edited by
4,049 views
5 votes
5 votes

Two ground stations are connected by a 10Mbps satellite link. The altitude of the satellite is 36,000km and the speed of the signal is 3x108 m/sec. What should be the packet size for channel utilization of 50% using GBN sliding window protocol. Window size is 100. Assume that the acknowledgement packets are negligible in size and there are no errors during communcations.

  1. 1.5 Kbytes
  2. 3 Kbytes
  3. 4.5 Kbytes
  4. 6 Kbytes
edited by

2 Answers

Best answer
7 votes
7 votes
Here the altitude of the satellite is 36,000km, i.e. $d=36000 \times 1000$ m

speed of the signal  $(v) = 3\times 10^8 m/s$

Propagation delay $T_p =\frac{2 \times 36000 \times 1000 }{3 \times 10^8} =0.24 s.$

(Packet must propagate to the satellite and then back)

Let packet size = L

bandwidth of channel B= 10Mbps

then transmission time $T_t =L/(10\times 10^6)$

$\text{Efficiency} = \frac{\text{Data transmitted}}{\text{Maximum data that could be transmitted}}$

In Go-Back-N, before first ACK comes, $N$ packets can be sent. ACK comes back after $T_t + T_p + T_p +T_{ack}$. $T_{ack} = 0$ as per question. So, we consider this time and during $T_t$ a packet of size $L$ can be sent. So,

$\text{Efficiency} = \frac{N \times L} { L + 2T_p \times B}$

$0.5 = \frac{100L}{L + 2\times 0.24 \times 10 \times 10^6}$

$0.5L + 2400000 = 100L$

$L = 2400000/99.5 = 24120.6 \text{ bits} \approx 3 \text{ Kbytes}$
selected by
2 votes
2 votes

=> (Efficiency) $\eta = \frac{N}{1 + \frac{4 * T_{P}}{T_{t}}}$

=> $\frac{1}{2} = \frac{100}{1 + \frac{4 * 12 * 10^{-2} * 10 * 10^{6}}{L}}$

=> L = $\frac{48 * 10^{5}}{199}$

=> L = 24120.6 bits = 3015 bytes = 3.015Kbytes ≌ 3Kbytes

Answer:

Related questions

1 votes
1 votes
1 answer
2
Anshul Shankar asked Jul 19, 2016
3,785 views
Adacency list is preferred over adjacency matrix when the graph is?A) planarB) DenseC) CliqueD) none of these
1 votes
1 votes
2 answers
3
rickeshjohn asked Dec 22, 2015
1,092 views
(a) Less number of cables are required(b) More number of cables are required(c) It is a distributed topology(d) Security is high
0 votes
0 votes
0 answers
4
Badayayash asked Jan 20, 2019
394 views
Is anyone giving made easy test series for 2019 gatei would like to discuss some questions.because i feel like there are many questions in the test series which are wrong...