1. Role and Mechanism of Queue Internet Engineering

2. 1 What is Queue （ buffer ） Packet exchange ＝ Store – and – forward –Router temporary stores packet in buffer Packet is queued and then stored （ In Drop Tail ） earlier income packet will transmit soon, what comes in first is handled –If the queue overflows, packets will be dropped Router Queue （ buffer ）

3. Internet Engineering 2 Relationship between Node, Queue, Link Packet Queue (Buffer) LinkNode Node 0 Node 2Node 3Node 4 In NS2, each link has a queue Packets go through queue before sent out to the link If input rate is larger than output rate, overflow packets will be accumulated in queue –It can response to temporary traffic increase –Packet are dropped if queue length exceeds its capacity Bandwidth

4. Internet Engineering 3 Packet flow Observe the packet （ ID=62 ） （ % awk ‘$12==62’ out.tr ） ※ experiment １ - １ -(b): bandwidth 4Mbps Node 0Node 2Node 3Node 4 + 0.062 0 2 cbr 1000 ------- 0 0.0 4.0 62 62 - 0.062 0 2 cbr 1000 ------- 0 0.0 4.0 62 62 r 0.0682 0 2 cbr 1000 ------- 0 0.0 4.0 62 62 + 0.0682 2 3 cbr 1000 ------- 0 0.0 4.0 62 62 - 0.1302 2 3 cbr 1000 ------- 0 0.0 4.0 62 62 r 0.1522 2 3 cbr 1000 ------- 0 0.0 4.0 62 62 + 0.1522 3 4 cbr 1000 ------- 0 0.0 4.0 62 62 - 0.1522 3 4 cbr 1000 ------- 0 0.0 4.0 62 62 r 0.1584 3 4 cbr 1000 ------- 0 0.0 4.0 62 62 40Mbps 6ms 40Mbps 6ms 4Mbps 20ms 84ms 62ms 22ms Why?

5. Internet Engineering 4 Time for forwarding packet Node 0Node 2Node 3Node 4 40Mbps 6ms 40Mbps 6ms 4Mbps 20ms Queuing time in queue ＋ Forwarding time ＋ Time for transmission between links → (Queue length)×(Time for sending packet out) ※ Queue length ： the number of packet kept in queue, 31 in this ex → (Packet size [bytes])÷(Bandwidth of Link [Mbps]) 1000[bytes] 4[Mbps] → （ Link delay ） Time for sending packet from node 2 to node 3 62ms 2ms 20ms Total 84ms

6. Internet Engineering 5 Packet flow （ Dropped packet ） Observe packet （ ID=63 ） by （ % awk ‘$12==63’ out.tr ） ※ In experiment １ - １ -(b), bandwidth is 4Mbps Node 0Node 2Node 3Node 4 + 0.063 0 2 cbr 1000 ------- 0 0.0 4.0 63 63 - 0.063 0 2 cbr 1000 ------- 0 0.0 4.0 63 63 r 0.0692 0 2 cbr 1000 ------- 0 0.0 4.0 63 63 + 0.0692 2 3 cbr 1000 ------- 0 0.0 4.0 63 63 d 0.0692 2 3 cbr 1000 ------- 0 0.0 4.0 63 63 40Mbps 6ms 40Mbps 6ms 4Mbps 20ms Drop Dropped after join a queue

7. Internet Engineering 6 Experiment 2 Consider following relationship –Sending traffic rate –Bandwidth of bottleneck link –Queue length –Number of bytes discarded from queue 0 1 4 5 23 CBR/UDP Bandwidth: Bw (Bottleneck link) 40Mbps Queue Size: B

8. Internet Engineering 7 【 Supplement 】 Execution of Experiment 2 % ns problem2.tcl 1.0Mb 32 –out.tr out.nam out.queue out.udp are created % gnuplot gnuplot> l “problem2.gp” gnuplot> … gnuplot> set term post color gnuplot> set output “graph.ps” gnuplot> rep gnuplot> q If you don’t like the format, you can modify kadai1-2.gp (Bw)(B)(B)

9. Internet Engineering 8 【 Supplement 】 out.queue content out.queue (Trace file of queue) –$1 : time –$2, $3 : position of queue （ link ） –$4 : accumulated data in queue (queue length) [bytes] –$5 : accumulated packet number in queue [packets] –$6 : number of packets arrived to queue [packets] –$7 : number of packets sent out from queue [packets] –$8 : number of packets dropped by queue [packets] –$9 : amount of data arrived to queue [bytes] –$10 : amount of data send out from queue [bytes] –$11 : amount of data dropped by queue [bytes] ※ $5 ～ $11 is cumulative value from start of simulation

10. Internet Engineering 9 【 Supplement 】 out.udp content out.udp (Trace file of UDP) –$1 : time –$2 : send traffic rate [Mbps] –$3 : bandwidth of bottleneck link [Mbps]

11. Internet Engineering 10 Example of graph （ attention point ） ※ In experiment 2 when Bw is 1.0Mbps and B is 32kbytes 31