrated Services (IntServ) Model Analogy

• A fire engine would radio ahead to the nearest
  intersection before it left the fire station.
• Police stationed at each intersection would
  contact each other to announce the fire engine
  was coming, and to access the traffic conditions.
• A special lane might be reserved by the police so
  that the fire engine could move at full speed all
  the way toward the destination regardless of
  what other traffic might be present.
• Advanced reservation is required on a per-flow
  basis.

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Summary QoS - The IntServ

• Limitations with Integrated Services
• Scalability
• The Integrated Services model requires that each
  router keep information for each flow.
• As the Internet is growing every day, this is a
  serious problem.
• Service-Type Limitation
• Integrated Services provides only two types of
  services, guaranteed and control-load.
• This may not be adequate for some Internet
  applications.

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QoS The DiffServ Approach - 1

• Intended to address the following difficulties
  with IntServ and RSVP
• Scalability maintaining states by routers in
  high speed networks is difficult due to the very
  large number of flows
• Flexible Service Models IntServ has only two
  classes, want to provide more qualitative service
  classes (Platinum, Gold, Silver, )
• Simpler signaling than RSVP.

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QoS The DiffServ Approach - 2

• Two fundamental changes were made for DiffServ.
• The main processing was moved from the core of
  the network to the edge of the network.
• This solves the scalability problem.
• The routers do not have to store information
  about flows.
• The applications define the type of service they
  need each time they send a packet.
• The per-flow service is changed to per-class
  service.
• The router routes the packet based on the class
  of service defined in the packet.
• This solves the service-type limitation problem.
• Different types of classes based on the needs of
  applications can be defined.

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QoS The DiffServ Approach - 3

• Edge routers traffic conditioning (policing,
  marking, dropping), service level agreement (SLA)
  negotiation
• Set values in DS-byte in IP header based upon
  negotiated service and observed traffic.
• Interior routers traffic classification and
  forwarding.
• Use DS-byte as index into forwarding table.

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QoS The DiffServ Approach - 4

• Packet format support
• Packet is marked in the Type of Service (TOS) in
  IPv4, and Traffic Class in IPv6 renamed as DS.
• 6 bits used for Differentiated Service Code Point
  (DSCP) and determine per-hop behavior (PHB) that
  the packet will receive
• 2 bits are currently unused.

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QoS The DiffServ Approach - 5

• Three Per-Hop Behavior (PHB) are defined.
• DE PHB
• The DE PHB (default PHB) is the same as
  best-effort delivery, which is compatible with
  TOS.
• EF PHB
• The EF PHB (expedited forwarding PHB) provides
  the following services
• Low loss
• Low latency
• Ensured bandwidth
• This is the same as having a virtual connection
  between the source and destination.

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Classification Tools
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Mapping of IP Precedence and DSCP Fields (1)
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Mapping of IP Precedence and DSCP Fields (2)
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QoS The DiffServ Approach - 6

• AF PHB
• The AF PHB (assured forwarding PHB) delivers the
  packet with a high assurance as long as the class
  traffic does not exceed the traffic profile of
  the node.
• The users of the network need to be aware that
  some packets may be discarded.

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Classification Recommendations

• Voice Bear Traffic
• Recommendation DSCP EF, IP Precedence 5, COS 5
• Video Conferencing
• Recommendation DSCP AF41, IP Precedence 4, COS
  4
• Streaming Video
• Recommendation DSCP AF13, IP Precedence 1, COS
  1
• Mission-Critical Data
• Recommendation Gold Class or mission-criticalDS
  CP AF21-23, IP Precedence 2, COS 2
• Silver ClassDSCP AF11-13, IP Precedence 1, COS
  1
• Best-Effort Data
• Recommendation DSCP BE, IP Precedence 0, COS 0

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QoS The DiffServ Approach - 7

• Traffic Conditioner
• To implement DiffServ, the DS node uses the
  following traffic conditioners meters, markers,
  shapers, and droppers.

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QoS The DiffServ Approach - 8

• Meter
• The meter checks to see if the incoming flow
  matches the negotiated traffic profile.
• The meter also sends this result to other
  components.
• Marker
• A marker can down-mark (lowering the class of the
  flow) a packet based on information received from
  the meter. This can occur if the flow does not
  match the profile.
• A marker does not up-mark (promote the class) a
  packet.

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QoS The DiffServ Approach - 9

• Shaper
• A shaper uses the information received from the
  meter to reshape the traffic if it is not
  compliant with the negotiated profile.
• Dropper
• A dropper, which works like a shaper with no
  buffer, discards packets if the flow severely
  violates the negotiated profile.

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Differentiated Services (DiffServ) Model Analogy

• Continuing with the fire engine analogy, here
  polices are stationed at every intersection as
  before. However, none of them know a fine engine
  is coming until they see the lights or hear the
  siren.
• A each intersection, a decision is made as to how
  to handle the approaching fire engine. Other
  traffic can be held back, if needed, so that the
  fire engine can go right through.
• QoS is handled dynamically, in a distributed
  fashion on a per-hop or per-class basis.

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Implementing QoS - 1
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Implementing QoS - 2

• QoS is best applied to an already solid network
  design, i.e. a network with
• High availability
• Redundancy techniques and failover designed in
  and tested
• Fast convergence

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Implementing QoS - 3

• Four steps as shown on the right.
• The first phrase is to initial lab or field
  testing of QoS and QoS tools.
• The testing phrase also aims to build up staff
  understanding and skills on QoS.

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Implementing QoS - 4

• There are four steps involved in building a
  QoS-Capable Network
• 1. Baseline network
• To have a survey of the devices on current
  network, the firmware software versions, and the
  IP addressing scheme etc.
• 2. Capacity planning
• Collect current network devices utilization and
• Collect current application mix
• Projected new applications, especially network
  backup and high bandwidth application

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Implementing QoS - 5

• 3. Network re-design
• Deploy QoS-capable devices as needed
• Resolve bandwidth (capacity) problems, usually in
  the WAN
• Build hierarchical redundant WAN and campus
  networks
• Design, implement, and test use of appropriate
  protocols to achieve quick failover
• 4. Baseline new network
• Make sure it works as needed
• Avoid finding problems later

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Implementing QoS - 6

• Determine QoS policy
• This can be done concurrent with the previous
  task
• Need to consider the current and projected
  application mix and traffic volumes and come up
  with a QoS policy
• Focus on the more critical issues first, can
  later re-visit for fine-tuning
• Priority for VoIP or IP Video Conferencing
• Protect from excess video, audio, file transfer,
  backup, or other large flows
• Provide protected bandwidth for critical data
  applications
• Deploying QoS
• Usually QoS is more critical in the WAN

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Implementing QoS - 7

• Some Management Practices
• Procedures to ensure operations staff does no
  harm
• Performance reporting
• Visibility into what the worst problem areas are
• Measure incremental improvement
• Understand what deployed QoS policy is doing
• Understand applications and flows on each
  interface