1. INTERNET DATA FLOW Created by David Whitchurch for ISDS 4120 Louisiana State University

2. CONTENTS Overview What is a Web Server? The Hardware – A Big Picture of Internet Devices The TCP/IP Model – A Big Picture of Internet Data Flow Step One: Packing It Up Step Two: The Address Label Step Three: Getting to the Internet Step Four: Hopping Though the Internet Step Five: The Destination Network Step Six: Unpacking the Data Conclusion

3. OVERVIEW: WHAT IS A WEB SERVER? When you access the internet, your ultimate goal is to interact with a web server. The URL of theURL server refers to not only the address of the server on the internet, but also to the location of the file or program you are accessing on the server. For example, http://www.lsu.edu/david/stuff refers to the subfolder, “stuff”, inside of the “david” folder on the lsu web server. In fact, the way that the web server processes and stores data is much like your personal computer.

4. OVERVIEW – THE HARDWARE: A BIG PICTURE OF INTERNET DEVICES MOUSE OVER UNDERLINED TERMS FOR MORE INFORMATION START: Your Web Browser LANRouting Switch Gateway NIC Intermediate Routers (“Hops”)Destination Gateway Destination Router Destination Switch Web Server NIC Web Server

5. OVERVIEW – THE TCP/IP MODEL: A BIG PICTURE OF INTERNET DATA FLOW MOUSE OVER UNDERLINED TERMS FOR MORE INFORMATION Application Layer Transport Layer Internet Layer Network Interface Layer

6. STEP ONE: PACKING IT UP APPLICATION & TRANSPORT LAYERS When you type a URL (e.g., “http://lsu.edu”) into your web browser, TCP makes sure you have a connection to the server you are attempting to contact. It also packages your request and any other data into packets and adds the source and destination port numbers to the packets. Port numbers identify the specific process to which an Internet or other network message is to be forwarded when it arrives at a server (e.g., packets sent to port 80 are handled by the web server or a web browser). Sequence and acknowledgement information is also included.

7. STEP TWO: THE ADDRESS LABEL INTERNET LAYER In this step, the Internet Protocol (IP) adds the numeric destination IP address to the packets. The packets are now ready to be sent out to the local network, through gateways to the internet, and to the destination web server.

8. STEP THREE: GETTING TO THE INTERNET NETWORK INTERFACE LAYER In this step, the data packets are sent out through the computer’s Network Interface Card (NIC) into the local network. From here, they travel through the local router switch to the gateway, which sends the packets into the internet, a web of interconnected networks.

9. STEP FOUR: HOPPING THROUGH THE INTERNET NETWORK INTERFACE LAYER, INTERNET LAYER In this step, the data packets travel through the internet until they reach their final destination – the web server’s network. Each step of the journey from one router to another is considered one hop. If a packet doesn’t reach its destination within a certain number of hops, it is destroyed and will be automatically resent.

10. STEP FIVE: THE DESTINATION NETWORK NETWORK INTERFACE LAYER, INTERNET LAYER When each packet of data reaches the destination network, the network’s switch sends the packet to the web server using the IP address and port information contained in the packet.

11. STEP SIX: UNPACKING THE DATA TRANSPORT LAYER, APPLICATION LAYER Once each data packet arrives at the web server, the data inside the packet is unpacked, reassembled, and translated into the format (HTTP) which the web server reads and acts on. The action may be sending a web page or other file back to you, processing data, and/or storing data in a database.

12. CONCLUSION THE PROCESS REPEATS… The processes that each data packet follow in getting to the web server are repeated to get data back to the original computer. These processes are repeated over and over until the connection is terminated.