# UGCNET-June-2019-II: 83

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You are designing a link layer protocol for a link with bandwidth of $1$ Gbps ($10^9$ bits/second) over a fiber link with length of $800$ km. Assume the speed of light in this medium is $200000$ km/second. What is the propagation delay in this link?

1. $1$ millisecond
2. $2$ milliseconds
3. $3$ milliseconds
4. $4$ milliseconds

edited

Propagation delay : Time taken by the first bit to travel from sender to receiver end of the link.

Propagation delay = distance/transmission speed = d/s

Propagation delay = 800km/200000km/sec

=4ms

1 sec =1000 mil sec

and propagation delay=distance/velocity

here distance=800 km and velocity=200000 km/sec

so, Tp=800/200000=1/250 sec

1/250 *1000=4 mil sec

Propagation delay : Time taken by the first bit to travel from sender to receiver end of the link.

Propagation delay = distance/speed of the medium = d/s

Propagation delay = 800km/200000km/sec

=(800/200000)sec

=(800/200)milliseconds

=4 milliseconds

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