What this topic covers
8 subtopics- HTTP11
- HTTP performance10
- DNS9
- Architectures5
- Email5
- DHCP2
- FTP2
- HTTP versions1
- Beginner 15
- Intermediate 15
- Advanced 15
About this topic
The application layer is where networks meet users: DNS turns names into addresses, HTTP fetches the web, SMTP moves email and DHCP hands out addresses. Interviews ask "what happens when you type a URL"; GATE asks how many RTTs a page takes with persistent or non-persistent HTTP. Every response-time answer here was computed from the stated model, and the Python programs really ran.
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Sample questions
Try each one first, then open the answer for the explanation and why the other options are wrong.
What does DNS do?
Show answer and explanation
Explanation
Address assignment is DHCP, encryption TLS, routing the network layer.
Why the other options are wrong
- AThat is TLS.
- BThat is IP routing.
- DThat is DHCP.
A page has a base HTML file and 10 small images. With non-persistent HTTP and no parallel connections, how many RTTs does it take (ignore transmission time)?
The answer is a number – work it out, then open the solution.
Show answer and explanation
Explanation
Each of the 11 objects needs a new TCP connection (1 RTT) plus the request/response (1 RTT): 11 × 2 = 22 RTTs.
A page has a base file and 8 images, each 100 KB (8 × 10⁵ bits), over a 10 Mbps link with RTT 20 ms. Using persistent HTTP without pipelining (base file also 100 KB), what is the total time in ms?
The answer is a number – work it out, then open the solution.
Show answer and explanation
Explanation
Handshake 20 ms, then for each of 9 objects one RTT plus 80 ms of transmission: 20 + 9 × (20 + 80) = 920 ms.