TCP/IP model layers
The model
A protocol suite, layered like OSI, but these protocols actually run on real networks. It defines what host systems must provide, not how to implement it: guidance for vendors and implementors.
Four layers, many protocols. It’s named after just two, TCP and IP, because those layers do the heavy lifting for network communication. The industry shorthand is “IP stack”.
One line per layer:
- Application: represents data to users, handles encoding, controls the dialog.
- Transport: communication between end devices across diverse networks.
- Internet: logical addressing and best-path selection through the network.
- Link: controls the hardware and media that make up the network.
The four layers
Link
Also called the media access, network interface, network access, or data link layer. It interfaces with the directly connected network and is tied closely to the physical medium.
Many physical network types mean many link layer protocols; Ethernet is the big one. This layer introduces physical addresses (MAC, or hardware, addresses) to identify devices on the same physical segment.
Internet
Routes data from source to destination, learns how to reach other networks, and reports errors. Logical addressing means IP addresses: valid globally, uniquely identifying a host.
End devices (laptops, phones, servers) get an IP before joining the network. The protocols are IPv4 and IPv6. It serves the transport layer above and hands off to the link layer below.
Transport
The core of the architecture, sitting between the data movers (link and internet) and the software side (application). Two main protocols: TCP and UDP.
It prepares application data for transfer, tracks the transfer, and keeps different applications’ data separated. Each application gets its own addressing (ports), valid only locally within the host. Contrast with IP addressing, which is global.
Application
User-facing: the protocols and services that let you actually use the network, with network APIs so programs can reach network services regardless of OS.
Protocols: HTTP, HTTPS, DNS, FTP, SMTP, SSH, and plenty more. It covers web browsing, file transfer, name-to-IP resolution, email, and remote device access.
Quick recall
- Link = MAC addresses, local segment.
- Internet = IP addresses, global, IPv4/IPv6.
- Transport = TCP/UDP, ports (local to host).
- Application = HTTP(S), DNS, FTP, SMTP, SSH.