Computer-Networks

The propagation delay is the time it takes for the first bit to travel from the sender to the receiver (During this time the receiver is unaware that a message is being transmitted). The propagation speed depends on the physical medium of the link (that is, fiber optics, twisted-pair copper wire, etc.),

The round-trip time or ping time is the time from the start of the transmission from the sending node until a response is received at the same node. It is affected by packet delivery time as well as the data processing delay, which depends on the load on the responding node. If the sent data packet as well as the response packet have the same length, the round trip time can be expressed as:

Round trip time = 2 × Packet delivery time + processing delay
In case of only one physical link, the above expression corresponds to:

Link round trip time = 2 × packet transmission time + 2 × propagation delay + processing delay

Consider there is no effect of propagation delay and processing delay

round trip time ≈ 2 × packet transmission time

packet transmission time=round trip time/2=500/2= 250 ms
Transmission time= Message (bits) / band width (chanel capacity) = 1000 bits/50kbps =20 ms
Total time to receiver to receive the frame =250+20=270ms