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TCP/IP Introduction

TCP/IP Introduction

TCP/IP is the communication protocol for the Internet.

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

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.

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


  • 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.

  • 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.

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.

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.


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.




TCP/IP Addressing

TCP/IP uses 32 bits, or four numbers between 0 and 255, to address a computer.

IP Addresses

Each computer must have an IP address before it can connect to the Internet.

Each IP packet must have an address before it can be sent to another computer.

This is an IP address:
This might be the same IP address:

An IP Address Contains 4 Numbers.

Each computer must have a unique IP address.

This is your IP address:

TCP/IP uses four numbers to address a computer. The numbers are always between 0 and 255.

IP addresses are normally written as four numbers separated by a period, like this:

32 Bits = 4 Bytes

TCP/IP uses 32 bits addressing. One computer byte is 8 bits. So TCP/IP uses 4 computer bytes.

A computer byte can contain 256 different values:

00000000, 00000001, 00000010, 00000011, 00000100, 00000101, 00000110, 00000111, 00001000 …….and all the way up to 11111111.

Now you know why a TCP/IP address is four numbers between 0 and 255.

Domain Names

A name is much easier to remember than a 12 digit number.

Names used for TCP/IP addresses are called domain names. is a domain name.

When you address a web site, like, the name is translated to a number by a Domain Name Server (DNS).

All over the world, DNS servers are connected to the Internet. DNS servers are responsible for translating domain names into TCP/IP addresses.

When a new domain name is registered together with a TCP/IP address, DNS servers all over the world are updated with this information.

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