The document discusses the web request and response lifecycle from DNS lookup through HTTP methods and status codes. It describes the process of DNS lookup involving the browser, operating system, resolving name server, root name server, top-level domain name server and authoritative name server to resolve a domain name like www.yahoo.com to an IP address. It then explains the stateless HTTP protocol and how it can deliver different types of data, as well as the TCP three-way handshake process for establishing a connection and transmitting data using windows and acknowledgements. The document also briefly mentions HTTP requests, responses, methods including safe and idempotent methods, and status codes.

1. Web request to
response life cycle
The session regarding dns lookup, tcp
handshake, http request, response,
methods, and status codes
Gopakumar K - Senior Software Engineer
Azmath Mohamad - Engineering Manager

2. DNS Lookup - www.yahoo.com
The following are included in the dns lookup process
Browser
Operating system
Resolving name server (ISP)
Root name server (.)
TLD Name server (com)
Authoritative name server (yahoo.com)

3. Conti...
If no cache
Request comes in for
www.yahoo.com.
Root Servers (.)
TLD Name Servers(com)
Authoritative Name Server
(yahoo.com)
Resolving name
server (ISP)
End user PC
Web Browser
98.139.183.24 (www.yahoo.com)
Cache

4. Http Protocol
Connectionless
Http can deliver any sort of data as long as (images, audio, videos ,
documents) the two computer are able to read it
Stateless
HTTP that utilizes TCP to transfer its information between Web servers and
clients
Wireshark is one of the software to test the protocol request response flow,
download url: https://www.wireshark.org/download.html

5. TCP Connection establishment(3 way handshake)
SYN: Synchronization
ACK: Acknowledgement

6. Conti..

7. Conti..
Flow-control mechanism requiring that source device receive an
acknowledgement from the destination
TCP uses expectational acknowledgement (Forward acknowledgement)
Window size determines the amount of data can transmit at one time before
receiving an acknowledgement
Larger window sizes increase communication efficiency
TCP window sizes are variable during the lifetime of a connection, it “Slides”
up and down based on network performance, so it is called sliding window.
Sender keeps a record of each data packet that it sends and expects an
acknowledgement.

8. TCP Closing connection

9. Http Request

10. Http Response

11. Http methods

12. Conti..
Safe Methods : Certain methods are specified to be safe, which means that executing
them will not modify the resource or have other side effects on the overall state of the
server. Unsafe methods may cause side effects, such as modifying a resource, sending an
email or initiating the processing of a credit card.
Idempotent Methods : Some methods are idempotent, meaning that executing identical
requests multiple times will have the same effect as executing only one request. For
example, DELETE requests are idempotent because once a resource is deleted it can't be
deleted again. Conversely, POST requests are not idempotent because a second POST
request may send a second email or process the same credit card a second time.By
definition, safe methods are also idempotent.

13. Http Status Codes

14. Conti..

15. Questions?