• Best Effort vs. QoS
  • QoS’s Quest
  • Resource Reservation: Example
  • Cs 552 Computer Networks Quality Of Service




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    CS 552 Computer Networks Quality Of Service

    • Richard Martin
    • Credit slides by B. Nath, I. Stoica

    Outline

    • What is Quality of Service
    • Basic mechanisms
      • Leaky and token buckets
    • Integrated Services (IntServ)
    • Differentiated Services (DiffServ)
    • Economics and Social factors facing QoS
    • QoS Vs. Over Provisioning

    Best Effort vs. QoS

    • Best Effort:
        • You get a link to the Internet with at most B bits/sec.
        • If you don’t like it, switch to another provider.
    • Quality of Service (QoS)
      • We provide you some kind of guarantees for:
        • Bandwidth
        • Latency
        • Jitter
      • I.e., network is engineered to provide some Quality beyond “Not to exceed B bits/s”

    QoS’s Quest

    • The Holy Grail of computer networking is to design a network that has the flexibility and low cost of the Internet, yet offers the end-to-end quality-of-service guarantees of the telephone network.
    • --S. Keshav

    Two Styles of QoS

    • Worse-case
    • Average-case
      • Provide bandwidth/delay/jitter guarantee over many packets
      • Statistical in nature
      • E.g. “Soft real time”

    Resource Reservation: Example

    • Router
    • Router
    • Src
    • Dest
    • 4 Mbps
    • available
    • 6 Mbps
    • available
    • 10 Mbps
    • available
    • Case 1: Source attempts to connect to destination, and attempts to
    • reserve 4 Mbps for the connection
    • Result: Connection accepted. There is enough bandwidth
    • available. Available link bandwidths updated.
    • Case 2: Source attempts to connect to destination, and attempts to
    • reserve 5 Mbps for the connection
    • Result: Failure. There is not enough bandwidth available on
    • one of the links.

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