Understanding the Data Link and Physical Layers: The Final Step in Mastering OSI Model and Computer Networking

This is the eighth and final part of the computer networking series. Check out the previous parts if you haven't. In this part, we'll see about:

• Data Link Layer
  


• Physical Layer
  

Table of Contents

1. 
   Data Link Layer
   


2. 
   Physical Layer
   


3. 
   Conclusion
   

Data Link Layer

The data link layer is responsible for sending the data packets received from the network layer over a physical link.


In the data link layer, the data is sent as frames.

If many devices are connected in a LAN, the devices communicate with each other using their data link layer addresses.


If you don't know what a LAN is, we've already discussed it in a previous part. You can check it here ↓

Types of Networks and Topologies

Vignesh J ・ Nov 13

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Example of Communication in a LAN

Consider A, B, C, and D connected in a LAN, and A wants to send data to D:

1. 
   Checking ARP Cache:
   
   
   
   
   • First, A checks its cache memory (known as the ARP cache) for D's data link layer address.
     
   
   
   
   


2. 
   Broadcast Request:
   
   
   
   
   • If the address is unavailable, A sends a message to all devices in the network asking for D's data link layer address.
     
   
   
   • The message is a frame that includes:
     
     
     
     
     • The data link layer address of the sender (A).
       
     
     
     • The IP address of the destination (D).
       
     
     
     • A request for the data link layer address of the destination.
       
     
     
     
     
   
   
   
   

Address Resolution Protocol (ARP)

• 
  ARP Cache: Stores mappings of IP addresses to data link layer addresses.
  


• 
  MAC Address:
  
  
  
  
  • A unique 12-digit alphanumeric string that serves as the data link layer address.
    
  
  
  • Stands for Media Access Control.
    
  
  
  
  
  
  

The data link layer works closely with the physical layer to ensure communication.

Physical Layer

The Physical Layer is the bottom-most layer in the OSI Model. It represents the physical and electrical aspects of the system.

Key Features of the Physical Layer

1. 
   Hardware Components: Includes power plugs, connectors, receivers, and cable types.
   


2. 
   Transmission of Data Bits: Responsible for sending unstructured raw data streams from one device (e.g., a computer) to another.
   


3. 
   Encoding: Defines how 0s and 1s are encoded into signals for transmission over the physical medium.
   

The Physical Layer is responsible for communication over a physical medium like cables and wireless systems.

Conclusion

This marks the end of the OSI model and also the end of this series. I hope you’ve gained insights into some basic computer networking concepts necessary to understand how the internet works.

Remember, computer networking is a vast field with much more to explore. This series provides a foundational overview, but you can dive deeper into specialized topics by exploring additional resources.

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