What are the 4 layers of the TCP IP model?

Layers of the TCP IP Model
Layers of the TCP IP Model

What are the 4 layers of the TCP IP model in networking?

The TCP IP model is a four-layer communication model that breaks down communication into manageable chunks. This makes it possible to standardize the process of communication without relying on software and hardware providers. As a result, companies can save time and money while still ensuring reliable communication. This post will look into all 4 layers of the TCP IP model in depth.

I would suggest you read about the OSI model, OSI model cheat sheet Infographic, IP subnettingVLANs, and VLAN tagged vs. untagged topics to grasp the basic understanding of networking.

What is TCP IP full form?

TCP/IP stands for Transmission Control Protocol/Internet Protocol. TCP IP reflects the two standard protocols in the model. The Transmission Control Protocol (TCP) manages end-to-end packet delivery, while the Internet Protocol (IP) provides IP addressing and Routing between networks.

What is a TCP IP model?  

The TCP/IP model is a conceptual model used to describe the functions of a networking system and how data travels from one device to another over a network. 

It is a hierarchical model which divides these functions into four abstraction layers which are Application, Transport, Internet, and Network Access layer respectively, and are used to describe the structure of communication networks. 

The TCP/IP model is often compared to the OSI model, which is a similar conceptual model for networking. The OSI model has 7 layers compared to 4 layers of the TCP IP model.

History of TCP IP model

Listed below are some key points that aided in the advancement of the TCP/IP model:

  • TCP IP protocol was developed by DARPA in the 1960s. 
  • In 1975, Stanford and University College London tested two-network TCP/IP communications.
  • In March 1982, the US Department of Defense declared TCP/IP as the standard for all military computer networking, which helped promote this model.
  • ARPANET adopted this structured protocol as a standard in 1983.
  • Companies like IBM, DEC, and others later adopted TCP/IP as their standard communication protocol.
  • The University of California accepted TCP/IP as public domain in 1989.
  • Slowly, the TCP/IP model became the global standard for computer networking and Internet communication.

What are the advantages and disadvantages of TCP IP?

Advantages of TCP/IP Model

There are many advantages of the TCP/IP model. 

  • It is a very flexible and scalable model and can be used in small, medium, and large networks.
  • TCP/IP is also a very reliable model. It is designed to be robust and handle a large amount of data without losing any information. 
  • It uses a modular approach, making it easy to add new features and services.
  • It uses a layered approach which makes it easy to understand and troubleshoot.
  • It supports many routing protocols.

Disadvantages of TCP/IP model

Some of the disadvantages of the TCP/IP model include:-

  • The TCP/IP model effectively gets a message from point A to point B. However, this model is not always the best choice. There are times when another model, for example, the OSI model, will be better suited in a particular situation.
  • Each layer of TCP/IP has its own set of protocols that govern how data is transmitted and received, which is sometimes difficult to understand and manage for newcomers.
  • The TCP/IP model is a logical model that doesn’t necessarily correspond to the network’s physical structure, which sometimes creates confusion.
  • TCP/IP model can sometimes be difficult to troubleshoot problems at each layer because of the complex interactions between the various protocols.

What are the 4 layers of the TCP IP model?

The TCP/IP reference model has four layers:

  1. Network Access Layer or Link Layer
  2. Internet Layer
  3. Transport Layer or Host to Host Layer
  4. Application Layer

Each layer is responsible for different aspects of communication. For example, the Network Access Layer is responsible for the physical transmission of data, while the Internet Layer handles routing and IP addressing. The Transport Layer ensures reliable communication between hosts, and the Application Layer provides services such as email and web browsing.

Network Access Layer or Link Layer

The Network Access layer is the first and the lowest layer of the TCP/IP model, and it combines the functionalities of the Physical Layer and the Data Link Layer of the OSI model.

The Network Access layer of the TCP/IP model uses Cables, Repeaters, Hubs, switches, and bridges to physically connect devices to the network and pass data within the same network subnet. The data unit is bits(1s and 0s) and frame. Protocols used on this layer are Ethernet, RS232, etc. 

The Network Access layer defines the mechanism for the physical transmission of data between devices on the same network. It defines how the data should be sent physically through a network and maps an IP address (4 bytes or 32 bits) into a physical address or MAC address (6 bytes or 48 bits). It includes hardware devices that directly interact with a network medium and identify hosts by utilizing the MAC address. This layer is mainly responsible for transmitting frames transmitted by a point-to-point connection, such as an ethernet cable or token ring cable.

What are the functions of the Network Access layer?

These are the functions of the Network Access Layer:-

  • Access to the physical network medium, like cables, wireless.
  • It provides MAC addressing and mapping of logical IP address to physical MAC address.
  • Error notification.
  • It does the sequencing of frames.
  • It provides Flow control.

Internet Layer

The Internet layer is the second layer of the TCP/IP model, and it is equivalent to the Network layer in the OSI model. Its primary function is to provide IP Addressing and Routing. Routers are used on this layer. The data unit is Packets, and protocols include IP protocol, ICMP, etc.

What are the functions of the Internet layer?

