Wednesday, 28 April 2021

TCP/IP Model: Layers & Protocol

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The OSI Model we just looked at is just a reference/logical model. It was designed to describe the functions of the communication system by dividing the communication procedure into smaller and simpler components. But when we talk about the TCP/IP model, it was designed and developed by Department of Defense (DoD) in 1960s and is based on standard protocols. It stands for Transmission Control Protocol/Internet Protocol. The TCP/IP model is a concise version of the OSI model.

Before start we need to know what actually is a protocol. In terms of networking, a protocol corresponds to a set of rules which govern how system communicate with each other. Then we need to know what a Protocol suite is. A protocol suite is simply a collection of protocols that are designed to work together.

What is TCP/IP Model?

The TCP/IP (Transmission Control Protocol / Internet Protocol) was created in the 1970s by DARPA. The model came from ARPANET and is also known as the “Internet Model”. TCP/IP model allows us to connect among heterogeneous systems and holds a popular set of communication protocols.It contains four layers, unlike seven layers in the OSI model. The layers are:
Layer 4. Process/Application Layer
Layer 3. Host-to-Host/Transport Layer
Layer 2. Internet Layer
Layer 1. Network Access/Link Layer

How TCP/IP works?

TCP/IP has four abstraction layer which describe a general set of design guidelines and implementations of specific protocols for network communication. We will be discussing all these four layers in brief with some popular protocols of each layer.

4. Application Layer

This layer provides applications the ability to access the services of the other layers and defines the protocols that applications use to exchange data. This layer adds it’s own header and sends down to the Transport layer.

Some of the popular protocols of this layer are: HTTP, FTP, SMTP, Telnet, NFS, RIP, etc.

3. Transport Layer

It is mainly responsible for providing the application layer with session and datagram communication services. It accepts data from application layer, splits it up into smaller units and pass these to the network layer. This layer adds it’s own headers and sends down to the Internet layer. It is the responsibility of this layer to ensure that all the split pieces arrive correctly at the other end. It is concerned with end-to-end transportation of data and setups up a logical connection between the hosts.

There are two protocols available in this layer: TCP and UDP

2. Internet Layer

The segments sent by the above layers are received here. Now, we need to send this segment of data to a destination host which could be anywhere ( in the same network or may be external network). This layer ensures that the segment is moved across the networks to the destination network. It provides logical addressing, path determination for the segments to be sent and forwarding. This layer also adds it’s own headers and convert and send the received segments in form of packets.

Some of the popular protocols of this layer are: Internet Protocol (IP), ICMP, etc.

1. Network Access Layer ( Data Link + Physical Layer)

This layer defines the protocols and hardware required to connect a host to a physical network and to deliver data across it. For delivery within a given physical network, packets are sent from the above layer to this layer. The destination can be another host in the network, itself, or a router for further forwarding. So the Internet layer has a view of the entire Internetwork whereas the Network Access layer is limited to the physical layer boundary that is often defined by a layer 3 device such as a router.

The protocols in this layer depends upon which physical network is being used. When the physical network is LAN, Ethernet (802.3) and it’s many variants are used while if the physical network is a WAN, protocols such as Point to Point Protocol (PPP) and Frame relay are common.

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