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TCP/IP Model

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The Department of Defense (DOD), a division of the United States government, developed a model that would be used as the

developing basis for their own protocol suite known as the Internet protocol suite. The suite of protocols that when combined create the language of the internet. Transmission Control Protocol (TCP) is responsible for ensuring that a message is divided into packets that Internet Protocol (IP) manages and for reassembling the packets into the complete message at the other end. Each packet has a TCP header that includes sequence numbers, acknowledgement numbers, addresses and other pieces of connection information.

The DOD model consists of four layers namely
Network Interface Layer
Internet Layer
Transport Layer
Application Layer

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Network Interface layer
The primary responsibility of the Network Interface Layer is to define how computer connects to a network and it is used to receive packets and to send packets. The Network Interface Layer is sometimes referred to as the Data-Link layer.

Internet layer
The Internet layer contains the protocols that are responsible for addressing and routing of packets. Its job is to permit hosts to inject packets into any network and have them travel independently to destination. It defines an official packet format and protocol called Internet protocol. This protocol is responsible for determining the source and destination IP address of every packet. It includes several protocols, including
1. Internet protocol
2. Address Resolution Protocol
3. Internet Control Message Protocol
4. Internet Group Message Protocol

Transport layer
It determines whether the sender and the receiver will set up the connection before communicating and how often they will send acknowledgement of that connection to each other. It consists of two protocols
1. Transmission Control Protocol
2. User Datagram Protocol

Application layer
The Application layer is the part of the TCP/IP where requests for data or services are processed and applications at this layer are waiting for requests to process and they are all listening at their respective ports. It contains higher level protocols like
2. FTP