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OSI Model Cheat Sheet

The Open Systems Interconnection (OSI) model is a conceptual framework that divides network communication into seven layers. Each layer has a specific role, from transmitting raw bits over a physical medium to delivering data to end-user applications. Use this cheat sheet as a quick reference for layer names, functions, protocols, and data units.

OSI Model — 7 Layer Referencejustprotocols.comLayerNameFunctionProtocolsPDU7ApplicationLayer 7User-facing services & APIsHTTP, HTTPS, FTP, SMTP, DNS, SSH, SNMP, MQTTData6PresentationLayer 6Data format, encryption, compressionTLS/SSL, JPEG, MPEG, ASCII, JSON, XMLData5SessionLayer 5Session management & dialogsNetBIOS, RPC, PPTP, SIPData4TransportLayer 4End-to-end delivery & flow controlTCP, UDP, SCTP, QUICSegment / Datagram3NetworkLayer 3Routing & logical addressingIP, ICMP, IPsec, OSPF, BGP, ARPPacket2Data LinkLayer 2Framing & physical addressingEthernet, Wi-Fi (802.11), PPP, VLAN (802.1Q)Frame1PhysicalLayer 1Bits on the wire/airRS-232, RS-485, Ethernet PHY, USB, Fiber, DSLBit
The OSI (Open Systems Interconnection) model divides network communication into seven abstraction layers, from physical transmission (Layer 1) to user-facing applications (Layer 7).
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OSI vs TCP/IP Model

The OSI model has 7 layers and is primarily a teaching and reference framework. The TCP/IP model, which the internet actually uses, collapses these into 4 practical layers:

OSI Model (7 Layers)

  • 7 – Application → Application
  • 6 – Presentation → Application
  • 5 – Session → Application
  • 4 – Transport → Transport
  • 3 – Network → Internet
  • 2 – Data Link → Network Access
  • 1 – Physical → Network Access

TCP/IP Model (4 Layers)

  • Application HTTP, FTP, SMTP, DNS
  • Transport TCP, UDP
  • Internet IP, ICMP, ARP
  • Network Access Ethernet, Wi-Fi

Memory Aid

A popular mnemonic for remembering the OSI layers from Layer 1 (Physical) to Layer 7 (Application):

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  • Physical → Data Link → Network → Transport → Session → Presentation → Application

Related Protocol References

Dive deeper into the protocols referenced in the OSI model:

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