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

$$2Mbps/100Kbps=20$$

2.b

$$0.2$$

2.c

$$\begin{gathered} X\sim B(N,0.1) \\ P(N,x)={\text{C}}_x^N\times p^x\times (1-p{)}^{N-x} \\ P(n)={\text{C}}_n^{40}\times p^n\times (1-p{)}^{40-n} \end{gathered}$$

2.d

$$\begin{gathered} P(n\ge 21)=1-P(n\le 20) \\ P(n\ge 21)=1-\sum _{x=0}^{20}P(x) \\ P(n\ge 21)=0.00000502 \end{gathered}$$

3.

$$\begin{gathered} delay(n)=\frac{Ln}{R} \\ \begin{array}{rl}\text{average delay}& =\frac{1}{N}\sum _{n=0}^{N-1}delay(n)\\ & =\frac{(N-1)\times L}{2R}\end{array} \end{gathered}$$

4.

$$\begin{array}{rl}\text{end to end delay}& ={\text{delay}}_{pro{c}_{4000km}}+{\text{delay}}_{trans}+{\text{delay}}_{queue}+{\text{delay}}_{pro{p}_{1000km}}+{\text{delay}}_{trans}\\ & =\frac{4000\times 10^3}{2\times 10^8}+\frac{1000\times 8}{2\times 10^6}+10^{-3}+\frac{1000\times 10^3}{2\times 10^8}+\frac{1000\times 8}{2\times 10^6}\\ & =(0.02+0.004+0.001+0.005+0.004)s\\ & =0.034s\end{array}$$

5.

Physical Layer:

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

Link Layer:

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.