Adding and removing headers and trailers to data as it is transmitted through the layers of the model
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Application Layer
Where users interact , on devices
Web browser: Chrome
Email clients: Microsoft Outlook
HTTP , FTP , SMTP
Whats app
Status codes
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Cookies
HTTP is stateless, so cookies is used to by browser to remember user data.
Cookie: A small text file stored on a user's device by a website, used to remember user preferences and activity.
Third party cookies
Third-party cookie: A cookie set by a domain other than the one that the user is currently visiting, used for tracking user behavior across different websites.
DNS (Domain Name System)
System that translates domain names (e.g. www.google.com) into IP addresses
DHCP is a network protocol used to dynamically assign IP addresses
Transport Layer
Guarantee the end to end delivery of data between application and server
Data in form of segments
TCP (Transmission Control Protocol)
Segment Numbering System
Connection oriented
Error control
Flow Control
Congestion control
Full Duplex : data can be sent in both directions at the same time.
UDP (User Datagram Protocol)
UDP (User Datagram Protocol) is a connectionless, unreliable transport protocol that allows for fast and efficient transmission of data packets over a network.
UDP is often used in scenarios where immediate delivery of data is more important than reliability
Unreliable : does not guarantee the delivery of data, and packets may be lost or delivered out of order
Connectionless : does not establish a connection before transmitting data.
No congestion control
Example :
Voice over IP (VoIP) like Skype or Zoom
Online Gaming
Streaming Media
Data packet in UDP , header + data
Data packet in UDP , header + data
Features
Features meaning
Multiplexing
TCP Congestion Control
Manage the rate at which data is transmitted over a network
Ensures that the sender does not overwhelm the receiver with data, causing packets to be dropped or delayed
Checksum
Extra data calculated from data using a math formula
If check sum at receiving end does not match the checksum sent with the data, data is corrupted and data should be retransmitted
TCP Timers
Retransmission timer: This timer is used by the sender to retransmit packets if they are not acknowledged within a specified time period.
Keep-alive timer: This timer is used by the receiver to ensure that the sender is still active and able to receive data.
3 Way Handshake
This could also be seen as a way of how TCP connection is established.
SYN (Synchronize) - Sender (client) sending a SYN message to the receiver (server) to initiate a connection request. This message contains a random sequence number that is generated by the sender
SYN-ACK (Synchronize-Acknowledge) - After receiving the SYN message, the receiver (server) responds with a SYN-ACK message. This message contains an acknowledgment of the sequence number sent by the sender and also a randomly generated sequence number
ACK (Acknowledgment) - The final step of the 3-way handshake involves the sender (client) sending an ACK message to the receiver (server). This message contains an acknowledgment of the sequence number sent by the receiver
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Network Layer
To find the optimal path for data packets to travel through the network
