Skinny’s Trip Over the Internet

This is an article for children.

            Larry Baltimore is a sixth grader careful about spelling and grammar. He types his email message on the word processor and runs it through spelling- and grammar-checks. Then he cuts the message and pastes it in his email ‘Compose’ folder.

            When Larry opens the word processor, the office assistant comes in from the right hand corner of the computer as a scooter followed by a sort of a striped yellow mat. Then he hops and becomes a sort of a paper clip with long black eyelashes. He blinks from time to time, watching Larry with his large eyes.

            Larry nicknames it Skinny. When Larry closes the word page, Skinny hops into a scooter again and zooms away into the computer.

            One day Skinny decided to see where Larry sent his message. Little did he know that he was in for an adventure. When Larry cut his message to his friend Bart Weatherly, and pasted it in his email compose folder and closed the word processor, Skinny hopped into the computer as usual. Then he infiltrated the email zone.

            Larry clicked ‘Send’ and Skinny and the message arrived at the first of the four layers of the computer used for sending email. “Hi, I’m the Application layer,” the first layer announced. “Who are you, stranger?”

            “I’m a friend of Larry,” Skinny said. “I’m curious about how his message travels over the Internet.”

            “You’re welcome,” the Application layer said. “My job is to send the message to the second layer. Normally only email messages are allowed here but I’ll let you go by since you’re hungry for knowledge.” The application layer then forwarded Larry’s message and Skinny to the next layer, the Transmission control protocol, or TCP, layer.

            Protocol is the name for the language that computers use to talk to each other over the Internet.

            “Stranger, what are you doing here?” the TCP layer growled at Skinny.

            “I’m a word assistant. I want to see where Larry sends his message.”

            “Fair enough,” the TCP layer said. “My duty is to dispatch the message to the third layer. But messages arriving here are often too large to travel over the Internet. So I break them down into small pieces called packets. I must reduce you into a packet too.”

            Skinny jumped back, shivering.

             “You don’t have to worry,” the TCP layer said with a smile. “You’ll come out alright at the end.”

            “Okay then,” Skinny said and the TCP layer chopped him and Larry’s message into bits.

            Am I really cut into pieces?  Skinny asked himself as he still felt whole.

            Each computer connected to the Internet has an address known as Internet Protocol, or IP, address. Larry’s Computer’s is 156.21.10.66 and Bart’s is 221.5.358.17.

            After reducing Skinny and Larry’s message into chunks, Skinny’s head was put into one of the packets. Skinny saw the TCP layer add Larry’s computer’s address and the number 25 to the packets. This number is called a “port number” and helps identify the packets as email. The TCP layer then sent the packets to the third layer, the IP layer.

            Skinny peeped out of the packet and saw the IP layer label each of the packets with Bart’s computer’s address and then sent them to the last layer, the hardware layer.

            To be able to continue the journey over telephone lines, the electronic language of the computer must be turned into telephone language. A machine called a modem at the hardware layer does this. Skinny felt a beep and then the packets left Larry’s computer and headed for Bart’s.

            Skinny’s eyes widened when the packets arrived at Internet machines called routers, “Wow,” he said, “the information superhighway.”

            The routers are connected to each other, forming a complex system similar to a network of roads and bridges and the packets hop through them to their destination.

Skinny saw all sorts of packets jumping from one router-highway to another on their way to computers all over the world.

            When the email packets arrived at the first router, it examined the destination address they carried.

             “221.5.358.17 doesn’t belong to our network,” it said and sent the packets to the next router which might know where to send them.

            The next router did the same.

             This continued until the packets came to the router which recognized Bart’s address. Then it sent them to a transit stop in another machine called a web server. A server receives packets and stores them until they are picked up.

            Each server has a name. The last part of an email address following the @ is the server address. Bart’s server address is usa.com and his username is bartweatherly. Once the packets reached the usa.com server, they were channelled into the account bartweatherly@usa.com.

            When Bart logged in to check his box for mail, the request went to the usa.com server. The server checked the usernames placed on it, found bartweatherly@usa.com and then sent the packets through the telephone line to the hardware layer of Bart’s computer.

            For the computer to receive the message, the modem converted the telephone language into electronic language and then sent the packets to the IP layer.

            Skinny watched the IP layer take off the destination address 221.5.358.17 from the packets and push them to the TCP layer. The TCP layer in turn took off the packets

Larry’s computer’s address 156.21.10.6 and the port number 25. Then it reassembled the packets into the original message sent by Larry and into Skinny. Skinny examined himself and he was whole. He and the message were then pushed to the application layer where Bart read the message.

            “So this is what happens between the time Larry sends his message and when his correspondent reads it,” Skinny said to himself, nodding.

            When Bart Leopold wrote his reply directly in the email compose folder and clicked ‘Send,’ the process was repeated.

            Larry, as usual, read Bart’s message and then went to the word processor to write his answer.

            Skinny zoomed from the email application layer to the word processor and blinked at Larry, scratching his head. But Larry continued to work. How Skinny wished he had a way of letting Larry click on him to ask what happens to his email message between the time he clicks ‘Send’ and when the mail reaches its destination! He was sure Larry would be surprised to learn all the changes that happened before his message reached Bart.