The Hindu Business Line : Working of the Internet

The header consists of 11 fields, Source port, Destination port, Sequence Number, Acknowledgement Number, Data offset, Reserved, control Bits (flags), window, Checksum, Urgent pointer, and the last one is optional. SYN, ACK are used in the Control Bits (Flags).

SYN (Synchronise sequence numbers): Synchronises sequencing counters for the connection. This bit is set when a segment requests opening of a connection.

ACK (Acknowledgement): Notification sent from one network device to another to acknowledge that some event occurred (the receipt of a message). This field is significant.

When a system sends some data to the Internet it sends a Synchronisation (SYN flag set) packet to initiate a connection. The SYN packet holds a Sequence Number. This Sequence Number is a 32-bit field in TCP segment header. This sequence number is used to make sure that the data delivered at the other end is in the correct order.

If the other host successfully receives the packet, it replies with an acknowledgment and synchronisation (SYN-ACK). The Acknowledgment Number is a 32-bit field in TCP segment header. The TCP checks that no bytes are damaged by using a checksum.

ACD: Automatic Call Distributor

It is a device that distributes incoming calls to a specific group of terminals. It is part of a computer telephony integration system. This device can be used at a call centre that routes incoming calls to targets within that call centre. When an incoming call is received, the ACD system coordinates with the Interactive Voice Recognition system to determine the customer's selection i.e., the menu option he selected. The ACD system then looks into the databases to retrieve the customers' account or other relevant information and transfers the call through the PBX (Private Branch Exchange) to a qualified customer service representative.

If you want to know more details about TCP packets and ACD, please check this site: http://en.wikipedia.org/wiki/Main_Page

How the Internet works:

With the Internet, we are able to see the data we request in a matter of seconds. But many big processes are initiated in the background for this magic to happen.

When you type the Web address in Internet Explorer, the first thing your computer does is look up the exact address of that destination — called an IP address (IP stands for Internet Protocol). To get this IP address, your computer sends a request to a Domain Name Server (or DNS). It's basically a computer program whose sole job is to convert common every-day Internet domain names into their numeric IP equivalent. Armed with this IP address, your computer now knows where to send the data.

Then it breaks up the data into a whole lot of same-sized pieces (called packets).

A header is added to each packet that explains where it came from, where it should end up and how it fits in with the rest of the packets.

Then your computer starts sending each packet to its destination through the gateway server (Router) which is connected to the Internet, then each computer along the way decides where next to send the packet. The packets may not all take the same route.

At the destination, the packets are examined. If there are any packets missing or damaged, a message is sent asking for those packets to be resent. This continues until all the packets have been received intact.

The packets are reassembled into their original form.

Each computer connected to the Internet has software called TCP/IP (Transmission Control Protocol/Internet Protocol), which is responsible for receiving, sending and checking packets. This whole process usually takes a fraction of a second.

Solution by Bharath Kumar V

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