OSI MODEL & TRANSMISSION TECHNOLOGIES

 

OSI Model – Introduction

Open system interconnection is abbreviated as OSI, which is a networking standard protocol suite. Before the development of the ISO model in the 1970s, every vendor was producing devices with their own standards which caused interoperability issues. Therefore, the international standardization organization felt a need for introducing a standard manufacturing model for all vendors. This was the basis for OSI model development to avoid interoperability issues.

Layers of the OSI Model

The beauty of the OSI model is this it covers the whole communication process from the end devices to other end devices. The whole communication process has been divided into seven layers. Each layer has its own function supporting communication.

Below are the seven layers of the OSI Model

·        Application Layer

·        Presentation Layer

·        Session Layer

·        Transport Layer

·        Network Layer

·        Data link layer

·        Physical Layer.

Functions Of OSI Layers

Each OSI layer is associated with a specific function for the delivery of data from source to destination.

Application Layer

This is the layer that provides an interface for the user to interact with an application that initiates a communication process.  We have a number of tasks that fall in the application layer like remote access of devices, resource sharing between machines, and the management of networks.

Presentation Layer

The presentation layer is the sixth layer in the list of OSI model layers. This layer is used to translate the user input to the machine language. It also performs the functions of data encryption and data compression for transmission.

Session Layer

The session layer is associated with establishing sessions between the source and destination. The job of establishing a session before data transfer and session termination upon data transfer is performed by the session layer. At the same time, this layer can establish multiple sessions with different destinations.

Transport layer

The transport layer is responsible for the successful and reliable delivery of data from the source to the destination. This layer works based on logical ports that are used to create sockets when combined with the IP address. Based on this socket, the data specified is differentiated.

Network Layer

The network is the third layer of this model which is used for logical addressing of network devices. Devices are addressed using the IP protocol and routers perform the function of packet forwarding after finding the location of devices in the networks.

Data Link Layer

This layer corrects the errors that occur at the physical layer and put the frames on the physical layer. This layer reads the MAC address and delivers frames in the Local Area Networks. This layer is further divided into the MAC layer and LLC.

Physical Layer

The physical layer is layer 1 that is referred to the physical devices in the network that carries traffic in the form of bits. The connectors, cables, and hubs are called layer 1 devices. This is the layer where devices are connected with each other.

 The functions of the seven layers have been summarized below showing their main functions against each layer

Transmission Technologies

Transmission is the process of sending signals between a source and a destination. Through these signals, information is transmitted in digital or analog format. Different type of protocols is used for this transfer of information like the modulation process demodulation, coding, decoding, multiplexing, and demultiplexing.

We have two main mediums of transmission that are

·        Wireless Media or Broadcast Networks

·        Wired media or point-to-point networks

 

Wireless Media or Broadcast Networks

This is a type of transmission technology where the data or information is transmitted over wireless media. There is no dedicated connection between the source and destination nodes. In this case, the data transmitted by one node is received by all other nodes. The requirement of information transfer in this type of communication is the reception of the signals transmitted by the main broadcasting device and the connecting devices are authenticated and a connection is made. After the connection is made the information can be exchanged.

The above figure shows a broadcast network where the router is a WI-FI router that generates signals which are received by the end devices and connectivity is established.

Wired /Point to Point Networks

In this technology, we have dedicated physical connections between devices. The data can be exchanged between these devices only. There may be intermediate devices connecting them, but this connection should be a physical cable, fiber, etc.

The point-to-point communication is established for sensitive data, which can be either voice, data, video, etc. but security bears great importance in this case.

Wired communication is also important when the bandwidth requirement is high as wireless signals may get weaker after going through certain obstructions 

The below figure shows how wired devices are connected.

Comparison between Wireless and Wired Technologies

Wired Technology	Wireless Technology
Physical Media Exist	No need of Physical media
No antenna is required	Antenna is required
Electrical or optical signals are sent	Electromagnetic waves are used.
More suitable for short-distance communication	Suitable for large distance communication
Less Complex for deployment	more complex for deployment
Supports high Bandwidth	Supports less Bandwidth
Less reliable, cable damage issues	Reliable, no damage issues
Faster than Wireless	Slower than wired technology