Host A and B are separated by single communication link of length m meters. Prop

Question

Host A and B are separated by single communication link of length m meters. Propagation speed of the link is s m/s and the data rate of the link is R bps. Consider the case where A sends a packet of length L bits to B. What is the propagation delay, d_prop, of the link? What is the transmission time, d_trans, of the packet? Ignoring the processing and queuing delays what is the end-to-end delay of the packet? If A starts transmitting at time t=0. Where is the last bit of packet at d_trans? If d_prop > d_trans where is the first bit of the packet at t= d_trans? If d_prop

Explanation / Answer

a)

distance between hosts A and B = m meters

propagation speed along th link = s meter/sec

so propagation delay = m/s or distance/s

b)

size of packet = L bits

and the transmission rate of the link = R bps

transmission of the packet = L/R sec

c)

end to end delay = d(proc) + d(queue) + d(trans) + d(prop)

= d(trans) + d(prop)

d(trans)= L/R and d(prop)=m/s

end to end delay = (L/R)+(m/s)

d)

transmission delay is time taken by host to push out the packet

so, at t = d(trans) the last bit of the packet has been pushed out or transmitted. ( The bit is just leaving Host A. )

e)

The first bit is in the link and has not reached Host B.

f)

if d(prop) < d(trans)

at time t = d(trans) the first bit has reached Host B.

g)

s = 2.5 x 10^8 sec

L = 100 bits

R = 28 kbps

d(trans) = d(prop)

so, (L/R)=(m/s)

distance m = sL/R

= (2.5×10^8×100)/(28×1000) = 892.8 km.

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