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Consider the store and forward packet switched network given below. Assume that the bandwidth of each link is 106 bytes/ sec. A user on host A sends a file of size 103 bytes to host B through routers R1 and R2 in three different ways. In the first case a single packet containing the complete file is transmitted from A to B. In the second case, the file is split into 10 equal parts, and these packets are transmitted from A to B. In the third case, the file is split into 20 equal parts and these packets are sent from A to B. Each packet contains 100 bytes of header information along with the user data. Consider only transmission time and ignore processing, queuing and propagation delays. Also assume that there are no errors during transmission. Let T1, T2 and T3 be the times taken to transmit the file in the first, second and third case respectively. Which one of the following is CORRECT?
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- T1 < T2 < T3
- T1 > T2 > T3
- T2 = T3, T3 < T1
- T1 = T3, T3 > T2
- T1 < T2 < T3
Correct Option: D
I Transmission
1000 + 100 = 1100 bytes (transmitted from A at a time)
In 1 second → 106 bytes
| ∴ For 1100 bytes ⇒ 1100 × | = 8.8 m sec.(transmission time) | |
| 106 |
From A, R1 and R2 it takes T1 = 8.8 + 8.8 + 8.8 = 26.4 m sec. (to reach B)
II Transmission
100 + 100 = 200 bytes (transmitted 10 times from A)
| For 200 bytes ⇒ 200 × | = 1.6 m sec. | |
| 106 |
From A, transmission time to entire packet = 1.6 × 10 = 16 m sec.
From A, R1 and R2 it takes T2 = 16 + 1.6 + 1.6 = 19.2 m sec. (to reach B)
III transmission
50 + 100 = 150 bytes transmitted 20 times from A.
| For 150 bytes ⇒ 150 × | = 1.2 m sec. | |
| 106 |
From A, transmission time for entire packet = 1.2 × 20 = 24 m sec.
From A, R1 and R2 it takes T3 = 24 + 1.2 + 1.2 = 26.4 m sec. (to reach B)
∴ T1 = T3 = 26.4 m sec.
T2 = 19.6 m sec. < T3
