QoS in Networks CS680

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QoS in NetworksCS680

• Prof. A. Sahoo

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Topics to be Covered

• Introduction
• Integrated Services
• Architecture
• Service models
• Guaranteed service
• Controlled load service
• RSVP
• Salient parts of RFC 2205
• Packet scheduling (various scheduling mechanisms
  e.g. max-min fair scheduling, GPS, WFQ, WRR etc.)

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Topics to be Covered

• Differentiated Services
• Basic approach
• PHBs
• Services
• Diffserv fields
• Traffic classification and conditioning
• AF PHB
• EF PHB
• Traffic Policing
• IntServ over DiffServ
• Congestion control

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Topics to be Covered

• Multiprotocol Label Switching
• Motivation
• Label switching proposals (tag switching, IP
  switching etc.)
• MPLS architecture
• Salient parts of RFC 3031
• Label Distribution Protocols

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Topics to be Covered

• Traffic description methods and Delay Analysis
• Internet Traffic Engineering
• The Fish Problem
• Building blocks of TE
• Constraint based routing
• Multipath load sharing
• QoS based routing
• QoS in Wireless Network
• Virtual Private Network
• Papers in those topics

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Books and References

• Internet QoS Architecture and Mechanisms for
  Quality of Service -
• Zheng Wang, Publisher Morgan Kauffman.
• MPLS Technology and Application B. Davie, Y.
  Rekhter, Publisher Morgan Kauffman.
• An Engineering Approach to Computer Networking-
  S. Keshav, publisher Addison-Wesley.
• Various RFCs and papers.

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Prerequisite

• UG or PG course in Computer Networks
• Understanding of MAC, routing, TCP/IP protocols
• Basics in Algorithms
• Basics in Queueing Theory

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Class Evaluation

• Surprise Quizzes 10
• Mid sem 30
• End sem 40
• Course Project 20

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Grading Policy

• Based on clustering

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Pre-Requisite

• Undergraduate Computer Networks Knowledge
• Understanding of TCP, IP routing protocols,
  various MAC protocols
• Basic knowledge in probability theory
• Basic understanding of queuing theory

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Other Academic Policies

• Academic dishonesty
• Will not be tolerated at all
• Will get fail grade for doing so
• Attendance Policy
• As per Institute rule
• Falling Short will get you XX grade

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Introduction (contd)

• For Many Years Internet was primarily used for
  networking research. File transfer, email were
  the most popular application They do not need
  any performance guarantee from underlying
  network.
• New applications such as VoIP, video
  conferencing, e-commerce apps are sensitive to
  network performance.

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Introduction (contd)

• Internet cannot provide any resource guarantees
  the service is best effort
• Internet does not provide service differentiation
  all packets are treated equal.
• But applications such as VoIP require low delay,
  jitter and packet loss whereas file transfer app
  can tolerate fair amount of delay and loss. Thus
  there is a need to differentiate between packets
  of such applications.

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Current State of Internet

• Uses best-effort service model
• No guarantee of timeliness of delivery
• No service discrimination
• Bandwidth and network congestion problems
• Unpredictable network response time

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What is QoS

• The capability to provide resource assurance and
  service differentiation so that delay, jitter or
  loss sensitive applications can perform
  satisfactorily is often referred to as quality of
  service (QoS).
• can be provided through relative prioritization
  of resource allocation to different flows/packets
  in the network.

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QoS

• QoS parameters
• At bit level
• Bit error rate
• At Packet level
• Delay
• Delay Jitter
• Packet loss
• Throughput
• At call level
• Blocking probability
• At Application level
• Throughput
• Response time

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QoS

• QoS in circuit-switched network
• Quite Easy
• QoS in packet-switched network
• Difficult (why?)
• Wired network
• Wireless network
• Inherent limitation of protocols
• Queuing

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Resource Allocation

• Many problems in the Internet come down to issue
  of resource allocation.
• Packets get delayed or dropped because network
  resource cannot meet the traffic demands.
• A network consists of shared resources
  bandwidth, buffer, serving traffic from competing
  users.
• To support QoS network must allocate resources
  and decide who should get how much resources.

