hw1 1. 1.b Repeat 1.a, but now with R3 reduced to 200 Kbps. 2. 2.a 2.b 2.c 2.d 3. 4. 5. Physical Layer: Link Layer: Network Layer: Transport Layer: Application Layer:

hw1

2023 computer-networking HW1.pdf

1.

Determine the bottleneck link, which is the link with the lowest throughput. In this case, the bottleneck link is the first hop with a throughput of 500 kbps.

1.b Repeat 1.a, but now with R3 reduced to 200 Kbps.

The bottleneck link is the first hop with a throughput of 200 kbps.

2.

2.a

2Mbps/100Kbps=202Mbps/100Kbps=20

2.b

0.20.2

2.c

X∼B(N,0.1)P(N,x)=CxN×px×(1−p)N−xP(n)=Cn40×pn×(1−p)40−nX\sim B(N, 0.1)\\ P(N,x)=\text{C}^{N}_{x}\times p^{x}\times(1-p)^{N-x}\\ P(n)=\text{C}^{40}_{n}\times p^{n}\times(1-p)^{40-n}\\

2.d

P(n≥21)=1−P(n≤20)P(n≥21)=1−∑x=020P(x)P(n≥21)=0.00000502P(n\geq 21)=1-P(n\leq 20)\\ P(n\geq 21)=1-\sum_{x=0}^{20}P(x)\\ P(n\geq 21)=0.00000502

3.

delay(n)=LnRaverage delay=1N∑n=0N−1delay(n)=(N−1)×L2Rdelay(n)=\frac{Ln}{R}\\ \begin{aligned}{} \text{average delay}&=\frac{1}{N}\sum_{n=0}^{N-1}delay(n)\\ &=\frac{(N-1)\times L}{2R}\\ \end{aligned}

4.

end to end delay=delayproc 4000km+delaytrans+delayqueue+delayprop 1000km+delaytrans=4000×1032×108+1000×82×106+10−3+1000×1032×108+1000×82×106=(0.02+0.004+0.001+0.005+0.004)s=0.034s\begin{aligned}{} \text{end to end delay}&=\text{delay}_{proc_{\ 4000km}}+\text{delay}_{trans}+\text{delay}_{queue}+\text{delay}_{prop_{\ 1000km}}+\text{delay}_{trans}\\ &=\frac{4000\times 10^3}{2\times 10^8}+\frac{1000\times 8}{2\times 10^6}+10^{-3}+\frac{1000\times 10^3}{2\times 10^8}+\frac{1000\times 8}{2\times 10^6}\\ &=(0.02+0.004+0.001+0.005+0.004)s\\ &=0.034s\\ \end{aligned}

5.

Physical Layer:

rincipal responsibilities: Hardware layer, such as cables, connectors, and network interface cards.

rincipal responsibilities: link two directly connected nodes, and the protocols that they use to communicate.

Network Layer:

rincipal responsibilities: provide the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks, while maintaining the quality of service functions.

Transport Layer:

rincipal responsibilities: transport data between two hosts, such as connection-oriented communication and connectionless communication.

Application Layer:

rincipal responsibilities: let application programs that use the network, such as web browsers, email clients, remote file access, etc.