Encapsulation

Encapsulation is the process of wrapping data by adding headers as it passes through each layer. On the way down each layer stamps its own signature onto the packet; at the destination each layer peels its header back off.

Duration

4min

Level

Type

Lesson

Progress

5/ 6

01Data transformation

As data moves from the application layer down to the physical layer, it changes its name and structure:

L7 · Application

DATA

L4 · Transport

TCP

DATA → Segment

L3 · Network

TCP

DATA → Packet

L2 · Data Link

ETH

TCP

DATA

FCS

L1 · Physical

101010101010... → Bits

02What each layer adds

Layer	Unit	Added
Application	Data	Application payload
Transport	Segment	TCP/UDP header (Port)
Network	Packet	IP header (IP address)
Data Link	Frame	MAC header + FCS trailer
Physical	Bits	Electrical signals

03Header contents

TCP Header (Transport Layer)

TCP

Transport Control Protocol Header

The transport layer header carries everything needed to guarantee reliable delivery.

Fields

Source Port · 16 bit Dest Port · 16 bit Sequence No Ack No Flags: SYN ACK FIN Checksum

Purpose

Which application? → Port
Packet lost? → Sequence No
Connection open? → Flags

IP Header (Network Layer)

Internet Protocol Header

The network layer header identifies the packet's origin, destination, and how it should be routed.

Fields

Source IP · 32 bit Dest IP · 32 bit TTL Protocol (TCP=6)

Purpose

Where to? → Destination IP
Where from? → Source IP
Prevent routing loops → TTL

04De-encapsulation

The reverse happens at the destination — each layer strips its own header:

L2 · Data Link

ETH

TCP

DATA

FCS

L3 · Network

TCP

DATA — ETH header removed

L4 · Transport

TCP

DATA — IP header removed

L7 · Application

DATA — Delivered to application

05Why encapsulation?

Modularity — Each layer works independently
Flexibility — Changing one layer doesn't affect the others
Error control — Each layer checks its own errors

06Summary

Encapsulation = Wrapping at each layer on the way down
Each layer adds its own header
Data → Segment → Packet → Frame → Bits
De-encapsulation unwraps headers at the destination

Encapsulation

Duration

4min

Level

Type

Lesson

Progress

5/ 6

01Data transformation

As data moves from the application layer down to the physical layer, it changes its name and structure:

L7 · Application

DATA

L4 · Transport

TCP

DATA → Segment

L3 · Network

TCP

DATA → Packet

L2 · Data Link

ETH

TCP

DATA

FCS

L1 · Physical

101010101010... → Bits

02What each layer adds

Layer	Unit	Added
Application	Data	Application payload
Transport	Segment	TCP/UDP header (Port)
Network	Packet	IP header (IP address)
Data Link	Frame	MAC header + FCS trailer
Physical	Bits	Electrical signals

03Header contents

TCP Header (Transport Layer)

TCP

Transport Control Protocol Header

The transport layer header carries everything needed to guarantee reliable delivery.

Fields

Source Port · 16 bit Dest Port · 16 bit Sequence No Ack No Flags: SYN ACK FIN Checksum

Purpose

Which application? → Port
Packet lost? → Sequence No
Connection open? → Flags

IP Header (Network Layer)

Internet Protocol Header

The network layer header identifies the packet's origin, destination, and how it should be routed.

Fields

Source IP · 32 bit Dest IP · 32 bit TTL Protocol (TCP=6)

Purpose

Where to? → Destination IP
Where from? → Source IP
Prevent routing loops → TTL

04De-encapsulation

The reverse happens at the destination — each layer strips its own header:

L2 · Data Link

ETH

TCP

DATA

FCS

L3 · Network

TCP

DATA — ETH header removed

L4 · Transport

TCP

DATA — IP header removed

L7 · Application

DATA — Delivered to application

05Why encapsulation?

Modularity — Each layer works independently
Flexibility — Changing one layer doesn't affect the others
Error control — Each layer checks its own errors

06Summary

Encapsulation = Wrapping at each layer on the way down
Each layer adds its own header
Data → Segment → Packet → Frame → Bits
De-encapsulation unwraps headers at the destination