Quality of Service Traffic Engineering (QoS TE) Khaled Mohamed

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					                                                                CSIS




             Quality of Service &
             Traffic Engineering
                (QoS & TE)
                            Khaled Mohamed

             Credit: some of the sides are from Cisco Systems


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                             Agenda

    •        QOS and TE in IP Network
    •        The QoS and TE Architectures
    •        QOS and TE Service Types
    •        The Technical Scenarios Reasons
    •        The Applications and Their Needs
    •        Q&A


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                   QoS in IP Networks
     Thus far: ―making the best of best effort‖
     Future: next-generation Internet with QoS guarantees
        – Differentiated Services: differential guarantees
        – Integrated Services: firm guarantees
     • Example: guarantees an audio application 1Mbps; the
       remaining to 0.5Mbps to Web transfer




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             Principles for QoS Guarantees




             packet classification: router can distinguish
             between different classes



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                Principles for QoS Guarantees
      • prevents applications from misbehaving (e.g.,
        multimedia app. sends higher than declared
        rate)




             scheduling and policing: provide protection (isolation)

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                Principles for QoS Guarantees
    • Allocating fixed (non-sharable) bandwidth to
      flow: inefficient use of bandwidth if flows
      doesn’t use its allocation




             high utilization: while providing isolation, it is
             desirable to use resources as efficiently as possible

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                Principles for QoS Guarantees
      • Basic fact of life: cannot support traffic
        demands beyond link capacity




             call admission: flow declares its needs, network may
             block call (e.g., busy signal) if it cannot meet needs

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             Summary of QoS Principles




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                       Traffic Specification
    Three common-used criteria:
    • (Long term) Average Rate: how many pkts can be
      sent per unit time (in the long run)
             – crucial question: what is the interval length: 100 packets
               per sec or 6000 packets per min have same average!
    • Peak Rate: e.g., 6000 pkts per min. (ppm) avg.; 1500
      ppm peak rate
    • (Max.) Burst Size: max. number of pkts sent
      consecutively (with no intervening idle)


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                     Traffic Specification
      Token Bucket: limit input to specified Burst Size
             and Average Rate.




      • bucket can hold b tokens
      • tokens generated at rate r token/sec unless bucket full
      • over interval of length t: number of packets admitted less
        than or equal to (r t + b).
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                   Scheduling Mechanisms
      • scheduling: choose next packet to send on link
      • FIFO (first in first out) scheduling: send in order of
        arrival to queue
             – discard policy: if packet arrives to full queue: who to discard?
                • tail drop: drop arriving packet
                • priority: drop/remove on priority basis
                • random: drop/remove randomly




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                 Scheduling Policies: more
      Priority scheduling: transmit highest priority
        queued packet
      • multiple classes, with different priorities
             – class may depend on marking or other header
               info, e.g. IP source/dest, port numbers, etc..




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             Scheduling Policies: still more
     round robin scheduling:
     • multiple classes
     • cyclically scan class queues, serving one
       from each class (if available)




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             Scheduling Policies: still more
      Weighted Fair Queuing:
      • generalized Round Robin
      • each class gets weighted amount of service
        in each cycle




        .
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                       Delay Guarantees
     • token bucket, WFQ combine to guarantee
       upper bound on delay, i.e., QoS guarantee!

        arriving   token rate, r
        traffic

                   bucket size, b
                                    assigned
                                    flow rate, R
                            WFQ

                         D = b/R
                          max


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               QOS Type of Services

      Integrated services
      • Differentiated services




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                    IETF IntServ Services
      • Architecture for providing QoS guarantees in IP
        networks for individual application sessions


      • Assumptions
             – use a common infrastructure for both real-time
               and non-real-time communications
             – resource must be explicitly managed in order to
               meet the requirements of real-time applications
                • resource reservation: routers maintain state info (a la VC) of
                  allocated resources, QoS req’s


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             Intserv QoS: Service Models [rfc2211, rfc 2212]
     Guaranteed service:                       Controlled load service:
     • worst case traffic arrival:             • "a quality of service closely
       leaky-bucket-policed source               approximating the QoS that
     • simple (mathematically                    same flow would receive
       provable) bound on delay                  from an unloaded network
       [Parekh 1992, Cruz 1988]                  element."
       arriving     token rate, r
       traffic                                 Controlled link sharing:
                                              • Sharing link among
                    bucket size, b
                                     per-flow
                                                different classes
                                     rate, R
                             WFQ

                          D = b/R
                           max
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                Reference Architecture
Routing                                                                            RSVP
                            Routing           RSVP
Messages                                                                          messages




                                                                  Control Plane
                                                     Admission
                                                      Control




                                                                     Data Plane
                Forwarding Table           Per Flow QoS Table

      Data In
                Route Lookup          Classifier      Scheduler                   Data Out


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             A Closer Look at the Data Path
                          Per-flow State
                               …

                                flow 1

                                flow 2
                 Classifier                Scheduler
                                flow n


                              Buffer
                              management




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             Intserv: QoS Guarantee Scenario
                              • Resource reservation
                                 – call setup, signaling (RSVP)
                                 – traffic, QoS declaration
                                 – per-element admission control



                                          request/
                                            reply

             – QoS-sensitive scheduling
               (e.g., WFQ)

