TCP/IP
What the TCP/IP Model Is
The TCP/IP model is basically OSI's simpler, real-world cousin. Same idea — layers, each with a job — but it collapses OSI's 7 layers into 4 layers.
Here's why it exists: OSI is the teaching model (great for understanding and troubleshooting), but TCP/IP is what the internet actually runs on. So the exam wants you to know both — and how they map to each other.
The 4 Layers
From top to bottom:
TCP/IP Layer | What it does |
|---|---|
Application | Everything users/apps touch (web, email, DNS) |
Transport | TCP/UDP, ports — reliable/fast delivery |
Internet | IP addresses, routing |
Network Access (a.k.a. Link) | Physical + MAC, cables, switches |
The Key Part — How It Maps to OSI
This is what the exam tests. TCP/IP layers are just OSI layers grouped together:
TCP/IP (4) | = OSI layers (7) |
|---|---|
Application | = Application + Presentation + Session (Layer 7,6,5) |
Transport | = Transport (Layer 4) |
Internet | = Network (Layer 3) |
Network Access | = Data Link + Physical (Layer 1, 2) |
See the pattern? TCP/IP just squishes OSI:
The top 3 OSI layers (7,6,5) all become one Application layer
Transport stays the same
Network becomes "Internet"
The bottom 2 OSI layers (2,1) become one Network Access layer
The Easy Way to Remember It
Middle two match up cleanly: Transport=Transport, and Internet=Network (just a name change)
Top squishes 3→1: Application swallows Presentation + Session
Bottom squishes 2→1: Network Access swallows Data Link + Physical
Flashcards:
How many layers in the TCP/IP model? → 4
Name the 4 TCP/IP layers (top→bottom) → Application, Transport, Internet, Network Access
TCP/IP Application layer = which OSI layers? → 7, 6, 5 (Application, Presentation, Session)
TCP/IP Network Access layer = which OSI layers? → 2, 1 (Data Link, Physical)
TCP/IP "Internet" layer = which OSI layer? → Layer 3 (Network)
Which TCP/IP layer maps 1:1 with OSI? → Transport (and Internet=Network by name)