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Topics in Internet Research: Project Scope. Mehreen Alam 04030053. Contents. Objective Issues Cell Switching From Cell to Packet Switching Packet Switching Facts to Study. Objective.

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  • Objective

  • Issues

  • Cell Switching

    • From Cell to Packet Switching

  • Packet Switching

  • Facts to Study


  • Study and do throughput analysis of cell based and packet based switches, in terms of the scheduling algorithm and the switch architecture.


  • Packet vs. Cell switching

  • Delays – packet delays & average finite delays

  • throughput

  • Speed up

  • traffic pattern

    • admissible, uniform, distributions, law of large numbers, efficiency, stability

  • algorithms

    • Matching (maximal, maximum)

    • scheduling

  • simplicity and practical feasibility

  • Complexity (time, space and cost)

  • hardware implementation

  • performance evaluation

Cell switching
Cell Switching

  • Packets

    • Have variable lengths - are divided into cells of unit length

    • Switch operates on variable-size data units at their interfaces, but internally operating on cells

  • Each Packet

    • given deadline by which it must traverse the switch

  • Successful Packet

    • if the sequence of cells comprising it is contiguously transmitted out of the switch before the packet’s deadline expires

  • Retry for unsuccessful packets

    • transmission may be preempted and restarted from the beginning later.

Cell switching1
Cell Switching

  • To Study

    • Scheduling Policy - decides at each time step which packets to serve

      • use competitive analysis to measure the performance of the following scheduling policies with goals to maximize

        • the total number of successfully transmitted packets

        • the total value of successfully transmitted packets (priority)

  • pseudo-packet switching

    • Proof

      • Maximum throughput by IQ is identical to that achievable with CIOQ cell switches.

      • By simulation – IQ have performance advantages OQ

From cell to packet switching
From Cell to Packet Switching

  • Main problem in the IQ switches

    • scheduling

    • In real traffic dividing the variable packets into cells at the input side of the switch and then re-assembling these cells into packets on the output side achieve it.

  • Downside

    • bandwidth is lost as division of a packet may generate incomplete cells

    • additional overhead of segmentation and reassembling cells into packet

  • Solution

    • Send variable length packets

  • …….. Packet Switching

Packet switching
Packet Switching

  • Do packet scheduling in

    • units of arriving packet sizes, and

    • non-preemptive fashion

  • Study how packet Scheduling is

    • Stable for any admissible Bernoulli iid. arrival traffic using a simple modification of Maximum Weight Matching (MWM) algorithm, like cell-based MWM

    • Extended to general re-generative traffic model instead of just admissible traffic

    • A scenario where packet based MWM is unstable

      • But has admissible traffic pattern for any work-conserving (that is maximal type) scheduling algorithm

    • …. A new proposed waiting” MWM algorithm - stable for any admissible traffic using fluid limit technique

Facts to study
Facts to Study

  • Maximum throughput by IQ packet is identical to that achievable with CIOQ cell switches

  • For packet switches

    • IQ have performance advantages OQ

  • Stability of modified maximum weight matching for packet based switches

    • admissible traffic

    • general admissible arrival traffic

    • general re-generative traffic model

  • The Unstable scenario for packet based MWM