These are the functions of the Internet Layer:-

  • It is responsible for the source-to-destination delivery of a packet, including routing through intermediate routers across multiple network segments. 
  • The Internet layer is also responsible for the IP addressing scheme that uniquely identifies each host on a TCP/IP network.
  • The Internet layer also provides for fragmentation and reassembly of long datagrams.
  • The Internet layer also provides the Time-to-Live (TTL) field in the IP datagram header.
  • IP datagram also contains source and destination address which is used to forward packets between IP networks.
  • It also does error handling, congestion control, and QoS (Quality of Service).

Transport Layer or Host to Host Layer

The Transport layer is the third layer of the TCP/IP model and matches up to the Transport layer of the OSI model. It ensures data is delivered between applications in sequence,error-free, and without loss or duplication.

On this layer, firewalls are used. Its data unit is the Segment, and protocols are TCP and UDP.

TCP is a reliable, connection-oriented protocol that ensures that all data is delivered correctly. UDP is an unreliable, connectionless protocol that does not guarantee delivery or ensure that packets are received in order

It provides reliable, in-order delivery of packets to endpoints on a network. This layer ensures that messages are delivered correctly and that all packets arrive in the correct order. In addition, it can multiplex and demultiplex data streams between two applications.

What are the functions of the Transport Layer?

  • The Transport layer chops the message received from the Application layer into segments and tags or numbers them to make a sequence. And then forwards it to the IP layer for further processing.
  • The Transport layer ensures that data is delivered correctly in sequence to the correct destination host by doing error detection, correction (by resending), and reordering of messages.
  • It is responsible for providing end-to-end communication services for applications.
  • It is also responsible for providing reliability by doing flow control and error control.

Application Layer

The Application layer is the fourth layer of the TCP/IP model, and it combines the functionalities of the Session, Presentation, and Application Layers of the OSI model. In addition, it provides the interface between the application and the network.

It is responsible for presenting data to the user. Applications such as Web browsers and FTP/Email clients are used on this layer. Its data unit is the Data, and Application layer protocols are FTP, HTTP, HTTPS, etc.

What are the functions of the Application layer?

  • The Application layer is responsible for the user interfaces and application services.
  • The user interfaces include a command-line, menu-driven, and graphical user interface.
  • The application services include e-mail, file transfer, remote login, and World Wide Web.
  • The Application layer is responsible for formatting messages into a format that the underlying transport layer services can transport. It also ensures that messages are properly received and interpreted by the receiving application.
  • The application layer ensures that the data is delivered to the correct application process.

What are some common protocols associated with each layer of the TCP/IP model? 

The TCP/IP model is a four-layer model that consists of the Application, Transport, Internet, and Network Access layers. 

  • The application layer protocol suite includes HTTP, FTP, SMTP, and DNS. 
  • Standard protocols associated with the Transport layer include TCP and UDP. 
  • The Internet layer has network protocols which include IP, ICMP, and ARP. 
  • Network Access layers have protocols like Ethernet, Wi-Fi, RS232, etc. 
The TCP IP model layers Interaction
The TCP IP model layers Interaction

How does data flow through the layers of the TCP/IP model?  

Similar to the OSI model, in the TCP/IP model, Data flows through the layers in a serial fashion. Each layer takes the data it receives from the layer above it, adds its own headers and trailers (as appropriate), and passes the resulting data down to the next layer.

Let us take an example of a web browser talking to a web server. In this case, data will flow from top to bottom through the layers in the following order: the Application layer, the Transport layer, the Internet layer, and the Network Access layer. Where each layer will encapsulate and decapsulates packets to process data and pass data to the next layer.

On the other side of the application, where the Web server lies, data will follow from bottom to up, following the Network Access Layer, the Internet layer, the Transport layer, and finally reaching the Application layer.

how to use the tcp ip model for troubleshooting
How to use the TCP IP model for Troubleshooting

How can the TCP/IP model be used to troubleshoot networking issues?  

The TCP/IP model can be used to troubleshoot networking issues by identifying the problem at each layer and then resolving it. For example:-

  • If there is a problem with the network interface, you can check the Physical layer for a loose cable or a bad connection.
  • If the problem is with the network layer, you can check the IP address to see if it is valid and routable.
  • If the problem is with the transport layer, you can check the TCP or UDP port to see if it is open.
  • If the problem is with the application layer, you can check the application itself for errors. 

Conclusion

The TCP/IP model has proven to be a robust and flexible architecture that you can use in various network types. Therefore, it is crucial to understand the different layers of the TCP IP model and how they interact with each other to troubleshoot problems and optimize network performance.  We have touched on almost all aspects of the TCP IP model in this article; let me know if you want me to add anything else. 

You can refer to TCP IP RFC 1180 for further study.

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Afroz Ahmad

My name is Afroz. I am a CCIE, and I have been working in Networking Industry for more than 14 years. Currently, I work as a Network Designer for a large Organization. I write about technical topics and challenges a Network engineer faces in day-to-day life in my blog. I love to teach people, and I believe in the simple concept that teaching makes you a better learner.

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