OSI Model and Network Layers

Study Notes

Network Models: Layered Tasks

In sending a letter, layers are employed - sender, receiver, and carrier.
The carrier handles the delivery process, while the sender drafts and addresses, and the receiver ultimately receives the letter.
The post office acts as an intermediary, managing the different layers and ensuring the letter reaches its destination.

The OSI Model

Established by the International Standards Organization (ISO) in 1947.
The Open Systems Interconnection (OSI) model, introduced in the late 1970s, is a standard for communication protocols across networks.
This model utilizes a layered architecture, allowing devices to communicate at different levels.
Peer-to-peer processes within the OSI model mean that each layer interacts with its counterpart on the other device.
Encapsulation is the process of wrapping data in headers and trailers as it moves through the layers.

Layers of the OSI Model

Physical Layer: Deals with the physical aspects of network communication, including transmission medium, bit encoding, data rate, and synchronization.
- Physical characteristics of interfaces and the transmission medium.
- Representation of bits through encoding.
- Data rate or the number of bits transmitted per second.
- Synchronization of sender and receiver clocks.
- Line configuration, point-to-point or multipoint.
- Physical topology, how devices are physically connected in the network.
- Transmission mode, simplex, half-duplex, or full-duplex.
Data Link Layer: Focuses on reliable data transfer over a single network link.
- Framing, dividing data into manageable units called frames.
- Physical addressing for sender and receiver identification.
- Flow control, regulating the sending speed to avoid data overload.
- Error control, detecting and correcting errors across a single link.
- Access control, managing which device has control over the link at any given time.
Network Layer: Responsible for sending individual packets from the source to the destination.
- Logical addressing, adding addresses of the sender and receiver.
- Routing, determining the path for packets to reach their final destination.
Transport Layer: Ensures reliable delivery of messages between processes on different devices.
- Service-point addressing, finding specific processes or applications to communicate with.
- Segmentation and reassembly, breaking messages into smaller segments and putting them back together at the destination.
- Connection Control, offering either connectionless or connection-oriented communication.
- Flow control, regulating data flow between end devices.
- Error control, detecting and correcting errors across the entire network.
Session Layer: Manages communication sessions and ensures proper synchronization.
- Dialog control, managing the flow of information between devices.
- Synchronization, ensuring that data exchanged during a session is accurate and in the correct order.
Presentation Layer: Presents the data in a format that the application can understand.
- Data conversion, converting data from one format to another.
- Data encryption and decryption, securing the data during transmission.
Application Layer: Provides services to users and applications enabling them to interact with the network.
- User interface, providing a way for users to interact with the network.
- Network services, offering services to application, such as file transfer, email, and web browsing.