Role and Mechanism of Queue Internet Engineering Internet

Role and Mechanism of Queue Internet Engineering

Internet Engineering What is Queue （buffer） n Packet exchange ＝ Store – and – forward Router Queue （buffer） – Router temporary stores packet in buffer n n 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 1

Internet Engineering Relationship between Node, Queue, Link Packet Node 0 n n n Queue (Buffer) Node 2 Link Bandwidth Node 3 Node 4 In NS 2, 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 2

Internet Engineering Packet flow 40 Mbps 6 ms Node 0 Why? 84 ms 62 ms 22 ms + r + r Node 2 0. 062 0. 0682 0. 1302 0. 1522 0. 1584 0 0 0 2 2 2 3 3 3 4 4 Mbps 20 ms cbr cbr cbr 1000 1000 1000 40 Mbps 6 ms Node 3 ---------------------------- 0 0 0 0 0. 0 4. 0 Node 4 62 62 62 62 62 Observe the packet （ID=62） （% awk ‘$12==62’ out. tr） ※experiment １ -１ -(b): bandwidth 4 Mbps 3

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

Internet Engineering Packet flow（Dropped packet） Drop 40 Mbps 6 ms Node 0 Node 2 4 Mbps 20 ms Node 3 40 Mbps 6 ms Node 4 Dropped after join a queue + r + d 0. 063 0. 0692 0 0 0 2 2 2 3 3 cbr cbr cbr 1000 1000 ---------------- 0 0 0. 0 4. 0 63 63 63 Observe packet（ID=63）by　（% awk ‘$12==63’ out. tr） ※In experiment １ -１ -(b), bandwidth is 4 Mbps 5

Internet Engineering Experiment 2 0 4 CBR/UDP 40 Mbps Queue Size: B 2 Bandwidth: Bw 3 (Bottleneck link) 1 n 5 Consider following relationship – – Sending traffic rate Bandwidth of bottleneck link Queue length Number of bytes discarded from queue 6

Internet Engineering 【Supplement】 Execution of Experiment 2 % ns problem 2. tcl 1. 0 Mb 32 (Bw) (B) – out. tr out. nam out. queue out. udp are created % gnuplot> l “problem 2. gp” gnuplot> … gnuplot> set term post color gnuplot> set output “graph. ps” gnuplot> rep gnuplot> q n If you don’t like the format, you can modify kadai 1 -2. gp 7

Internet Engineering 【Supplement】 out. queue content n 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 8

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

Internet Engineering Example of graph（attention point） 31 ※In experiment 2 when Bw is 1. 0 Mbps and B is 32 kbytes 10