Understanding the 7 Layers of the OSI Model

Posted on Feb 27, 2025 in Contemporary Music Composition

Levels of the OSI Model

  • Application
  • Presentation
  • Session
  • Transport
  • Network
  • Data Link
  • Physical

Description of the Seven Layers

Physical Layer

Defines the communication medium for the transfer of information, controls this environment, and specifies control bits by:

  • Defining physical connections between computers.
  • Describing the mechanical aspect of the physical interface.
  • Describing the electrical aspect of the physical interface.
  • Describing the functional aspect of the physical interface.
  • Defining the art of transmission.
  • Defining the type of transmission.
  • Defining the line coding.
  • Setting transmission speed.
  • Setting operation mode line data.

Data Link Layer

This layer provides facilities for transmitting blocks of data between two network stations. It organizes the 1s and 0s of the physical layer into formats or logical groups of information. It is responsible for:

  • Detecting errors at the physical layer.
  • Setting an error detection scheme for broadcast or network reconfigurations.
  • Setting the access method that the computer should use to transmit and receive messages. The transfer of data across the physical link.
  • Sending data blocks necessary to control the timing.
  • Overall, this layer controls and interfaces with the network layer to inform it of error-free transmission.

Network Layer

This layer defines the routing and sending of packets between networks.

  • It is responsible for establishing, maintaining, and terminating connections.
  • This layer provides message routing, determining whether a particular message should be sent to Level 4 (Transport Layer) or Level 2 (Data Link).
  • This layer handles switching, routing, and congestion control of packets in a sub-network.
  • Defines the status of messages sent to network nodes.

Transport Layer

This layer acts as a bridge between the lower three levels (fully oriented to communications) and the top three levels (fully oriented to processing). It ensures reliable delivery of information.

  • Ensures that the arrival of network-level data has the transmission characteristics and quality of service required by Level 5 (Session).
  • This layer defines the physical location of network devices.
  • Assigns a unique address to each transport user.
  • Defines a possible multiplexing, meaning it can support multiple connections.
  • Sets out how to enable and disable the links between nodes.
  • Determines the protocol that guarantees the delivery of the message.
  • Sets data transparency and reliability in the transfer of information between two systems.

Session Layer

Provides services used to organize and synchronize dialogue between users and manage data exchange.

  • Sets the start and end of the session.
  • Handles recovery of the session.
  • Controls the dialogue, setting the order in which messages should flow between users.
  • References devices by name and not by direction.
  • Allows writing programs that run on any network installation.

Presentation Layer

Translates the format and syntax to assign the data for transmission on the network.

  • Determines the format of the data without bothering about its meaning or semantics.
  • Establishes independence for application processes, considering the differences in data representation.
  • Provides services to the application layer to interpret the meaning of the exchanged data.
  • Handles data exchange.
  • Handles data visualization.

Application Layer

Provides services to the user of the OSI model.

  • Provides communication between two application processes, such as application programs, network applications, etc.
  • Provides communication solutions for specific applications between network users: network management, file transfer protocol (FTP), etc.