TCP/IP Model
Internet Protocol Suite
The four-layer model the internet is actually built on. Leaner than the seven-layer OSI map, it is the practical organisation of the protocols that carry every packet you send.
The TCP/IP model — also called the internet protocol suite — is the four-layer framework that describes how the protocols running the real internet are organised. It is named after its two cornerstone protocols, TCP and IP, but it covers the whole family: UDP, HTTP, DNS, and more. Where the OSI model is the detailed teaching map, TCP/IP is the working blueprint your traffic genuinely follows.
The four layers
| Layer | Job | Protocols |
|---|---|---|
| Application | What apps speak to each other with | HTTP, DNS, SMTP, SSH |
| Transport | End-to-end delivery and ports | TCP, UDP |
| Internet | Addressing and routing across networks | IP, ICMP |
| Link | Local delivery over the physical medium | Ethernet, Wi-Fi, ARP |
How a request flows through it
Load a web page and the layers cooperate in order. The application layer forms an HTTP request. The transport layer (TCP) splits it into segments, adds port numbers, and guarantees ordered delivery. The internet layer wraps each segment in an IP packet with source and destination addresses and routes it across networks. The link layer puts the packet onto the local wire or radio, frame by frame. The destination reverses the sequence, each layer handing its payload up to the next.
Mapping to OSI
TCP/IP is essentially OSI compressed. The two models line up cleanly:
| TCP/IP | Maps to OSI layers |
|---|---|
| Application | Application + Presentation + Session (7, 6, 5) |
| Transport | Transport (4) |
| Internet | Network (3) |
| Link | Data Link + Physical (2, 1) |
The middle two layers match one-to-one, which is why the transport and network layers are described identically in both models.
Why it won
OSI was designed by committee as an ideal reference; TCP/IP grew out of working code that already connected real networks. Because it was simpler and actually deployed, TCP/IP became the foundation of the internet, while OSI survived as the vocabulary engineers use to discuss it. In practice you use both: you reason and troubleshoot with OSI's layer numbers, but the packets on your connection are organised by TCP/IP. Understanding the suite explains why, for example, a fast TCP download and a low-latency UDP game behave so differently despite sharing the same internet and link layers beneath them.