OSI Model: Advantages and Disadvantages

This page discusses the advantages and disadvantages of the OSI Model, highlighting its benefits and drawbacks.

What is the OSI Model?

Introduction:

• The OSI (Open Systems Interconnection) model was conceived as a blueprint for universal communication standards, facilitating seamless interconnection between computers globally.
• The OSI model comprises seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application.
• The layer-based structure of the OSI model serves to define specific protocols, functions, and independent design and testing of components tailored to address particular classes of problems.

Image: OSI and TCPIP

Layer Breakdown:

• Physical: Primarily responsible for the transmission of bit streams over a physical medium (cable, air, etc.). It provides the hardware for sending and receiving data via wired or wireless connections.
• Data Link: Packages raw bits into frames, incorporating Cyclic Redundancy Checks (CRC) for error detection. It handles errors originating in the physical layer, manages flow control, and ensures frame synchronization. Automatic Repeat Request (ARQ) is implemented to facilitate retransmission in the event of packet errors. Media Access Control (MAC) addresses resource allocation to end devices seeking network connections for various applications (voice, data, etc.).
• Network: Primarily focuses on packet switching and routing. It adds logical addressing to accomplish this, while also managing error handling, congestion control, and packet sequencing.
• Transport: Ensures reliable data communication between two hosts. It handles error recovery and flow control between communicating devices and performs multiplexing and demultiplexing functions for transmitting and receiving hosts, respectively.
• Session: Provides a control mechanism for connecting two applications running on separate machines. Its core function is to establish, maintain, and release connections.
• Presentation: Formats and encrypts data for network transmission. Its main goal is to enable communication between the application and network layers by processing the data. It abstracts the application processes from data representation differences through syntax conversion.
• Application: This layer houses all user applications, including FTP, Telnet, and email.

Refer to the basics of OSI and TCP/IP layers for more comprehensive information.

Benefits or Advantages of the OSI Model

The following are the advantages of the OSI Model:

• It clearly differentiates between services, interfaces, and protocols. This allows devices from different vendors to operate together within a single network, unlike proprietary systems.
• Each layer defines a specific set of functions within data communication, which simplifies troubleshooting.
• The protocols within the OSI model are easily replaceable with new protocols and changes.
• The OSI model is a truly general model, easily adaptable by equipment/device manufacturers.
• This model supports both connection-oriented and connectionless services.

Drawbacks or Disadvantages of the OSI Model

The following are the disadvantages of the OSI Model:

• Many applications do not require the data integrity provided by the OSI model.
• The OSI model is excessively complex compared to TCP/IP, which is more optimized and efficient. The Session and Presentation layers are rarely used. The Data Link and Network layer functionalities are split into several layers.
• Connection mode transfer in the OSI model requires agreement between three parties (users and service provider), leading to slower operations.
• The OSI model is not universally adopted for all telecommunication applications used on computers.
• Due to the model’s complexity, initial implementations were time-consuming and slow.