How long does it take a packet of length 1,000 bytes to propagate over a link of distance 2,500 km, propagation speed 2.5 · 108 m/s, and transmission rate 2 Mbps?

More generally, how long does it take a packet of length L to propagate over a link of distance d, propagation speed s, and transmission rate R bps?

Does this delay depend on packet length?

Does this delay depend on transmission rate?

a) tp = 10 msec. b) = d/s c) No d) No

Explanation:

a) The propagation time for a packet of L bytes, over a link with a transmission rate of R bps, is given by the relationship between the distance traveled, and the propagation speed across the physical medium, assumed to be constant, as follows:

s = Δx/Δt ⇒ Δt = Δx/s

In our case, we know that Δx=d=2.5*10³ km = 2.5*10⁶ m, and that s = 2.5*10⁸ m/s, so replacing in (1), we get:

tp = Δt = 2.5*10⁶ m / 2.5*10⁸ m/s = 10⁻² sec. = 10 msec.

b) As stated above, the propagation time (not the total delay time that involves the transmission delay also) is given by a fixed relationship, as follows:

tp = Δx/v = d/s

c) As stated above, the propagation delay does not depend on packet length.

d) As stated above, the propagation delay does not depend on transmission rate.