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How does the Internet work?
Introduction
The Internet (also known as the Net) uses computers, modems and telecommunication links to connect the largest network ofcomputers in the world. It allows millions of computers around the world to link with one another to share information and forpeople to communicate electronically with each other. Each computer has a unique address so then the computers can link toeach other. People can also send each other messages by using Electronic-mail.
How does the Internet work?
Messages are sent from one computer to another. The message can go to the ISP down the phone line via the modem.For the message to go over the Internet, it needs to be translated into electronic signals from alphabetic text.This is done by using TCP/IP protocol stack. It is most often built into the operating system. The stack is madeup of layers. <See Fig. 1>
Fig.1
What are these layers?
These layers are shown in fig. 1. The packets at the TCP layer are assigned a port number. This is done so we know which program on the destination computer needs to receive the message as it will be listening on a specific port. At the IP layer, the packet is given its destination IP address. When the packets arrive at the hardware layer, the text is turned into electronic signals and is transmitted down the phone line. The packets may go off to an ISP and when the packets arrive at the receiving computer, the IP address and port number are moved, and it is turned back into text.
A unique address?
IP addresses are in the form of nnn.nnn.nnn.nnn, where nnn must be a number between 0-255.This is the IP (InternetProtocol version four) address. This address means that information can be send from one computer to another over the Internet. Theaddress is of the size of 32 bits. The first part of the address identifies the network on which the host resides. This is the networkprefix. The second part identifies the particular host on the given network and this is the host number. There are problems with this version of IP addresses.
What are the problems with Ipv4?
The biggest problem with IPv4 is the limited address space. This means that the growth of the Internet and communication devices isrestricted. As all the addresses on the Internet are unique, there can not be any duplicates. Private addresses can be used for networksbut not on the Internet as they are not unique. NAT (Network Address Translation) can be used to link the private addresses tothe Internet. For the duration of the communication on the Internet, a globally unique address is loaned. However, this does mean thedata is altered between its source and its destination. This leads to a security problem.
What is being done about this problem?
IPv6 is a replacement for IPv4 and IPv6 is 128 bits. With IPv6, a new type of address is defined so then it allows nodes to controlthe path the traffic flows. Header format simplification has been done so this means that the header on IPv6 is only twice as long asIPv4. The header, unlike for v4, is at a fixed length of 40 bytes. There is more efficient forwarding and security has been improved.Packets can now be labeled to say which particular traffic flow it belongs to.
How does email work?
An email can be received in seconds after it is sent. The mail client, such as Outlook, opens a connection to its default mail server. The mail server's domain name or IP address is usually set up when Outlook, etc, is installed. The mail server will always transmit the first message to identify itself. The client will send SMTP (Simple Mail Transfer Protocol) HALO command to which the server will respond with a 250 OK message. Depending on what the email program is doing (checking/receiving mail), the appropriate SMTP commandswill be sent to the server, which will respond consequently. The request and response commands will go on until the client send an SMTP QUIT command. The server will then acknowledge the QUIT command and the connection will end.
This is only meant as a rough outline. For further details about:
IPv6 see http://www.ipv6forum.com
Broadband and networking see http://www.broadbandnetworks.info