Topics in Internet Research: Project Scope

1. Topics in Internet Research: Project Scope Mehreen Alam 04030053

2. Contents • Objective • Issues • Cell Switching • From Cell to Packet Switching • Packet Switching • Facts to Study

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

4. Issues • 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

5. 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.

6. 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

7. 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

8. 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

9. 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

10. Q & A