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Auteur(s) Bonaventure Olivier
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Se connecter

Se connecter

Round-robin scheduling

The round-robin scheduler servers packets in the different queues according to a fixed cyclic schedule. For this exercise, we assume that the schedule is Q1, Q2, Q3, Q1, Q2, Q3, ...

The scheduler is attached to a 1 Mbps link. All incoming flows also arrive on 1 Mbps links.

The packets that arrive in queue Q1 are represented using upper case letters. The packets that arrived in Q2 are represented using lower case letters and the packets in Q3 use digits. A dot (.) in the incoming traffic pattern corresponds to a period of one millisecond without any incoming packet. For this exercise, we assume that all packets are 1000 bits long.

Question 1: Incoming traffic pattern

Queue Q1 receives the following packets (A is the first received packet) :

  • JIHGFEDCBA

Queue Q2 receives the following packets (a is the first received packet) :

  • jihgfedcba

Queue Q3 receives the following packets (0 is the first received packets) :

  • 9876543210

Assuming the Q1-Q2-Q3 schedule, what are the first ten packets sent on the output link ?

Question 2: incoming traffic pattern

Queue Q1 receives the following packets (A is the first received packet) :

  • JIHGFEDCBA

Queue Q2 receives the following packets (a is the first received packet) :

  • edcba.....

Queue Q3 receives the following packets (0 is the first received packets) :

  • .....43210

Assuming the Q1-Q2-Q3 schedule, what are the first ten packets sent on the output link ?

Question 3: Incoming traffic pattern

Queue Q1 receives the following packets (A is the first received packet) :

  • .E.D.C.B.A

Queue Q2 receives the following packets (a is the first received packet) :

  • ..e..d..c..b..a

Queue Q3 receives the following packets (0 is the first received packets) :

  • .....43210

Assuming the Q1-Q2-Q3 schedule, what are the first ten packets sent on the output link ?

Question 4: Incoming traffic pattern

Queue Q1 receives the following packets (A is the first received packet) :

  • .E.D.C.B.A

Queue Q2 receives the following packets (a is the first received packet) :

  • ..e..d..c..b..a

Queue Q3 receives the following packets (0 is the first received packets) :

  • .......210

Assuming the Q1-Q2-Q3 schedule, what are the first ten packets sent on the output link ?