Suppose a 128-kbps point-to-point link is set up between the Earth and a rover o

Question

Suppose a 128-kbps point-to-point link is set up between the Earth and a rover on Mars. The distance from the Earth to Mars (when they are closest together) is approximately 55Gm, and data travels over the link at the speed of light - 3 times 10^8 m/s. a) What is the one-way propagation delay of this link, in minutes? b) What is the transmission delay for a packet of 1500 bytes? c) How "wide" is a bit on this 128 kbps link? d) What is the total delay to send this 1500-byte packet from Mars to a Mission Control on Earth?

Explanation / Answer

a) Propagation Delay of the link is given as = (one side distance)/(Propogation Speed)

= (55 X 10^9) /(3 X 10^8 ) = 183.33 sec or 184 sec,

b) The transmission delay = N / R ,where N is the number of bits, and R is the rate of transmission

= (1500x8) /128000 sec

= 12000/128000 sec

= 0.09375 sec

c) How wide is a bit in 128kbps link = 128000 bits in one second

or = 1 bit in 1/128000 sec

or = 1 bit in 7.8125 sec

d.) Total delay = Transmission Time of 1500 byte data + Propagation delay

where, Transmission Time of 1500 byte data = (1500 x 8) bit x Transmission Time of 1 bit data

= 12000 bit x (1/128000) sec per bit

= 0.09375 sec

Hence, total time = transmission delay + propagation delay = 0.09375 sec + 183.33 sec

= 183.427 sec

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