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                  RSVP Protocol
     A flow needs performance guarantee must :
     • declare its QoS requirement
        – R-spec: defines the QoS being requested
     • characterize traffic it will send into network
        – T-spec: defines traffic characteristics
     • signaling protocol: needed to carry R-spec and
       T-spec to routers (where reservation is
       required)
        – RSVP
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                       RSVP: Soft-state Receiver-initiated
                           End-to-End Reservation
     • Sender periodically sends PATH messages to receiver R, each router
       updates the PATH message by increasing hop count and adding its
       propagation delay
     • When receiver R gets the PATH message, it knows
             – Traffic characteristics (tspec): (r,b,R)
             – Number of hops, propagation delay introduced by the routers
     • Receiver R sends back this information + required worst-case delay in
       RESV
     • Each router along path provides a per-hop delay guarantee and forwards
       RESV with updated info
             – In the simplest case, the routers can just split the delay
             – State timed out if not refreshed
                                                R2                             R
                 S
                            R1                                     R3
   RESV
   PATH
                                                                             delay budget

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                    Implementing IntServ
     • Use WFQ to
                                             WFQ
       implement controlled
                                                   CS department
       link sharing among                             gets 50%

       different
                                                   WFQ
       organizations
     • WFQ provides                                 10%
                                                            30%

       guaranteed service
                                guaranteed    guaranteed    priority
     • Controlled-load and        flow 1        flow n

       best-effort flows are
                                                    controlled     best effort
       separated by priority                          flows           flows



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                IETF Differentiated Services
     Concerns with Intserv:
     • Scalability: signaling, maintaining per-flow router state
             difficult with large number of flows
     • Flexible Service Models: Intserv has only two classes.
             Also want ―qualitative‖ service classes
              – ―behaves like a wire‖
              – relative service distinction: Platinum, Gold, Silver
     Diffserv approach:
     • simple functions in network core, relatively complex
       functions at edge routers (or hosts)
     • Don’t define service classes, provide functional
       components to build service classes
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        The DiffServ Traffic Conditioner Block (TCB)




   •     Classifier: Identifies packets for assignment to Classes
   •     Meter: Checks compliance to traffic parameters (Token Bucket) and passes result to
         Marker and Shaper/Dropper to trigger particular action for in/out-of-profile packets
   •     Marker: Writes/rewrites the DSCP value
   •     Shaper: Delays some packets for them to be compliant with the profile
   •     Dropper: Drops packets that exceed the profile (Bc or Be)


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                                                 marking
                                             r
    DiffServ Architecture                           scheduling
    Edge router:                         b
    - per-flow traffic management
                                                       .
                                                       .
                                                       .
    - marks packets as in-profile
    and out-profile


      Core router:
      - per class traffic management
      - buffering and scheduling
      based on marking at edge
      - preference given to in-profile
      packets
      - Assured Forwarding

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             Edge-router Packet Marking
  • profile: pre-negotiated rate A, bucket size B
  • packet marking at edge based on per-flow profile
                                    Rate A

                                       B


                     User packets

   Possible usage of marking:
     • class-based marking: packets of different classes marked
       differently
     • intra-class marking: conforming portion of flow marked
       differently than non-conforming one

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             Classification and Conditioning
    • Packet is marked in the Type of Service (TOS)
      in IPv4, and Traffic Class in IPv6
    • 6 bits used for Differentiated Service Code
      Point (DSCP) and determine PHB that the
      packet will receive
    • 2 bits are currently unused




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             Classification and Conditioning
    may be desirable to limit traffic injection rate of
    some class:
  • user declares traffic profile (eg, rate, burst size)
  • traffic metered, shaped if non-conforming




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                Forwarding (PHB)
    • PHB result in a different observable (measurable)
      forwarding performance behavior
    • PHB does not specify what mechanisms to use to
      ensure required PHB performance behavior
    • Examples:
       – Class A gets x% of outgoing link bandwidth over
         time intervals of a specified length
       – Class A packets leave first before packets from
         class B

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                      Forwarding (PHB)
    PHBs being developed:
    • Expedited Forwarding: pkt departure rate of a
      class equals or exceeds specified rate
             – logical link with a minimum guaranteed rate
    • Assured Forwarding: 4 classes of traffic
             – each guaranteed minimum amount of bandwidth
             – each with three drop preference partitions



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                           Why QoS?
             Congestion Scenario #1—Speed Mismatch
                 100Mbps             2Mbps
                                                    WAN



                1000Mbps             100Mbps




                           Direction of Data-Flow

  • The #1 Reason for Congestion!
  • Possibly Persistent when going from LAN to WAN
  • Usually Transient when going from LAN to LAN!
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                             Why QoS?
                 Congestion Scenario #2—Aggregation
    HQ                      Hubi
                   2Mbps                 512Kbps
                                                    FR/ATM


                                                        N*56Kbps
Choke
Points                                                             Remote
                                    S1                      S2
                     1000Mbps
                                          1000Mbps



                                                      Choke
                                                      Point

                                   Direction of Data-Flow
    •        Transient Congestion fairly typical!
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                                 Why QoS??
                     Congestion Scenario #3—Confluence
             Net-1

                              Core1                    Core2


        Net-2                         STM-64/OC-192c

      STM-16/OC-48c


                      Net-n



   • Always need mechanisms to provide guarantees!
   • Transient Congestion occurs!
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                           Typical Application
                                QoS Requirements
                                   Voice       FTP         ERP and
                                                        Mission-Critical
                                   Low to    Moderate
              Bandwidth                                      Low
                                  Moderate    to High

                                                           Moderate
  Random Drop Sensitive             Low       High
                                                           To High
                                                            Low to
             Delay Sensitive        High       Low
                                                           Moderate

             Jitter Sensitive       High       Low         Moderate




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               Q&A
             Thank You

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