Suppose there are exactly two packet switches (switch#1 and switch#2) between a sending host and a receiving host. The transmission rate between the sending host and switch#1 is R1, 200Mbps. The transmissions rate between switch#1 and switch#2 and between switch#2 and the receiving host are R2, 400Mbps and R3, 500Mbps, respectively. Assuming that the switches use store-and-forward packet switching, what is the total end-to-end delay to send a packet of length L, 1000 bytes? (Ignore queuing, propagation delay, and processing delay.)
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The total end-to-end delay to send a packet of length L can be calculated by summing the transmission delays at each switch.
At switch#1, the transmission rate is R1 = 200Mbps and the packet length is L = 1000 bytes. The transmission delay at switch#1 is therefore:
Transmission delay at switch#1 = L / R1 = 1000 bytes / 200Mbps
At switch#2, the transmission rate is R2 = 400Mbps. Since the packet has already been received from switch#1, the packet length remains the same (L = 1000 bytes). The transmission delay at switch#2 is:
Transmission delay at switch#2 = L / R2 = 1000 bytes / 400Mbps
At the receiving host, the transmission rate is R3 = 500Mbps. Again, the packet length is L = 1000 bytes. The transmission delay at the receiving host is:
Transmission delay at receiving host = L / R3 = 1000 bytes / 500Mbps
Finally, the total end-to-end delay is the sum of the transmission delays at each switch:
Total end-to-end delay = Transmission delay at switch#1 + Transmission delay at switch#2 + Transmission delay at receiving host
Total end-to-end delay = (L / R1) + (L / R2) + (L / R3)
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