Networks Models

Devices on a network share info in a way that sticks to certain protocols. It is not just basic data shifting around. Those protocols break everything down into distinct layers. Every layer handles its own job. That setup makes the whole network easier to manage.

People use two key models to show how all this happens:

• The ISO/OSI model → It acts as a theoretical setup with seven layers. Folks often turn to it for studying or fixing problems.

• The TCP/IP model → This one serves as the real-world basis for the Internet. It has four layers in total.

The two models try to cover the same ground. They explain data traveling between devices. Still, they do it with varying amounts of detail.

The OSI Model

People still bring up the OSI model quite a bit. It stands for Open Systems Interconnection. They put it together back in the 1980s. The goal was to create a universal method for describing how computers share information with each other. The Internet does not follow the OSI model in a direct way. Even so, this model serves as a strong tool for grasping networks and breaking them down.

In the OSI model, communication passes through seven distinct layers. On the sending end, data travels from the highest layer all the way down to the lowest one. On the receiving end, the process flips around completely. The data moves back up through each layer step by step. It keeps going until it arrives at the application level.

1. Layer 1: Physical

   This layer sits at the very bottom. It deals with the hardware side of things. The layer sets out the medium used to carry raw bits, those basic 0s and 1s. Think of electrical signals or radio waves. Pulses of light in fiber optics count too. Ethernet cables serve as one example here. Wi-Fi signals work in the same way. Fiber optics provide another clear instance.

2. Layer 2: Data Link

   At this level, data gets organized into frames. Those frames then travel across the local network. Devices get identified through MAC addresses. Errors show up and get spotted right here. A switch forwarding frames between PCs on the same LAN offers a good example.

3. Layer 3: Network

   The Network layer handles routing data across different networks. It picks the best path from sender to recipient. Logical addresses come into play for that. The familiar IP addresses fit this description perfectly. A home router directing packets to a remote web server stands as a solid example.

4. Layer 4:

   TransportThis layer makes sure data arrives at its destination in a reliable fashion. It also keeps everything in the right order. Large data breaks down into smaller segments. Those segments reassemble once they reach the other side.

   • TCP provides reliable service. It checks to confirm all packets make it through.

   • UDP moves faster overall. Delivery comes with no guarantees though.

   TCP works well for downloading a file. UDP suits online gaming or video calls better.

5. Layer 5: Session

   The Session layer takes care of the back and forth between applications. It handles opening communication sessions. It keeps them going as needed. It closes them when done. Keeping a video call active until one user ends it gives a straightforward example.

6. Layer 6: Presentation

   Data gets translated at this layer. It might get encrypted or compressed too. All this happens so applications can make sense of it. SSL or TLS encryption in HTTPS connections serves as an example.

7. Layer 7: Application

   This layer sits right at the top. It stays closest to the user experience. Services go out to software like browsers or email clients. Chat apps rely on it as well. HTTP handles web browsing tasks. SMTP deals with email sending. DNS takes on domain resolution duties.

The TCP/IP Model

The TCP/IP model stands apart from the OSI one. It goes beyond theory. It actually forms the backbone of the modern Internet. This model relies on just four layers. That is fewer than the seven in OSI. The reason comes down to grouping some of those OSI functions into broader categories.

• Network Access Layer

  The network access layer deals with the physical side of sending data over the network. It lines up with the physical and data link layers from OSI. Take Ethernet or Wi-Fi as common examples here.

• Internet Layer

  The internet layer takes care of addressing and routing tasks. It mirrors the OSI network layer in that way. This layer sets the rules for how packets travel from one device to another across different networks. IPv4, IPv6, and ICMP serve as key protocols in this part.

• Transport Layer

  The transport layer works much like it does in OSI. It makes sure applications communicate reliably. That happens through protocols such as TCP or UDP.

• Application Layer

  The application layer pulls together roles from OSI's top three layers. Those include session, presentation, and application functions. Applications connect to the network right at this level. Protocols like HTTP, FTP, DNS, and SMTP operate here.

OSI vs TCP/IP

The two models complement each other:

• OSI model → a learning and troubleshooting tool, very detailed, helping network engineers identify issues (“Is it a Layer 3 problem?”).

• TCP/IP model → the practical framework used every day on the Internet.

You can think of it this way:

• ISO/OSI represents the theory side

• TCP/IP brings the practice. It runs the actual Internet systems we use.

Comparison Table

OSI Model (7 Layers)	TCP/IP Model (4 Layers)	Example Protocols
Application	Application	HTTP, FTP, SMTP, DNS
Presentation	Application	TLS/SSL, JPEG, MPEG
Session	Application	NetBIOS, RPC
Transport	Transport	TCP, UDP
Network	Internet	IP, ICMP, ARP
Data Link	Network Access	Ethernet, Wi-Fi (802.11)
Physical	Network Access	Cables, fiber, radio signals

Even though the OSI model is mostly theoretical, it helps us see how communication is structured step by step. The TCP/IP model, on the other hand, describes the real set of protocols that make the Internet work.