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Wrapping Data

Lesson 25 of 32 in Coddy's The OSI Model course.

As your message travels down the stack, each layer wraps it and the bundle gets a new name, its PDU (Protocol Data Unit):

  • Layers 5-7 hand around plain data
  • Layer 4 wraps it into a segment (TCP) or datagram (UDP)
  • Layer 3 wraps that into a packet
  • Layer 2 wraps that into a frame
  • Layer 1 transmits it all as bits

Using the right word signals instantly which layer you are talking about, which is exactly how network engineers keep conversations unambiguous.

challenge icon

Challenge

Beginner

Print the five PDU names in the order the sender produces them, top of the stack first, one per line, lowercase.

Expected output:

data
segment
packet
frame
bits

Try it yourself

Terminal

All lessons in The OSI Model

1Why Layers

The Layering IdeaSeven LayersNumbers and NamesRecap - The Stack

4The Network Layer

IP and TTLPing and ICMPRouting TablesRecap - Layer Three

7Encapsulation

Wrapping DataHeaders EverywhereReading a CaptureRecap - Follow the Wrap

2The Physical Layer

Bits on a WireHow Long Will It TakeDuplex and Collisions

5Transport: TCP and UDP

PortsThe TCP HandshakeTCP vs UDPSockets in ActionRecap - Layer Four

8The Journey of a Packet

A Click HappensCrossing the NetworksArriving and ClimbingRecap - End to End

3Data Link and MACs

Frames and MACsReading a MACARPRecap - Layer Two

6The Upper Layers

Session and PresentationThe Application LayerWatching the LayersRecap - Top of the Stack

Practice on your own: Terminal playground