TCP/IP Introduction

Computer Communication Protocol

A computer communication protocol is a description of the rules computers must follow to communicate with each other.

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What is TCP/IP?

TCP/IP is the communication protocol for communication between computers on the Internet.
TCP/IP stands for Transmission Control Protocol / Internet Protocol.
TCP/IP defines how electronic devices (like computers) should be connected to the Internet, and how data should be transmitted between them.

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Inside TCP/IP

Inside the TCP/IP standard there are several protocols for handling data communication:

• TCP (Transmission Control Protocol) communication between applications
• UDP (User Datagram Protocol) simple communication between applications
• IP (Internet Protocol) communication between computers
• ICMP (Internet Control Message Protocol) for errors and statistics
• DHCP (Dynamic Host Configuration Protocol) for dynamic addressing

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TCP Uses a Fixed Connection

TCP is for communication between applications.
If one application wants to communicate with another via TCP, it sends a communication request. This request must be sent to an exact address. After a "handshake" between the two applications, TCP will set up a "full-duplex" communication between the two applications.
The "full-duplex" communication will occupy the communication line between the two computers until it is closed by one of the two applications.
UDP is very similar to TCP, but simpler and less reliable.

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IP is Connection-Less

IP is for communication between computers.
IP is a "connection-less" communication protocol.
IP does not occupy the communication line between two computers. IP reduces the need for network lines. Each line can be used for communication between many different computers at the same time.
With IP, messages (or other data) are broken up into small independent "packets" and sent between computers via the Internet.
IP is responsible for "routing" each packet to the correct destination.

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IP Routers

When an IP packet is sent from a computer, it arrives at an IP router.
The IP router is responsible for "routing" the packet to the correct destination, directly or via another router.
The path the packet will follow might be different from other packets of the same communication. The router is responsible for the right addressing, depending on traffic volume, errors in the network, or other parameters.

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Connection-Less Analogy

Communicating via IP is like sending a long letter as a large number of small postcards, each finding its own (often different) way to the receiver.

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TCP/IP

TCP/IP is TCP and IP working together.
TCP takes care of the communication between your application software (i.e. your browser) and your network software.
IP takes care of the communication with other computers.
TCP is responsible for breaking data down into IP packets before they are sent, and for assembling the packets when they arrive.
IP is responsible for sending the packets to the correct destination.