TCP/IP stands for Transmission Control Protocol/Internet Protocol.

TCP/IP is the descriptive framework for internet protocol suit of computer network protocol. This is developed by the united states department of defence (DoD), also called DoD model. TCP/IP is the concise version of OSI model.

DARPA: DARPA is an agencies of united states Department of defence created in 1970.

TCP/IP has four layers:

1. Application layer: 

Application layer is performs the functions of top three layers of OSI model: Application, Presentation and Session layers. This is creates the data files and emails, providing an interface for the user to interact with application and sevices. Creates the session, synchronization, encryption-decryption, encoding-decoding.

protocols of application layer:

FTP-21, HTTP-80, HTTPS-443, SMTP-25, TELNET-23, DNS-53, SSH-22, NTP-123 ect.

2. Transport (Host-to-Host) Layer: 

This layer is responsible for end-to-end delivery of data. Data segmention occurs at this layer and adds the port number (source port and destination port). 

TCP (Protocol no.-6) and UDP(Protocol no.- 17) works on transport layer. The PDU of the transport layer is segmention of the data. Segmentation of the data means small chunks of the data.

3. Internet (Network):

This layer provides the same function of osi's Network layer. Provides the logical address and path detemination(Routing). At this layer adds the source ip and destination ip. 

The main protocols are residing at the Network layer are:

IP, ICMP & ARP

4. Network access:

This layer is combination of Data link and Physical layer of OSI model. At this layer adds the frame and converts into the bits.