P2P vs. Client-Server

Quantitative Comparison of P2P with Client-Server

Let’s calculate how long it will take to transmit a file from one server to a number of clients based on both the P2P and server-client architectures. The calculations will be performed based on the following givens.

• A server that can upload at a rate of $up_s$ where $up_s$ is the upload speed in bits/second.
• There are $N$ clients all wanting to download the same file from the server. Client $i$ can upload at a rate of $up_i$ bits/second and download at a rate of $dwn_i$ bits/second.
• The size of the file that all the peers want is $S$.

Client-Server

Let’s start with the client-server architecture. The following can be observed.

• Since $N$ clients each want a file of size $S$, the server will have to upload $NS$ bits. The upload rate of the server is $up_s$ so the server will take at least $\frac{NS}{up_s}$ time to transmit the file to all $N$ clients.
• The client with the lowest download rate ($dwn_{min} = min(dwn_i)$) will take at least $\frac{S}{dwn_{min}}$ time to download the full file.

So, in total the time taken to transmit the file will be the maximum of both of the times above, i.e.:

$$\max{\{\frac{NS}{up_s},\frac{S}{dwn_{min}} \}}$$