GATE CSE 2020 | Question: 25

Question

Assume that you have made a request for a web page through your web browser to a web server. Initially the browser cache is empty. Further, the browser is configured to send $\textsf{HTTP}$ requests in non-persistent mode. The web page contains text and five very small images.The minimum number of $\textsf{TCP}$ connections required to display the web page completely in your browser is__________.

Comments

Unless explicitly stated, don't think about HTML embedded images (even though "very small images" ideally could be embedded)

https://stackoverflow.com/questions/2807251/can-i-embed-a-png-image-into-an-html-page

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@js__ how 42 tcp ? do you mean each segment i.e syn is a tcp ?

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 @JHighlight 7 (3 connect + 4 disconnect)  *  6

Answer 1

In $\textsf{HTTP}$ non-persistent connection, each time a request is served by the server, the connection is automatically closed by the server.

So we need $1$ connection for web page and $5$ for images. Thus, in total we need $6$ $\textsf{TCP}$ connections to fetch web page completely.

Answer: 6

Comments

What if it is persistent mode ??

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Only 1 then.

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I have read somewhere that 1connection for html code is also required...is that true or not???

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Ah! I didn't think this way, very good solution

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its directly from forozan

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Suppose there are no images and nothing in the webpage only a single word. How many connection will be opened? That’ll be 1. So the text inside will count along with the webpage. So you need only 1 for the webpage not extra for the HTML code

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if Persistent connection then No. of connection required is 1 or 2 ???

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@Abhishek tarpara

 

if Persistent HTTP Connection is used, then No. of connection required is “ 1 “.

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using non-persistent connections, which are closed as soon as they are idle.but they did not mentioned about idleness of connection.

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If the “browser cache is NOT empty” then minimum number of TCP connections are $0 ?$

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Why do we have the phrase “browser Cache is empty”?

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What if it was asked “The total number of RTT’s required”?

Then ans should be 18. Is it correct ??

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2*Number of Images + 2 RTTs

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Means 12 RTT? but what about text?

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@Ayush Upadhayaya
In Non-persistent mode, one TCP connection for each request. “Client open TCP connection and sends a request then server will responds and closes the TCP connection”.
HTTP request also uses TCP.

So, Why not 7? Why 6??

1 connection for web page + 1 connection for text message
+ 5 connection for images = 7 TCP Connections.

correct me where i am wrong?

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@Ayush Upadhyaya sir, 

Here one connection for the webpages and 5 for the 5 different images so total 6 connection is required but my doubt is why aren't we consider the text file ? Can you please explain why for that we don't need separate connection?

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@Kabir5454

Web page contains “TEXT” which is written itself in base HTML file. So for extra 5 embedded images, 5 connections are required.

No where it is written that extra text file has to be fetched.

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Unable to understand what made Forouzan change the statement in the newer edition (5E). I am now confused about which one is correct.

 

 

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@Vishal The 5E edition is correct. Here is a snippet from Ross, reinforcing n+1 connections, +1 for the base HTML file.

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@Vishalkumar98

So , what’s the conclusion? for N files it will take N times connections or N+1  times connections?

and one more question!

here for text we are not considering any extra connection right? it will be included in the connection to fetch the webpage? or it's vice versa?

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 for N files it will take N times connections or N+1  times connections?

@Pranavpurkar

A web server will consist of different files, a file will contain different objects. When we open a new connection, we can access one of the files, but to fetch the objects inside the file we need new connections.

eg 1 file in a server has 10 objects, so we need one connection to establish a connection through port 80 and fetch that file, and then we need 10 extra connections to fetch the objects in the file. So a total of 11 connections are required.

For N files, it depends on the number of objects inside each file.

here for text we are not considering any extra connection right? it will be included in the connection to fetch the webpage? or it's vice versa?

Yes, we are not considering an extra connection for text because, if you have ever done web development you will see the text is contained inside the HTML file, but the images are actually stored inside the local directory or server, we just reference it in our HTML. That’s why we need a separate connection to fetch them.

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We'll require 15 RTTs as 3 to resolve DNS + 1 rtt for tcp + 1 for text and 10(2 each for 5 objects) =15

Answer 2

Since, Browser cache is empty, first of all DNS will complete its DNS translation, but that would be a UDP connection, so you don't need to worry about it!

After that, first TCP connection will be established which will be used to request the BASE HTML FILE. After the client extracts the base html file, it will Request for the five referenced objects of the pagr using five different TCP connections.

Hence, total 6 TCP connections would be required.

Comments

here the question mentions nonpersistent http , not necessarily non pipelined too ; which means it could be http 2.0 which allows sending multiple requests at once ;

so one connection for first base html ; another one for 5 images -> in total 2 connections ?

Answer 3

6

In non-persistent HTTP for every object there is a TCP connection required. Hence 1 TCP connection for text and 5 TCP connections for images required. So, total of 6 TCP connections are required.

Answer 4

🌐 Non-Persistent HTTP

• Behavior: Each HTTP request uses a separate TCP connection. Once the server sends the response, the connection is closed.

• Scenario:

  • 1 TCP connection for the base HTML (text).

  • 5 TCP connections for the 5 images.

• Total TCP Connections: 6

✅ Each object (HTML + 5 images) needs its own TCP connection.

🔗 Persistent HTTP

• Behavior: A single TCP connection is reused for multiple HTTP requests/responses.

• Scenario:

  • 1 TCP connection is established.

  • All 6 HTTP requests (1 for HTML + 5 for images) are sent over this single connection.

• Total TCP Connections: 1

✅ One connection handles all requests efficiently.

Answer 5

like this we have to establish the connection in non persistent connection so 1 connection for web browser and 5 connections for 5 images so total 6 s

for persistent we need to establish one time only

 

Answer 6

Non-Persistant : The web page has Text + 5 images so we need to make 6 HTTP requests (1 for page itself++ 5 for images) over separate TCP connection.

Persistant : Here also we need 7 HTTP requests but over single TCP connection.

 

Comments

why call to is not concidered DNS for IP resolution?

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Non-persistant 1st connection is established and the page is fetched and then then the conncection is broken and for the getting the image re connection is done so again HTTP request for each image.