TCP/IP Model

Like the OSI network model we have also another Network model named TCP/IP model. The TCP/IP model is different from OSI model. OSI have seven layers standard, however TCP/IP has four layers. After taking some layers from OSI, and combine then, developers create a model, which was called TCP/IP. TCP and IP protocols have great importance in network communications that why model have name as TCP/IP. From the below figure we can understand the both model differences.

Comparison chart of Both models:-

OSI Model Layers	TCP/IP Model Layers
Application Layer	Application Layer
Presentation Layer
Session Layer
Transport Layer	Host to Host Layer/Transport Layer
Network Layer	Internet
Data Link Layer	Network Layer
Physical Layer

From the above figure, Application ,Presentation and Session layers are all together as combined called Application layer in TCP/IP Model. Also note that the Network Layer is combination of Data-link Layer and Physical Layer of OSI model. 

Layer 4. Application Layer 

Application layer is the top most upper layer of TCP/IP model. The TCP/IP Application layer protocols operate at the Session, Presentation and Application layers of the OSI model. this layer enables applications to communicate with one another and it provides access to the services of the underlying layers.There is a wide variety of Application layer protocols, all of which rely on all the TCP/IP services beneath them in the protocol stack. This layer is responsible for TCP/IP application protocols and any host or computer programs interface with layer 3 services to use the network.

Application layer includes all the higher-level protocols like DNS, HTTP, Telnet, FTP, SNMP, SMTP, DHCP, RDP etc

Layer 3. Transport Layer

The layer 3 of TCP/IP model is Transport layer sometimes its called host to host protocol also. Transport layer is responsible for data conversion at time of transferring, the working protocol on this layer divided the data in segments, after labeling them, reassembling,  flow control, error connection, and when reach data on other hand, again arrange data in the sequence in that the real data received. 

The main protocols of Transport layer are TCP and UDP.  

Layer 2. Internet Layer 

The second layer 2 of the  TCP/IP model Internet Layer. The position of Internet layer is between Network Access Layer and Transport Layer. Internet layer is responsible to pack data into data packets known as IP data-grams, which contain source and destination addresses. These information is used to forward the data-grams to the hosts or across networks. The routing of IP data-gram is one of the work of this Internet layer.

The main protocol of Internet layer are IPv4, IPv6, ICMP, IGMP, IGRP, IPX, Apple talk DDP, EIGRP etc.

 Layer 1. Network Access Layer 

This is the first layer of the four layer TCP/IP model. This layer 1 is responsible ,how data would be physically sent through the network, including how bits are electrically or optically signaled by hardware devices that interface directly with a network medium, such as coaxial cable, optical fiber, or twisted pair copper wire. 

Ethernet, frame relay, DTP, CDP, L2F, SLIP, STP, etc are some protocols that’s working on this layer.

But most common model which is using in Modern time is OSI model. 

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