How Information Flows via the Internet By: Lee Farrell

What is the Internet? The Internet is simply a wire that is buried in the ground. This wire may be fiber optic, copper, occasionally beamed to satellites, or through cellular networks. 2 computers connected to this wire can communicate. A server is a computer that is directly connected to the internet. Webpages are files on that servers hard drive.

How does it work? Your home computer is not a server. It is considered a client because it is not connected directly to the internet a.k.a (wire). Computers used at home a.k.a (clients) are connected to the internet (wire) through Internet Service Providers (IPS) such as DSL (AT&T), cable (Cox), Satellite (HughesNet), and cellular (Verizon, AT&T, Sprint, etc…) For example: if you wanted to visit Facebook. The information would travel from your computer to your ISP and then to the Facebook server. This now allows you to look at Facebook’s webpages.

The Internet Data

How does the Information Travel? Information travels via the Internet (wire). Whenever your s, picture, or webpages travel across the Internet; computers break the information into pieces called packets (data packets). Whenever the information ( s, pictures, or webpages) reaches its destination, computers reassemble the packets in their original order to make an , picture, or webpage display as they were sent. Each packet is surrounded by a frame, like a shipping box, that contains pertinent information about the contents of the packet such as sender/destination address. The TCP/IP network protocol uses a port numbering system to assign a number b/w 1 and This allows a pathway that data can flow in and out of. The webpage protocol, called Hypertext Transfer Protocol (HTTP), uses port 80 for internet access. Data Packet

Example: Something we use everyday is . How does it work? So you have a Gmail account for example. Your computer connects to Gmail via your Internet Service Provider (ISP). You compose your message and attempt to send it to an aol.com (Server and ISP) account. Once you click send Gmail.com sends the to aol.com via the Internet (wire). Once the recipient dials into aol.com they will receive the and vice versa. Gmail ISP Google Server Aol.com Server/ISP Aol User

The Fundamentals of Information Flow (OSI Model) The easiest way to describe data flowing across the Internet is to segment it into 7 layers. These layers make a model know as the Open Systems Interconnection model (OSI model). We use layers to show the strategic process and organization of the data flow, as well as, simplify the process. It also provides structure and gives us a better understanding of the function and purpose of devices and services relating to certain layers of the model. The 7 layers of the OSI model: 7. Application layer 6. Presentation Layer 5. Session Layer 4. Transport Layer 3. Network Layer 2. Data Link Layer 1. Physical Layer (DP)

The Layers: Layer 1: The Physical Layer The Physical Layer includes all transmission medium such as cables/wireless signals that move bits of data along the network. It provides a means for data to move. Contains hubs which are connected to multiple devices that basically sends data received from one device/system and sends it to all other systems attached. Includes all physical cabling such as fiber optic, copper, etc.. Layer 2: The Data Link Layer Computers are connected to the network via the data link layer. All computers contain a piece of equipment called network interface cards (NIC cards) These NIC cards work on the physical and data link layers to connect to the network. Your computer is connected to the network, for example, via Ethernet which is plugged into your computers NIC card and into the wall via the physical layer ( Ethernet). The client machine builds a data packet to send to the switch/router for processing. Each NIC card contains a unique identifier known as a Media Access Control (MAC address) which is like your home address. No 2 MAC addresses can be the same. These MAC addresses identify your computer on the network. Every computer requires a NIC card to connect to the network. Ethernet(Physical Layer) Switch (Data Link Layer)

Routers and Switches Routers: Anywhere 2 or more parts of the Internet intersect, there is a piece of equipment called a Router. Routers direct your incoming/outgoing packets around the Internet based on destination information (IP address/TCP address) Routers help each packet get closer to its destination. Typically multiple routers, called subnets, will help your packets get to and from its destination each time you visit a webpage. Chop large networks into smaller ones Connects a local network to the internet Routers remove previous network frames from packets and adds a new one for sending that has a new IP and MAC address. Router the sends data to customers ISP which may pass through subnets onto the final IP destination at the web server. Upon receipt the webserver returns website info back to client (As shown on next slide). Switches: used to connect devices together on a computer network. A switch will only send a message to only to the device that request it, unlike hubs that broadcast the message to all devices connected. Most routers today come equipped with a network switch. Processes and forwards data at the data link layer.

The Layers Layer 3: The Network Layer All data transferred via the network travels in packets (data packets) The network layer is responsible for distributing these packets. It receives the data packets and deciphers where they need to go. Think of the network layer as a post office. The network layer uses protocols which are standard formats for communication between networked devices. The network layer uses TCP/IP address network protocols as its addressing system. ISP Data Packet

Internet Protocol Addresses (IP Address) Each server has what is called a unique Internet Protocol address (IP address). When a user types in a URL in their web browser the computer, the computer determines which server to use based on the IP address. Like a postal address, IP addresses allow computers to find each other. Everything connected to the internet directly or indirectly has an IP address (computers, servers, cell phones, etc…). Google.com IP address = Facebook.com IP address = Because the IP addresses are difficult to remember we name them such as Google.com and Facebook.com as shown above.

The Layers Layer 4: Transport Layer Most data being transferred is much to large. This is where the transport layer factors in. It breaks these large data packets into smaller packets so that they can be easily sent and reassembled when it reaches its destination. As it breaks down these large data packets into smaller ones and assigns it a sequenced number (Transmission Control Protocol) (TCP). It also ensures that all packets arrive at their correct destination. Routers work within the transport layer to assemble and reassemble data and send them to their correct location. Layer 5: Session Layer The Session Layer is responsible for opening, maintaining, and closing sessions between multiple applications and devices Sessions are conversations between applications and devices that communicate what and how data is going to be communicated. Layer 6: The Presentation Layer Converts data into universally readable formats. Since the evolution of standardized formats came along this is no longer relevant. Layer 7: Application Layer Used to exchange data on the network. Operating systems contain Application Program Interfaces (API) on their Application layer which allows the user to physically see what is on the screen. allows a computer’s network to interpret requests made by the program Software programs such as clients and web browsers that display what the network is communicating. Web page is displayed and retrieved!!!