How Data Flows through the Internet Lindsay Haley

What happens when… http://www.yourcompany.com So what happens in the milliseconds after you enter a website address and a webpage is loaded onto your screen? How does information get from your computer to its destination and back?

Data Flow www.yourcompany.com = 172.22.30.47 Web Address IP Address Google.com 74.125.224.72 Yourcompany.com 172.22.30.47 ...... …… What is www.yourcompany.com’s IP Address? DHCP Server Most people nowadays have routers or hubs that allow multiple computers (or devices) to share the same connection to your Internet Service Provider (ISP), in your case it’s Cox Communications. For the purposes of my explanation, I did not include a graphic for a router on the slide. Routers are used to convert electrical pulse signals from your copper cable line into a signal your computer’s wireless card can read (radio waves). They are also used to forward information to a specific device connected to your network, via an IP address. When you first turn your computer on, it will send out a request to have an IP address for your home network. This is not a unique address world-wide, but it is unique to your home network. After you type a website address and hit enter, your computer sends that information to the DHCP (Dynamic Host Control Protocol) Server, which has a list of the web address conversion from text to IP addresses. IP addresses are more easily readable by computers than strings of words in a web address. We, as humans, use names and words for the URL because it’s easier for us to remember them. Your Computer www.yourcompany.com = 172.22.30.47

Home ISP Data Flow The Internet yourcompany ISP yourcompany Server Once your computer locates the IP address of the website, it will send a request to view yourcompany.com’s website to Cox. Cox will then connect you to the Internet, which is represented by a cloud because we do not know precisely how everything is connected or how your information is routed once you go beyond your ISP. After the request has gone through “the cloud”, it will be connected to yourcompany’s ISP, and finally it will reach yourcompany’s server. The Internet yourcompany ISP

Home ISP Data Flow The Internet yourcompany ISP yourcompany Server Once your request is accepted by yourcompany’s server, it will forward the requested information back to your computer. This process may not follow the exact route that it initially took to return the data to your computer. (continued on next slide) The Internet yourcompany ISP

Data Flow www.yourcompany.com = 172.22.30.47 Web Address IP Address Google.com 74.125.224.72 Yourcompany.com 172.22.30.47 ...... …… What is www.yourcompany.com’s IP Address? DHCP Server (continuation of previous slide) Your Computer www.yourcompany.com = 172.22.30.47

YourCompany.com http://www.yourcompany.com And now, your webpage has loaded onto your home computer screen.

Now to the more technical stuff… Overview thus far: Thus far, we’ve seen how your computer uses IP addresses to request information from the DHCP server, and use that information to reach your destination website. Now, we’ll discuss some more technical aspects of the data flow process.

The OSI Model (the image presented on the slide shows the layers in descending order) The OSI (Operation Systems Interconnection) Model is used to show how data travels through one device to another through the network. Layer 1, Physical: The physical layer is comprised of physical links between devices, such as the cabling that connects the devices. In our example from before, this would be your computer connected to your router, and your router connected by Ethernet cable to your cable modem to Cox. Layer 2, Data Link: This layer identifies the devices on the physical layer. Also, the data being sent is composed to small pieces called packets. The sending computer chops the data into packets and gives them a number so that the receiving computer knows how many pieces were supposed to arrive and which ones (if any) were lost along the way. The receiving computer can request the specific packets it’s missing instead of asking for all of them again. This would be your computer checking to make sure that it can connect to the internet and it’s forming your request to view yourcompany.com website into packets. Layer 3, Network: Determines how the data will be sent to the recipient. Like a map, this will determine how the data will arrive at it’s destination. If there are any roadblocks, it will know that there are other ways it can take to reach the end. Layer 4, Transport: Ensures that the data is transferred completely and correctly from the sender to the recipient. This is where your computer is sending the request to view the webpage. Layer 5, Session: Establishes and maintains a connection between the sending and receiving devices while the data is being sent. This is when you are connected to the yourcompany.com and are receiving data from their website, before it is displayed onto your computer screen. Layer 6, Presentation: Converts the data into a form that the recipient can view and sorts the packets back into sequential order. This is done in the background of your computer before the webpage is displayed onto your screen. Layer 7, Application: Interacts with your computer’s OS (operating system: Windows, Mac Osx, etc.) to allow the user to view the data. This would occur when the webpage loads on your screen and you may begin to interact with the webpage.

TCP/IP TCP/IP Protocol HTTP TCP ports (the image presented on the slide shows the layers in descending order) There is also the TCP/IP (Transmission Control Protocol)/(Internet Protocol) Protocol which is a more loosely defined protocol that is similar to the OSI model. Layer 1, Network Interface: combines the physical and data link layers of the OSI model. It routes the data between devices on a network and manages the exchange of data between the network and devices outside of the network Layer 2, Internet: corresponds to the network layer of the OSI model. Uses IP addresses to identify both the sender and the receiver Layer 3, Transport: asks the recipient device if it is willing to accept the information from the sending device Layer 4, Application: combines the session, presentation, and application layers of the OSI model. TCP ports are used to help identify the destination computer. They are added to the IP address of the sending computer to help further ensure that the data is transmitted to the correct destination. Hypertext Transfer Protocol (HTTP) is a protocol used for communication on the web. It allows for users to access content and data on webpages.

Types of Addresses IP address Ethernet Address Example MAC address: 38:4B:2E:A0:9F Here we’re coming back onto a topic I briefly mentioned earlier: IP addressing. IP addresses are assigned either manually or automatically. Manual addressing, for our purposes, is how when a website is registered with the IANA (Internet Assigned Numbers Authority), the website is manually given a static IP address. This means that the IP address will not change until the owner chooses to change it or take down the website. There is a protocol called DHCP (Dynamic Host Configuration Protocol), where the network gives the users an IP address. When you turn on your computer, it will send a request to the network asking for an IP address. The network will give it an IP address and tell it the length of time it can have that address (DHCP Lease). The DHCP Lease is to allow for multiple users to come on and off the network by recycling the IP addresses. Remember: DHCP-assigned IP addresses are unique to your network but not unique around the world. Ethernet Address is another way of saying the physical address or MAC (Media Access Control) address. MAC addresses are totally unique to each device, world-wide for computers, tablets, smartphones, etc. Each manufacturer is given a range of MAC addresses to assign to each NIC (network interface card). MAC addresses are composed of a hexadecimal set of numbers, meaning that the characters included will range from 0-9 and A-F.

Vs. Device Functions Router Switch Work Home Routers are used to convert electrical pulse signals from your copper cable line into a signal your computer’s wireless card can read (radio waves). They are also used to forward information to a specific device connected to your network, via an IP address. Say that you have two computers working on different projects on the internet at the same time. You don’t want the other person’s research webpage to appear on your computer and your information on theirs, you want to have your information given directly to you. So having a specific IP address allows the router to know who to send the information to. When you first turn your computer on, it will send out a request to your network for an IP address. The network will respond with an IP address and a DHCP Lease (discussed on slide 11). In addition to asking for an IP address, your computer will also give the router it’s MAC address as the unique identifier of the “person” who has this particular IP address. Switches work relatively the same. For large networks, like LSU, there is one main router for multiple switches per network. You can still relate this to a smaller scale. For example, a switch (like your router at home) allows for many devices to connect to a network. A routing switch allows for many switches—each containing multiple users—to connect to the network.