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DAY 12 – ENCAPSULATION IN OSI MODEL AND TCP/IP PROTOCOL SUITE-

1) ENCAPSULATION IN OSI MODEL – DEFINITION
Encapsulation is the process of adding headers (and sometimes trailers) to data as it moves down the OSI layers at the sender side. Each layer adds its own control information.

At the receiver side, the reverse process is called Decapsulation.

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2) DATA FLOW IN OSI MODEL (SENDER SIDE)

Application Layer:
User creates data (Message)

Presentation Layer:
Formats, encrypts, compresses data

Session Layer:
Adds session information

Transport Layer:
Adds Transport Header
Segment is formed
Header contains:
Source Port
Destination Port
Sequence Number

Network Layer:
Adds IP Header
Packet is formed
Header contains:
Source IP
Destination IP

Data Link Layer:
Adds Frame Header and Trailer
Frame is formed
Header contains:
Source MAC
Destination MAC
Trailer contains:
Error detection (CRC)

Physical Layer:
Converts frame into bits and transmits

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3) ENCAPSULATION SUMMARY TABLE

Layer Data Unit Name
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Application Data
Transport Segment
Network Packet
Data Link Frame
Physical Bits

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4) DECAPSULATION (RECEIVER SIDE)

Physical → Data Link → Network → Transport → Session → Presentation → Application

Each layer removes its corresponding header and passes remaining data upward.

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5) TCP/IP PROTOCOL SUITE – DEFINITION

TCP/IP (Transmission Control Protocol / Internet Protocol) is a practical networking model used in the Internet.

It consists of four layers.

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6) TCP/IP MODEL LAYERS

Application Layer
Combines OSI Application, Presentation, Session
Examples:
HTTP, HTTPS, FTP, SMTP, DNS

Transport Layer
Provides end-to-end communication
Protocols:
TCP – Reliable
UDP – Unreliable

Internet Layer
Handles logical addressing and routing
Protocol:
IP (IPv4, IPv6)

Network Access Layer
Handles physical transmission and MAC addressing
Examples:
Ethernet, ARP

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7) COMPARISON: OSI VS TCP/IP

OSI Model:
7 layers
Conceptual model
Developed by ISO

TCP/IP Model:
4 layers
Practical model
Used in Internet

Layer Mapping:

OSI Layer TCP/IP Layer
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Application Application
Presentation Application
Session Application
Transport Transport
Network Internet
Data Link Network Access
Physical Network Access

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8) KEY DIFFERENCE BETWEEN TCP AND UDP

TCP:
Reliable
Connection-oriented
Error checking
Slower

UDP:
Unreliable
Connectionless
Faster
No guaranteed delivery