OSI Layer Model

Ø Open System Interconnection (OSI) model is a conceptual model that covers all aspects of network communications.

Ø This model characterizes and standardizes the internal functions of a communications system by partitioning it into abstraction layers.

Ø This is a model that allows any two different systems to communicate regardless of their underlying architecture (hardware or software).

Benefits of OSI Model

v Reduces complexity.

v Standardizes interfaces.

v Facilitate modular engineering.

v Ensure interoperable technology.

v Simplify teaching and learning.

   

                                        OSI vs TPC/IP Models

                                   

Ø Physical Layer

The physical layer coordinates the functions required to transmit a bit stream over a physical medium. It also defines the procedures and functions that physical devices and interfaces have to perform for transmission occur. The physical layer is responsible for transmitting individual bits from one node to the next.

Ø Data Link Layer

Provides connectivity and path selection between two hosts. The data link layer is responsible for transmitting frames from one node to the next.

Ø Network Layer

Provide Reliable Transfer of data across media. The network layer is responsible for the delivery of packets from the original source to the final destination.

Ø Transport Layer

Concerned with Transportation issues between hosts. Establish. Maintain, terminate virtual circuits. The transport layer is responsible for delivery of a message from one process to another.

Ø Session Layer

Establishes, manages and terminates sessions between applications.

Ø Presentation Layer

Ensure data is readable by receiving system. Consider about format of data and structure of data.

Ø Application Layer

Provides network services to application processes. The application layer is responsible for providing services to the user.

  

Bandwidth

In computer networks, bandwidth is often used as a synonym for data transfer rate - the amount of data that can be carried from one point to another in a given time period (usually a second).

Ø Important of bandwidth

v Bandwidth is limited by physics and technology.

v Bandwidth is not free.

v Bandwidth requirements are growing at a rapid rate.

v Bandwidth is critical for network performance.

Ø Bandwidth Measurement

Network Layer

The Network layer is responsible for the source-to-destination delivery of a packet possible across multiple networks. If two systems are connected to the same link, there is usually no need for a network layer. However, if the two systems are attached to different networks, there is often a need for the network layer to accomplish source-to-destination delivery.