4-TCP_IP_Tutorial
TCP/IP Tutorial
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Introduction to TCP/IP
TCP/IP stands for Transmission Control Protocol / Internet Protocol.
The standard defines how electronic devices (like computers) should be connected to the Internet, and how data should be transmitted between them.
TCP/IP is the Internet Communication Protocol. A communication protocol is a description of the rules computers must follow to communicate with each other.
Internet browsers and Internet servers use TCP/IP to connect to the Internet. Your browser uses TCP/IP to access Internet servers, and servers use TCP/IP to send HTML back to your browser.
Your e-mail program uses TCP/IP to connect to the Internet for sending and receiving e-mails.
Your Internet address "210.75.224.41" is a part of the standard TCP/IP protocol. (And so is your domain name "www.someonesplace.com")
Inside TCP/IP
Hiding inside the TCP/IP standard there are a number of 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
TCP is for communication between applications.
When an application wants to communicate with another application 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 setup 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 is simpler and less reliable.
IP
IP is Connection-Less
IP is for communication between computers.
IP is a "connection-less" communication protocol. It does not occupy the communication line between two communicating computers. This way 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 its 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 its 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.
TCP and 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 receiver.
TCP/IP Addressing
IP Addresses
12 digit numbers are hard to remember. Using a name is easier.
All over the world, a large number of DNS servers are connected to the Internet. DNS servers are responsible for translating domain names into TCP/IP addresses and update each other with new domain names.
TCP/IP Protocols
TCP/IP is a large collection of different communication protocols based upon the two original protocols TCP and IP.
TCP - Transmission Control Protocol
TCP is used for transmission of data from an application to the network.
TCP is responsible for breaking data down into IP packets before they are sent, and for assembling the packets when they arrive.
IP - Internet Protocol
IP takes care of the communication with other computers.
IP is responsible for the sending and receiving data packets over the Internet.
HTTP - Hyper Text Transfer Protocol
HTTP takes care of the communication between a web server and a web browser.
HTTP is used for sending requests from a web client (a browser) to a web server, returning web content (web pages) from the server back to the client.
HTTPS - Secure HTTP
HTTPS takes care of secure communication between a web server and a web browser.
HTTPS typically handles credit card transactions and other sensitive data.
SSL - Secure Sockets Layer
The SSL protocol is used for encryption of data for secure data transmission.
SMTP - Simple Mail Transfer Protocol
SMTP is used for transmission of e-mails.
MIME - Multi-purpose Internet Mail Extensions
The MIME protocol lets SMTP transmit multimedia files including voice, audio, and binary data across TCP/IP networks.
IMAP - Internet Message Access Protocol
IMAP is used for storing and retrieving e-mails.
POP - Post Office Protocol
POP is used for downloading e-mails from an e-mail server to a personal computer.
FTP - File Transfer Protocol
FTP takes care of transmission of files between computers.
NTP - Network Time Protocol
NTP is used to synchronize the time (the clock) between computers.
DHCP - Dynamic Host Configuration Protocol
DHCP is used for allocation of dynamic IP addresses to computers in a network.
SNMP - Simple Network Management Protocol
SNMP is used for administration of computer networks.
LDAP - Lightweight Directory Access Protocol
LDAP is used for collecting information about users and e-mail addresses from the internet.
ICMP - Internet Control Message Protocol
ICMP takes care of error handling in the network.
ARP - Address Resolution Protocol
ARP is used by IP to find the hardware address of a computer network card based on the IP address.
RARP - Reverse Address Resolution Protocol
RARP is used by IP to find the IP address based on the hardware address of a computer network card.
BOOTP - Boot Protocol
BOOTP is used for booting (starting) computers from the network.
PPTP - Point to Point Tunneling Protocol
PPTP is used for setting up a connection (tunnel) between private networks.
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 see 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.