What are the functions of each layer in TCP/IP?

Transmission Control Protocol/Internet Protocol (TCP/IP) are two different communication protocols. TCP splits a message to packets which were transmitted across the internet whereas the IP is accountable to address of every packet hence a chance to forward the exact destination.

Previously, there was no TCP/IP and no method for the computers to perform effortlessly over public networks. The main function of TCP/IP is that it governs how the information is sent and received in the form of packets between source and destination.

So in short, we can say that TCP defines the communication in a network and how to send data in the form of packets. IP manages how to make the route for packets to make sure it reaches its defined destination. Before the data is sent its IP address is checked then it is determined where to forward the data.

TCP/IP uses the same model as the Open Systems Interconnection (OSI) model. It uses the client/server model type of communication where a user or machine (a client) is provided a service by another computer (a server) in the network.

Layers of TCP/IP

TCP/IP has four layers which are as follows −

  • Application Layer
  • Transport Layer
  • Internet layer
  • Network access layer

Let us learn about each of the four layers.

Application layer

It is a Top most layer which is equivalent to Application, Presentation and Session layer of OSI model.

It acts as an interface between the application programs and has the same capable features of Application, Presentation and Session layer of OSI model.

It uses protocols like SMTP, HTTP, HTTPS, FTP, NTP, SSH, Telnet SNMP etc all work on this layer.

In this layer, data acts as a Protocol Data Unit (PDU).

Host-to-Host layer

It is equivalent to the transport layer of the OSI model and is responsible for delivery of data.

It depends on which type of protocol is used whether it’s Transmission Control Protocol (TCP) or User Datagram Protocol (UDP).

If reliable delivery of data is needed, then TCP will be used. UDP is used, if fast delivery without reliability is needed.

In this layer, TCP and UDP the protocols which are used and data acts as a Protocol Data Unit (PDU).

Internet layer

It is equivalent to the Network layer of the OSI model. Logical addressing and routing is performed at this layer by using the IP address of a device.

At this layer the routers forward the packet on the basis of IP addresses of devices. IP is the most important protocol at this layer

The protocols used at this layer are Internet Control Message Protocol (ICMP) and Internet Group Management Protocol (IGMP).

PDU at this layer is Packet.

Network Access layer

It is equivalent to the Data link layer and Physical layer of the OSI model. Hardware addressing is done at this layer.

It defines protocols for physical transmission of data. Ethernet is the most important protocol used at this layer.

Fast Ethernet, Token Ring and Fiber Distributed Data Interface (FDDI) are other protocols at this layer.

PDU at this layer is called frame.