In the world of computer networking, understanding the foundational models is crucial for grasping how data travels across the internet. The TCP/IP and OSI models are essential frameworks that describe how networks function and communicate.

While both models serve similar purposes, they have distinct structures and applications. Whether you're a networking pro or just curious, this overview will help you understand these key protocols.

 In the 1970s, when companies started inventing protocols, most were proprietary. For two devices to “talk,” they must support the same protocol. Throughout the 1970s and 1980s, there was debate about which protocol would be the best for networking.

The Open Systems Interconnect Model (OSI Model) started in the 1970s. It was adopted as a working model by the International Organization for Standardization (ISO) in the 1980s. The idea was to make a standard reference model that could be used to invent protocols that would be compatible.

 The Transmission Control Protocol/Internet Protocol Model (TCP/IP Model) was released in 1981. TCP/IP Model was based on a different, four-layer model. Since TCP/IP Model was in use on the Internet, its popularity edged out OSI Model protocols.

Today OSI Model is used for reference. It supplies a great description of how protocols work.

TCP/IP model

TCP/IP model - the suite of TCP/IP protocols that are used for internet communications. It is a method of visualizing the interactions of the various protocols that make up the TCP/IP protocol suite.

It defines four categories of functions:

  1. Application - Represents data to the user, encoding and dialog control
  2. Transport - Supports communication between various devices across diverse networks
  3. Internet - Determines the best path through the network
  4. Network Access - Controls hardware devices and media that make up the network.

OSI model

OSI model - internetwork reference model created by the Open Systems Interconnection (OSI) project at the International Organization for Standardization (ISO).

  • Application layer 7 - protocols used for process-to-process communications.
  • Presentation layer 6 - common representation of the data transferred between application layer services (compression and encryption).
  • Session layer 5 - services to the presentation layer to organize its dialogue and to manage data exchange.
  • Transport layer 4 - services to segment, transfer, and reassemble the data for individual communications between the end devices (error correction).
  • Network layer 3 - services to exchange the individual pieces of data over the network between identified end devices (logical addressing: IPv4; IPv6).
  • Data Link layer 2 - methods for exchanging data frames between devices over a common media that include exchanging frames, controlling media access, and performing error detection (physical addressing).
  • Physical layer 1 - the mechanical, electrical, functional, and procedural means to activate, maintain, and de-activate physical connections for a bit transmission to and from a network device layer.

How the OSI Model relates to the TCP/IP Model and the protocols that make up the TCP/IP protocol suite

   OSI Model  TCP/IP Model  Protocols
 7  Application layer  Application layer  HTTP, HTTPS, SMTP, IMAP, POP, NFS, DNS, SNMP, DHCP, FTP, TFTP, Telnet
 6  Presentation layer
 5  Session layer
 4  Transport layer  Transport layer  TCP, UDP
 3  Network layer  Internet layer  IPv4, IPv6, ICMP, IGMP, ARP, RIP, OSPF, EIGRP, BGP, IPSec, NAT
 2  Data Link layer  Network layer  Ethernet (CSMA/CD, CSMA/CD), Token Ring, PPP, L2TP, PPTP
 1  Physical layer

 

OSI Layers 1 (Physical), and 2 (Data Link) map to the TCP/IP Network Access layer.

OSI Network Layer 3 maps to the TCP/IP Internet layer.

This layer describes protocols that address and route messages through the internetwork.

OSI Transport Layer 4 maps to the TCP/IP Transport layer.

This layer describes general services and functions that provide sequential and reliable delivery of data between source and destination hosts.

OSI Layers 5 (Session), 6 (Presentation), and 7 (Application) map to the TCP/IP Application layer.

The TCP/IP application layer consists of several protocols with specific functionality for end-user applications.

If you need a way to remember the OSI Model, there are popular phrases.

  • From the top down, All People Seem To Need Data Processing.
  • From the bottom up, Please Do Not Throw Sausage Pizza Away.
  • From the bottom up, Please Do Not Tell Secret Password Anyone.