Native Simulation of Round-Robin Queuing Lachlan Richardson Glen Summers

What is Round-Robin Queuing? Each queue takes turns being served Remember previous Queue served Circular servicing Max-min fairness -> small or large packets, doesn’t matter. Each get their own service time?!?!?!

Context Used in Data Packet Scheduling Multiple incoming paths Effective utilization of network capacity ‘Share the load’ Equal priority for packets Possible scenario: New data channel built Requires another server, OR Round-Robin-Queuing Use existing server to process new data channel Split server processing equally

Simulation Setup Native discrete time simulation Fixed packet size Fixed server service rate 1 million packets per simulation Vary: Max packets in queue 0 <= Pr(pkts arrival) <= 1 Correlative probabilities between queues Measure: Dropped packets Draw discrete time diagram on the board OBJECTIVES: Simulate round-robin queuing Extrapolate results Find relationships

Intra-Queue probabilities equal, .3<P<.5 Same % arrival to both queues Vary Probability 3 approach 7 queue limit, these are before 50/50 limit Converge: towards 0 as queue limit increases

Intra-Queue probabilities equal, .45<P<.55 Around 50/50 line Stable/unstable

Intra-Queue probabilities equal, .6<P<.9 % above sum 50/50 (=1) Remainder = constant value. EG 60 – 50 = 10 (GREEN LINE) Converges to const. value

Varying queue probabilities, Sum(P) = 1 Interesting -> closely related Approach 1% pkt loss @ 18 queue limit CONVERGES

Varying queue probabilities, Sum(P) = .9 Biggest difference = least loss -> BLUE!!! 85/05 GREEN = WORST,

Conclusion Sum of probabilities should be kept less than 1 for a stable system Having a large difference in probabilities between 2 queues is not a concern Increasing queue limit decreases packet loss exponentially, however would increase the time packets spend in the system Adding a second queue to a server with round robin scheduling works well as long as the P of arrival to each queue is kept less than .5 As the P of arrivals approach .5, ensure there is adequate queue lengths Largely different probabilities between 2 queues: Stability increases!!!!