Understanding TCP/IP and OSI Models

By Cephas Kamuchira on October 7, 2024

Beginner

Understanding TCP/IP and OSI Models will help you visualize how Network Protocols work together to establish Network connections among network devices and be able to exchange information. There are too many ways to understand TCP/IP and OSI Modules concept, the most known way is to compare or map the modules to Post Office’s departments since the Layers can be so similar to each other in terms of Routing, Packaging, and Processing functionalities.

So, mapping how the the Post Office’s Departments work all together to process a Letter or Package, will help you understand each Layer’s functions, however, I am not saying that it’s totally the same, but will make it easy to grasp the concept.

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TCP/IP and OSI in Brief

TCP/IP and OSI are hierarchical models to define how network devices and their applications must follow Protocols that have set of rules in order to communication with each other, similar to People Laws such a country Constitution.

Transmission Control Protocol/Internet Protocol (TCP/IP) Model was created by US Department of Defense (DOD) and Open Systems Interconnect (OSI) model was created by the International Standards Organization (ISO).

So, a Network Model such TCP/IP or OSI refers to comprehensive set of Protocols. Those protocols which are set of logical rules that Network devices must follow to communicate with each other. Protocols such HTTP, FTP, SMTP, POP3, OSPF, EIGRP, and ARP, just to name a few.

Important of TCP/IP and OSI Models

By understanding the TCP/IP and OSI models, you can imagine how TCP/IP protocols manage IP network flow.

On the downstream, how bits are sent by a network devices as electrical pulse across copper wires or pattern of light signals across fiber optic wires.
On the upstream how those bits received by a network device’s layer 1, reassembled into frame, de-encapsulated and re-encapsulated back again with New MAC address or switched to the right destination through the Ethernet switch.
On the Host/PC’s upstream, how those bits received from a switch or another Network device, disassembled the frame and the packet to verify if it’s meant to its MAC or IP address; how the Host/PC’s TCP/IP Stack breaks up the segment at the transport layer, responds with an acknowledgement (ACK), and sends the data up to the session, presentation, and application layers; and how every tiny communication requires this whole process to happen in a fraction of a second!

Pretty cool, huh? This process will make more sense to you after reading few articles of IP Fundamentals.

TCP/IP Suite Overview

Transmission Control Protocol/Internet Protocol (TCP/IP). The first part: TCP is a main protocol that runs under Transport Layer 4 of TCP/IP Model; IP is another main protocol that runs under Network Layer 3 of TCP/IP Model, hence, called TCP/IP Network Model – they just picked its name based on those protocols.

Both of them combined; refer to the whole suite or Networking Model that is used today for Network communication. OSI is similar to TCP/IP and used globally as reference Model since it has 7 layers vs. 5 Layers used by TCP/IP Model. But remember, we configure IPv4 or IPv6 stack on the Network devices instead of OSI stack.

The TCP/IP Networking Model defines and references a large collection of protocols that allow components to communicate. To help people understand a networking model (such TCP/IP and OSI Models), each model broken down to something called Layers. Each layer includes protocols and standards that relate to that category of functions and TCP/IP has two models as shown below.

The original TCP/IP Network Model started with 4 Layers

4. Application

3. Transport

2. Internet

1. Link Layer

The second version of TCP/IP became 5 layers: changed the name of Internet Layer to Network layer and divided the link Layer to 2 layers

5. Application

4. Transport

3. Network

2. Data-Link

1. Physical

The difference between OSI model and TCP/IP model: OSI stretched Application layer to 2 more layers:

7. Application

6. Representation

5. Session