Topics in Internet Research: Project Scope Mehreen Alam

Contents  Objective  Issues  Cell Switching From Cell to Packet Switching  Packet Switching  Facts to Study

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

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

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 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  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  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  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

Q & A