Bob and Alice are users of a P2P filesharing application The

Bob and Alice are users of a P2P file-sharing application. Their first-hop routers are R1 and R2 respectively Assume the transmission rate achieved is 2.5Mbps downstream for Bob, 2.5Mbps upstream for Alice, and 5 Mbps from R1 to R2. The end-toend path is 2000Km long; the propagation speed is 2.5*108 m/sec. The initial handshake has been completed. Bob’s P2P application starts to download a 500KB file from Alice’s machine. Ignore packet header and processing delays. Packet size is 1KB and packets are sent from Alice’s machine to the network back-to-back. If all links are lightly loaded (i.e., there is no queueing delay), how long does it take to download the file? Hint: you may assume all three links are of the same length.

Solution

so this will have 4 time components --

1. uploading time from alice\'s computer = (500/1024)*(8/2.5) seconds

2.R1 to R2 -> twice of time taken at one router that is--

(500/1024)*(8/5)

3.downloading time on bob\'s computer = (500/1024)*(8/2.5) seconds

4. transmission delay= (2000*10³)/(2.5*10⁸)=2/250 seconds

Add them --

you will get = 3.91425 seconds