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Resource Allocation (contd)

• Current Internet does not support active resource
  allocation.
• Network treats all packets equally and then
  serves FCFS.
• Hence current Internet offers best effort
  service.
• Adequate for some apps (e.g. file transfer), but
  not suitable for realtime apps.

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Integrated Services

• Based on per flow resource reservation.
• Apps must make a reservation before transmitting
  traffic.
• App characterize its traffic and resource
  requirement.
• Network uses routing protocol to find a path.
• A reservation protocol is used to install the
  reservation state along that path.

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Integrated Services (contd)

• At each hop, admission control checks whether
  sufficient resources are available to accept the
  new reservation.
• Resource reservation enforced by packet
  classification and scheduling mechanisms.
• Two new service models were introduced
  guaranteed service and controlled load.
• Guaranteed service provides deterministic worst
  case delay
• Controlled load provides less firm guarantee
  its close to a lightly loaded best-effort
  network.

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Integrated Services (contd)

• Overhead of setting up reservation is high.
• Scalability problem Backbone will have a large
  number of flows and keeping flow information is
  not feasible.

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Differentiated Service

• User traffic is divided into a small number of
  forwarding classes.
• For each forwarding class, the amount of traffic
  that users can inject is limited at the edge of
  the network.
• Edge of a differentiated Services network
  responsible for mapping packets to their
  appropriate forwarding classes.
• Packet classification is usually based on service
  level agreement.

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Differentiated Service (Contd)

• Nodes at the edge of the network perform traffic
  policing to ensure conformance.
• Non-conforming traffic may be dropped, delayed or
  marked with a different forwarding class.
• Forwarding class is directly encoded into the
  packet header.
• Interior nodes use this info. to differentiate
  the treatment of packets.
• Does not require resource reservation.

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Differentiated Service (Contd)

• Forwarding classes apply to traffic aggregates
  rather than individual flows.
• No scalability problem.

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Multiprotocol Label Switching (MPLS)

• A short fixed length label is encoded into the
  packet header and is used for packet forwarding.
• When a label switch router (LSR) receives a MPLS
  packet, it uses incoming label to find the next
  hop and the corresponding outgoing label.
• In MPLS, the path a packet traverses is called
  label switched path (LSP).
• Network protocol independent

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Multiprotocol Label Switching (MPLS)

• Works alongside existing routing technologies and
  provide a mechanism for explicit control over
  routing paths.
• Used for traffic engineering, guaranteeing QoS
  and VPN.

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Traffic Engineering

• The basic problem Given a network and traffic
  demands, how can traffic flows in the network be
  organized so that an optimization objective can
  be achieved.
• Typically optimal operating point is reached when
  traffic is evenly distributed leads to min
  queuing delay and packet loss.
• This cannot be achieved through destination based
  IP routing
• Advanced routing techniques constraint-based
  routing are used.

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Traffic Engineering (contd)

• Routes are computed with multiple constraints and
  aims for efficient resource utilization.
• Appropriate path selection with uniform traffic
  distribution and the congestion avoidance
  techniques improve the network performance
• MPLS can be used to achieve this goal.

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QoS based Routing

• Basic routing protocols do not consider any QoS
  parameters e.g. delay, packet loss.
• They are dynamic in terms of topology changes due
  to link or node failure
• But static in terms of performance of the network
  w.r.t. delay, packet loss etc
• QoS based routing provides a mechanism to get QoS
  support from the routing protocol.

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QoS based Routing (contd)

• Study few mechanisms proposed in literature
• Shortest Path First with Emergency Exits
• OSPF Extension with QoS routing (RFC 2676)
• OSPF based Load Sensitive Routing

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QoS in Wireless Network

• Mostly study IEEE 802.11 based network
• 802.11 MAC is a contention based (CSMA/CA) MAC
• Hence there is no guarantee/assurance for an
  application to have bounded delay/packet loss
• Look at various proposals in literature that
  addresses the QoS issues

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QoS in Wireless Network (contd)

• DCF
• Some enhancement to DCF for QoS
• EDCA
• Distributed Fair Scheduling in MAC
• Wireless Token Ring Protocol
• Blackburst