OSI stands for Open Systems Interconnection Model
Layer 1 – Physical layer
- Defines physical media properties
- Electrical functions.
- Physical data rates.
- Physical connectors.
- Cable distances.
- Optical wavelength.
- Wireless frequency.
Typical layer 1 devices
- Cat5 cables
- Fiber optical cable
Layer 2 – Data link layer
- Defines data format for transmission. Eg: Ethernet, Frame Relay, PPP(Point to Point Protocol).
- Controls access to physical media. Eg: Ethernet CSMA/CD
- Defines physical addressing. Eg: Ethernet MAC address.
Typical layer 2 devices and protocols
- Wireless Access Point
Layer 3 – Network layer
- Provide connectivity and path selection. Eg: routing.
- Define local addressing / logical addressing. Eg: ipv4, ipv6.
Typical layer 3 devices and protocols
Layer 4 – Transport layer
- Breaks up data between sender and receiver into small parts called segmentation.
- Establish end to end connectivity.
- Can ensure reliable delivery.
- Error detection and re-transmission.
Typical layer 4 protocol
- Transmission control protocol (TCP)
- User datagram protocol (UDP)
Layer 5 – Session layer
- Manages session between end hosts.
- Eg: Web server tracking its open connections to web browser clients.
Layer 6 – Presentation layer
- Ensure that data can be understood between two end hosts.
- Eg: ASCII character encoding.
Layer 7 – Application layer
- Provide network service to the end host’s application.
- Eg: Email, FTP, Telnet.