every 15 days to exchange lessons

TCP/IP Tutorial:

Your Browser and Server use TCP/IP:

Browsers and servers use TCP/IP to connect to the Internet.

A browser uses TCP/IP to access a server. A server uses TCP/IP to send HTML back to a browser.

Your E-Mail uses TCP/IP:

Your e-mail program uses TCP/IP to connect to the Internet for sending and receiving e-mails.

Your Internet Address is TCP/IP:

Your Internet address "41.97.143.248" is a part of the standard TCP/IP protocol (and so is your domain name). 

TCP/IP Introduction:

TCP/IP is the communication protocol for the Internet.

Computer Communication 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:

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: 192.68.20.50
This might be the same IP address:  www.w3schools.com

An IP Address Contains 4 Numbers:

Each computer must have a unique IP address.

This is your IP address: 41.97.143.248

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: 192.168.1.50.

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.

w3schools.com is a domain name.

When you address a web site, like http://www.w3schools.com, 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.

TCP/IP Email:

Email is one of the most important uses of TCP/IP.

You Don't :

When you write an email, you don't use TCP/IP.

When you write an email, you use an email program like Lotus Notes, Microsoft Outlook or Netscape Communicator.

Your Email Program Does:

Your email program uses different TCP/IP protocols:

• It sends your emails using SMTP
• It can download your emails from an email server using POP
• It can connect to an email server using IMAP

SMTP - Simple Mail Transfer Protocol:

The SMTP protocol is used for the transmission of e-mails. SMTP takes care of sending your email to another computer.

Normally your email is sent to an email server (SMTP server), and then to another server or servers, and finally to its destination.

SMTP can only transmit pure text. It cannot transmit binary data like pictures, sounds or movies.

SMTP uses the MIME protocol to send binary data across TCP/IP networks. The MIME protocol converts binary data to pure text.

POP - Post Office Protocol:

The POP protocol is used by email programs (like Microsoft Outlook) to retrieve emails from an email server.

If your email program uses POP, all your emails are downloaded to your email program (also called email client), each time it connects to your email server.

IMAP - Internet Message Access Protocol:

The IMAP protocol is used by email programs (like Microsoft Outlook) just like the POP protocol.

The main difference between the IMAP protocol and the POP protocol is that the IMAP protocol will not automatically download all your emails each time your email program connects to your email server.

The IMAP protocol allows you to look through your email messages at the email server before you download them. With IMAP you can choose to download your messages or just delete them. This way IMAP is perfect if you need to connect to your email server from different locations, but only want to download your messages when you are back in your office.