quizz 2018 question 2 and quizz 2014 question 7

quizz 2018 question 2 and quizz 2014 question 7

par Jérémy Joël Weill,
Nombre de réponses : 4

Hello,

In these 2 questions, we need a number of RTTs twice bigger than the numbers of files we download. But, in the lecture it is said that the RTT is " the amount of time it takes for a small packet to go from one computer to the other and another small packet to return".

So, I am not sure to understand these answers because for me we should have the same number of RTTs than the number of files we download. Moreover, I am not sure to understand well what exactly represents the RTT here (is it the time to establish a TCP connection between the 2 end-systems?).

Thank you in advance for your response,

Jeremy

En réponse à Jérémy Joël Weill

Re: quizz 2018 question 2 and quizz 2014 question 7

par Katerina Argyraki,

Hi Jeremy,

Say a web browser wants to download a webpage from a web server. 

First, the transport layer on the web browser's computer establishes a TCP connection with the transport layer on the web server's computer. That takes at least 1 RTT.

Second, the web browser needs to get the base file from the web server. That takes at least another RTT.

If the base file references other, embedded files, e.g., images, then the web browser also needs to get those. (It's not necessarily true that, if the base file references N other files, it will take N*RTT to get those files, because the web browser may send all the get requests back to back. But that's another story, we can discuss it separately.)

Bottom line: at least 1 RTT to establish the TCP connection + at least 1 RTT to get the base file. That's why the answer is "at least 2 RTTs.

Does this make sense so far?

En réponse à Jérémy Joël Weill

quizz 2018 question 2 and quizz 2014 question 7

par Jérémy Joël Weill,
Yes it does.
So, if we have not a persistent TCP connection we'll need 2 RTTs per each embedded files?