Question

2. A peer-to-peer system consists of a server (containing a copy of a file), and 20 peers. The file size is 10,000 bits, the upload rate of the server is 5,000 bits/sec., and the upload rate of each peer is 2,500 bits/sec. The download rate of each peer is 4,000 bits/sec. What is the minimum time required to distribute the file to all the peers under the peer-to-peer model ?

Answer 1

At time= 0 sec:

Let transfer file from server to two clients at equal speed of 2500bit/sec (5000/2).

So file will download by clients after 4sec

At time=4 sec

Now file is on server and two peers

So server can again send file two of new peers at equal speed of 2500bit/sec (5000/2).

And each peer can send the file to other peer at a speed of 2500.

So at 8sec, all files will be downloaded

At time =8sec:

Now file is on server and six peers

So server can again send file two of new peers at equal speed of 2500bit/sec (5000/2).

And each peer can send the file to other peer at a speed of 2500.

So at 12 sec, all files will be downloaded

At time =12sec:

Now file is on server and 14 peers

So server can again send file two of new peers at equal speed of 2500bit/sec (5000/2).

And each peer can send the file to other peer at a speed of 2500.

So at 16 sec, all files will be downloaded

Hence minimum time is 16sec.