Network Layers (5 Layer Model)
Layer 1 - Physical Layer
Lowest layer of the OSI model. It is responsible for the actual physical connection between the devices. It defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. It defines the relationship between a device and a physical transmission medium (e.g. copper, fiber, wireless).
Examples of physical layer specifications include:
- Voltage levels
- Timing of voltage changes
- Physical data rates
- Maximum transmission distances
- Physical connectors
- Pinouts
Layer 2 - Data Link Layer
Responsible for the reliable transfer of data between two adjacent nodes on a network. It provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the physical layer. It defines the protocol to establish and terminate a connection between two physically connected devices.
Examples of data link layer specifications include:
- Ethernet
- Wi-Fi
- PPP (Point-to-Point Protocol)
- HDLC (High-Level Data Link Control)
- ATM (Asynchronous Transfer Mode)
- Frame Relay
Layer 3 - Network Layer
Responsible for the delivery of packets from the source host to the destination host. It provides the functional and procedural means of transferring variable length data sequences from a source to a destination host via one or more networks, while maintaining the quality of service and error control functions.
Examples of network layer specifications include:
- IPv4
- IPv6
- ICMP (Internet Control Message Protocol)
- IGMP (Internet Group Management Protocol)
- ARP (Address Resolution Protocol)
Layer 4 - Transport Layer
Responsible for the delivery of a message from one process to another. It provides transparent transfer of data between end users, providing reliable data transfer services to the upper layers. It ensures complete data transfer.
Examples of transport layer specifications include:
- TCP (Transmission Control Protocol)
- UDP (User Datagram Protocol)
- QUIC (Quick UDP Internet Connections)
Layer 5 - Application Layer
Responsible for providing services to the user. It enables the user, whether human or software, to access the network. It represents the services that directly support user applications such as file transfer, electronic mail, and terminal emulation.
Examples of application layer specifications include:
- HTTP (Hypertext Transfer Protocol)
- FTP (File Transfer Protocol)
- SMTP (Simple Mail Transfer Protocol)
- DNS (Domain Name System)
- DHCP (Dynamic Host Configuration Protocol)