Official PYQ · 2012Q44Concept of Layering: OSI and TCP/IP Protocol StacksMCQ1 mark

GATE CS 2012 Q44 — Concept of Layering: OSI and TCP/IP Protocol Stacks

Consider a source computer $(S)$ transmitting a file of size $10^{6}$ bits to a destination computer $(D)$ over a network of two routers $(R_{1}\text{ and }R_{2})$ and three links $(L_{1},L_{2},\text{ and } L_{3})$ . $L_{1}$ connects $S$ to $R_{1}$ ; $L_{2}$ connects $R_{1}$ to $R_{2}$ ; and $L_{3}$ connects $R_{2}$ to $D$ . Let each link be of length $\text{100 km}$ . Assume signals travel over each link at a speed of $10^{8}$ meters per second. Assume that the link bandwidth on each link is $\text{1 Mbps}$ . Let the file be broken down into $1000$ packets each of size $1000$ bits. Find the total sum of transmission and propagation delays in transmitting the file from $S$ to $D$ ?

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Answer: A

We can find the total time taken to transmit the file using the store-and-forward packet switching model with $N$ packets and $k$ links.

1. Calculate individual delays:

Propagation delay per link ( $T_p$ ): $T_p = \frac{\text{Distance}}{\text{Speed}} = \frac{100 \times 10^3 \text{ m}}{10^8 \text{ m/s}} = 10^{-3} \text{ s} = 1 \text{ ms}$
Transmission delay per packet ( $T_t$ ): $T_t = \frac{\text{Packet Size}}{\text{Bandwidth}} = \frac{1000 \text{ bits}}{10^6 \text{ bps}} = 10^{-3} \text{ s} = 1 \text{ ms}$