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The Layers of the OSI Model Illustrated
Each layer explained
By Bradley Mitchell Bradley Mitchell Writer Massachusetts Institute of Technology University of Illinois An MIT graduate who brings years of technical experience to articles on SEO, computers, and wireless networking. lifewire's editorial guidelines Updated on December 25, 2020 Reviewed by Jerrick Leger Reviewed by Jerrick Leger Jerrick Leger is a CompTIA-certified IT Specialist with more than 10 years' experience in technical support and IT fields. He is also a systems administrator for an IT firm in Texas serving small businesses. lifewire's editorial guidelines Tweet Share Email Tweet Share Email Home Networking The Wireless Connection Routers & Firewalls Network Hubs ISP Broadband Ethernet Installing & Upgrading Wi-Fi & Wireless The Open Systems Interconnection (OSI) model defines a networking framework to implement protocols in layers, with control passed from one layer to the next. It is primarily used today as a teaching tool. It conceptually divides computer network architecture into 7 layers in a logical progression. The lower layers deal with electrical signals, chunks of binary data, and routing of these data across networks. Higher levels cover network requests and responses, representation of data, and network protocols, as seen from a user's point of view. Lifewire / Colleen Tighe The OSI model was originally conceived as a standard architecture for building network systems, and many popular network technologies today reflect the layered design of OSI. Physical Layer
At Layer 1, the Physical layer of the OSI model is responsible for the ultimate transmission of digital data bits from the Physical layer of the sending (source) device over network communications media to the Physical layer of the receiving (destination) device. Lifewire / Colleen Tighe Examples of layer 1 technologies include Ethernet cables and hubs. Also, hubs and other repeaters are standard network devices that function at the Physical layer, as are cable connectors. At the Physical layer, data is transmitted using the type of signaling supported by the physical medium: electric voltages, radio frequencies, or pulses of infrared or ordinary light. Data Link Layer
When obtaining data from the Physical layer, the Data Link layer checks for physical transmission errors and packages bits into data frames. The Data Link layer also manages physical addressing schemes such as MAC addresses for Ethernet networks, controlling access of network devices to the physical medium. Lifewire / Colleen Tighe Because the Data Link layer is the most complex layer in the OSI model, it is often divided into two parts: the Media Access Control sub-layer and the Logical Link Control sub-layer. Network Layer
The Network layer adds the concept of routing above the Data Link layer. When data arrives at the Network layer, the source and destination addresses contained inside each frame are examined to determine if the data has reached its final destination. If the data has reached the final destination, layer 3 formats the data into packets delivered to the Transport layer. Otherwise, the Network layer updates the destination address and pushes the frame down to the lower layers. Lifewire / Colleen Tighe To support routing, the Network layer maintains logical addresses such as IP addresses for devices on the network. The Network layer also manages the mapping between these logical addresses and physical addresses. In IPv4 networking, this mapping is accomplished through the Address Resolution Protocol (ARP); IPv6 uses Neighbor Discovery Protocol (NDP). Transport Layer
The Transport Layer delivers data across network connections. TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are the most common examples of Transport Layer 4 network protocols. Different transport protocols may support a range of optional capabilities, including error recovery, flow control, and support for re-transmission. Lifewire / Colleen Tighe Session Layer
The Session Layer manages the sequence and flow of events that initiate and tear down network connections. At layer 5, it is built to support multiple types of connections that can be created dynamically and run over individual networks. Lifewire / Colleen Tighe Presentation Layer
The Presentation layer has the simplest function of any piece of the OSI model. At layer 6, it handles syntax processing of message data such as format conversions and encryption/decryption needed to support the Application layer above it. Lifewire / Colleen Tighe Application Layer
The Application layer supplies network services to end-user applications. Network services are protocols that work with the user's data. For example, in a web browser application, the Application layer protocol HTTP packages the data needed to send and receive web page content. This layer 7 provides data to (and obtains data from) the Presentation layer. Lifewire / Colleen Tighe Was this page helpful? Thanks for letting us know! Get the Latest Tech News Delivered Every Day Subscribe Tell us why! Other Not enough details Hard to understand Submit More from Lifewire Common Questions and Answers on the OSI Network Model Basic Computer Network Topics Explained Visually What Is a Switch? Computer Networking A Short Guide on Networking Fundamentals Here's Why Your Network Might Need a Layer 3 Switch An Overview of X.25 in Computer Networking OSI Model Reference Guide (With Examples) TCP/IP in Computer Networking How to Use the Netstat Command on Mac WAP (Disambiguation) - Wireless Access Point and More Task Manager (What It Is & How to Use It) What Is a Hub in a Computer Network? How Web Browsers and Web Servers Communicate NetBIOS: What It Is and How It Works What Is IPSec? How to Connect Chromecast to Hotel Wi-Fi Newsletter Sign Up Newsletter Sign Up Newsletter Sign Up Newsletter Sign Up Newsletter Sign Up By clicking “Accept All Cookies”, you agree to the storing of cookies on your device to enhance site navigation, analyze site usage, and assist in our marketing efforts. Cookies Settings Accept All Cookies