TCP/IP Model


 It was developed prior to the OSI model and this model is not exactly similar to the OSI model. It was designed by the Department of Defence(DOD)

It consists of four layers & which is mentioned below

  • Application layer
    • Transport Layer
    • Internet layer
    • Network Access Layer

 1. Network Access layer– It is the lowest layer of this TCP/IP model and It is the combination of physical and data link layer of OSI model. Network Access layer is mainly responsible for transmission of data between two devices on the same network.

Layer one of this model are encapsulating the IP header or IP datagram into frame transmitted by the network and mapping of IP address into physical addresses.

Protocol used on this layer are Ethernet, token ring, frame relay, ATM. etc.

This layer defines how the data should be sent physically through the network,

2. Internet layer

It is a second layer of TCP/IP Model and also famous as network layer. The main task of this layer is to send the packets from any network and they reach one’s destination irrespective of the route they take.

now you can learn CCNA Online, for more information visit

List of the protocol used on this layer are:

  1. ARP It stands for Address Resolution Protocol and it translate IP address to physical address (MAC Address). ARP request and ARP reply are two term associated with this protocol and when a sender wants to know the physical address of the device it will broadcast the ARP request on the network. And the devices connected to the network will accept the ARP request & they will process the request, but only recipient device detect the IP address and sends back its physical address in the form of ARP reply. The recipient device adds the physical address both to its cache memory and to the datagram header.
  • IP- Internet protocol is used in this layer & it is the most significant part of the TCP/IP Protocol Suite. IP Address is used by the internet and higher layers to identify or detect the device and to provide internetwork routing. It determines the path through which data is to be transmitted.
  • ICMP- It stands for Internet Control Message Protocol. It is a process used by the hosts or routers to send notifications regarding datagram problems back to the sender. the main responsibility of this protocol is to report the problems and not to correct them. The responsibility of the correction lies with the sender. It can send the messages only to the source, but not to the intermediate routers because the IP header or IP datagram carries the addresses of the source and destination but not of the router that it is passed to

3. Transport layer– It is mainly responsible for the reliability, flow control, and correction of data which is being sent over the network. Protocol used on this layers are mentioned below

a) UDP (User Datagram Protocol)

  • It is a connectionless protocol.
  • It is an unreliable protocol.

UDP Header fields are mentioned below:

a) Source port address: It is the address of the application program that has created the message.

b) Destination port address: It is the address of the application program that receives the message.

c) Total length: It defines the total number of bytes of the user datagram in bytes.

d) Checksum: It is a 16-bit field used in error detection.

This protocol does not specify which packet is lost. It contains only checksum; it does not contain any ID of a data segment. example of this protocol will be VoIP, Video Streaming, Live Streaming, YouTube Video.

TCP – It is a connection oriented protocol and an internet protocol suite which breaks up the message into TCP Segments and reassembling them at the receiving side. It is reliable protocol and follow sequencing method. example of this will be download, file sharing printing

Online CCNA Training with interactive session available at

4. Application Layer

It is the top layer of TCP/IP protocol Suite and allows the user to interact with the application. This layer is responsible to handle high end protocols like http, SNMP, SMTP, DNS, TELNET, FTP

Application Layer protocols are mentioned below:

a) HTTP – It stands for Hypertext transfer protocol and allows us to access the data over the world wide web. It transfers the data in the form of plain text, audio and video. Port no.

b) SNMP: It stands for Simple Network Management Protocol and It is a framework used for managing the devices on the internet by using the TCP/IP protocol suite.

c) SMTP: It stands for Simple mail transfer protocol. The TCP/IP protocol that supports the e-mail is known as a Simple mail transfer protocol. This protocol is mainly used to send the data to another destination e-mail address. Port no 25

d) DNS: It stands for Domain Name System. An IP address is used to identify or detect the connection of a host to the internet uniquely. But, people prefer to use the names instead of addresses. So, the system that maps the name to the address is known as Domain Name System.

e) TELNET: Telnet is an abbreviation for Terminal Network. Mainly telnet establishes the connection between the local devices(Computer) and remote devices(Computer) in such a way that the local terminal appears to be a terminal at the remote system.

f) FTP: It stands for File Transfer Protocol. FTP is an internet protocol used for transmitting the files from one computer to another computer.

Gyani Labs