How the Internet Works?

A presentation by Allison Green

Okay, here’s a scenario…

You’re sitting at a computer….

Type in www. yourcompany.com

As soon as you click on search your browser will ask your Operation System for your IP Address….

Well what exactly is an IP address?

You can think of an IP (Internet Protocol) address as a mail letter . It provides information about how and where data should be delivered, including the data’s source and destination addresses.

After the IP address is found (mailed) a DNS (Domain name server) will do a lookup. Once a DNS server finds the IP address of the website you are looking for, that IP address is returned to your browser.

Here’s a little more info about the DNS server…

Also within DNS lookups we use routers.

This device connects network segments and directs data based on information contained in the data packet. The router provides the WAN connections to LANS.

Next, your browser will now use the IP address returned by DNS to communicate with the web server that hosts the website that you want to visit. It will connect to port number 80 on the web server using a protocol called TCP.

Then, your browser opens a TCP connection to the destination host and

sends the request according to HTTP 1.1.

TCP simply is a connection-oriented protocol that establishes a connection before sending data. A protocol is a rule that governs how networks communicate. Protocols define the standards for communication between network devices. Without protocols, devices could not interpret signals sent by other devices and data would go nowhere.

Curious about HTTP?Hyper-Text Markup Language is the language that Web pages are written in. Web pages must conform to the rules of HTML in order to be displayed correctly in a Web browser.

After the browser opens the TCP to its Destination host, the browser receives HTTP response and may close the TCP connection, or reuse it for another request.

After the HTTP response is received the browser will display the HTML content

HTML or Hypertext Markup Language is a standardized system, for tagging text files to achieve font, color, graphic, and hyperlink effects on World Wide Web pages.

The content within the HTML includes images, CSS style sheets, JavaScript files and other various things that may be retrieved while uploading a site.

Finally the browser will send further asynchronous (state of not being synchronized) AJAX requests.

Asynchronous JavaScript & XML or simply AJAX in the final step of connecting to the browser sends data to the server in the background without interfering with the display and behavior of the existing page.

Furthermore in order for this entire series of steps to take place it is important that both your computer and the company’s computer has a of the requirements to be able to connect to the network…..

What’s required on the customer’s computer?

Most importantly you must have an Internet Service Provider according to the type of internet access that you are interested in for example: Dial-up vs Cable or Satellite

Once you are connected to the internet with an ISP (Internet Service Provider) a customer will need certain hardware that in addition to connecting them to the internet relates to layers within the OSI Model that I will further discuss in future slides…

Switch Router Ethernet cable

Network InterfaceCard (NIC)

Modem

What is the OSI Model?

The Open Systems Interconnection (OSI) Model is a model for understanding and developing network computer-to computer communications and is divided into 7 layers: Application, Presentation, Session, Transport, Network, Data Link & Physical.

Application

Presentation

Session

Transport

Network

Data Link

Physical

The Application Layer

Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software service. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.

7th layer of OSI Model

The Presentation Layer

6th Layer of OSI Model

The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.

The Session Layer5th Layer of OSI Model

This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.

The Transport Layer

4th Layer of the OSI Model

This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.

In addition: The TCP port number within the Transport layer provides an endpoint to a logical connection and the way a client program specifies a specific server program on a computer in a network

The Network Layer

3rd Layer of OSI ModelThis layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing.

I’ve already explained the duty of routers in a previous slide but switches (also referred to as local hubs) are connected to routers switch and serves as a controller, enabling networked devices to talk to each other efficiently. Through information sharing and resource allocation, switches save businesses money and increase employee productivity.

Switch Router

The Data Link Layer

2nd Layer of OSI Model

The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.

Network InterfaceCard (NIC)

Network Interface Cards (NICs) are installed in PCs. Network cables attach to the NICs. These cables run from the NIC in the PC to a jack on the wall.

On every NIC is a Media Access Control (MAC) or Ethernet Address which is a unique address burned into a ROM chip on the network card. Each MAC address is 12 hex characters or 48 bits in length

Ethernet cable

The Physical Layer

1st Layer of OSI Model

This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects

Router NetworkingCables

Network InterfaceCard (NIC) Switch

The End