Question

1. Suppose you request a webpage that contains 10 images. Suppose the transmission time for a webpage is 10ms, and the transmission time for an image is 5ms. Suppose that 10 images are located on 3 different servers: 5 of them are saved on marist.edu with the webpage, 2 are saved on nyu.edu, and 3 are saved on albany.edu.

Suppose the RTT between your host and marist.edu is 10 ms, between your host and nyu.edu is 20 ms, and between your host and albany.edu is 30 ms.

Assume parallel transmissions are not considered in this problem, that is, objects are obtained one after another.

a) How long does it take to load the entire webpage with HTTP 1.0?

b) How long does it take to load the entire webpage with HTTP 1.1?

Answer 1

SOLUTION:

The webpage is located on Server 1(marist.edu).

5 images are located on Server 1(marist.edu)

3 images are located on Server 2(nyu.edu)

2 images are located on Server 3(albany.edu)

The transmission time of a webpage=10ms.

The transmission time of an image=5ms.

RTT between host and marist.edu=10ms

RTT between host and nyu.edu=20ms

RTT between host and albany.edu=30ms

Now to load the entire webpage with HTTP 1.0
-------------------------------------------------------

You need to make 3 parallel connections, one with each server and maximum of time to transfer all required data from a server will be your time to load the entire webpage.

Time = 2*RTT for each object(RTT to make TCP connection and RTT to send file)+transmission time

Time to transfer data from marist.edu =2*RTT(1+5)+10+5*5=2*10*6+10+25=155ms

Time to transfer data from nyu.edu=2*RTT*2+2*5=2*20*2+10=90ms

Time to transfer data from albany.edu=2*RTT*3+3*5=2*30*3+15=195ms

Total time to load webpage =max(155,90,195)= 195 ms.

Now to load the entire webpage with HTTP 1.1
-----------------------------------------------------------------------

Time =RTT(TCP connection)+RTT for each object+transmission time.

Time to transfer data from marist.edu=RTT+RTT*(1+5)+10+5*5=10+10*6+10+25=105ms.

Time to transfer data from nyu.du=RTT+RTT*2+2*5=20+20*2+10=70ms

Time to transfer data from albany.du=RTT+RTT*3+3*5=135ms

Time to load webpage=max(105,90,135)=135ms.

Thank you,