Purpose of OSI Model
The Open Systems Interconnection (OSI) model provides a conceptual framework for understanding and standardising the functions of a digital communication system without regard to their underlying internal structure and technology.
Layers of the OSI model and their roles
Each layer in the OSI model serves a specific function in the network communication process:
- 7 Application Layer:
Provides services directly to user applications, such as email, file transfer, and web. - 6 Presentation Layer:
Translates data formats, encrypts data, and ensures that data is readable by the application layer. - 5 Session Layer:
Establishes, maintains, and terminates communication sessions between devices. - 4 Transport Layer:
Ensures complete data transfer, maintains end-to-end connections, and provides reliable data transportation. It breaks up data from the session layer into segments before sending it to the Network layer. It manages error and flow control. Flow control manages speed of transmission. Error control ensures data transmitted is complete and requests retransmission if not. - 3 Network Layer:
Manages device addressing, tracks the location of devices on the network, and determines the best way to move data between networks. This layer breaks the segments into packets for transmission. - 2 Data Link Layer:
Provides node-to-node data transfer (which is between two devices on the same network), detects and possibly corrects errors that may occur in the Physical Layer. This layer breaks the packets into frames. - 1 Physical Layer:
Deals with the physical connection between devices, including the transmission media and signaling.
MAC Address Layer 2 Switching
Layer 2 switching involves the use of a device’s MAC (Media Access Control) address to forward data at the OSI layer 2 Data Link Layer. Switches operate at this layer by using MAC addresses to direct frames to the correct destination device within the same local area network (LAN).
IP Address Layer 3 Routing
Layer 3 routing is the function of routing packets to their destination network using logical addressing (IP addresses) at the OSI layer 3 Network Layer. Routers perform this task by examining the destination IP address in a packet’s header, maintaining a routing table and using this information to decide the best path for the packet to travel across interconnected networks.