ISDS 4120 Project 1 DWAYNE CARRAL JR 3/27/15

There are seven layers which make up the OSI (Open Systems Interconnection Model) which is the model for understanding and developing computer to computer communications. I'm explaining the process using these layers because the protocols and devices used in network connectivity are used throughout these processes.

In the application layer the customer types in the company's url ( into their internet browser and presses enter. If the customer is using Internet Explorer as their web browser Explorers API(application program interface) will transfer their request to the HTTP protocol. HTTP prompts lower-layer protocols to establish a connection between their computer and the webserver. Next, HTTP formats your request and sends “GET” request to tell the server which page they want to retrieve.

The Presentation Layer This layer often serves as a translator between data formats, such as various graphics file formats. It formats the data so that it can be read by different applications and hosts. It also performs coding and compression. The presentation layer is responsible for encryption and decryption in network communication. Basically in this layer it takes the data which is on the website that the customer views or receives and formats it so that it is viewable to them. Everything on the internet has a code which are represented by 1s ands 0s this is the computers language. It translates that language into our language so that we can see and view information. Encrypted message Binary Code Data Conversion Message Is decrypted

The session layer establishes the connection between two nodes for communication. One node will contact the other node to establish the connection. This would be the customer requesting access to our site. The receiving node will read the credentials and establish the connection. This is our site going through its authentication process. Once the session is open the customer can access everything we have available to them as the two nodes transfer information back and forth. The session layer keeps the session secure, synchronized and makes sure that only authorized nodes are connected to the session. Once the communication is finished, the session layer protocols will terminate the session. Node

The Transport layer protocols are responsible for delivering and verifying that the data arrives reliably, in the correct sequence and without errors. The transport Layer uses a protocol named TCP (Transmission Control Protocol) which is a connection oriented protocol that operates in the transport layer. Establishes a connection before sending data The customers computer sends a SYN packet to request a connection to the Web server. The Web server responds back with a SYN-ACK packet, or confirmation, to indicate that it is willing to make the connection. Then the customers computer replies back with it’s own ACK. A way to look at this process is when using a middleman to communicate and they ‘re going back and for the between parties. Once this connection is made, then the HTTP can request the Web page. To ensure integrity, connection oriented protocols, such as TCP, use a checksum. A checksum is a unique character string that allows the receiving node to determine if an arriving data unit exactly matches the data unit sent by the source. I think of this as the clerk at a dry cleaners checking to make sure that the customers receive the correct items of dry cleaning. Checksum

The Network Layer The primary function of the protocols in the Network layer is to translate network addresses into their physical counterparts and decide how to route data from the sender to the receiver. Each node on has two types of addresses. Network address – follow hierarchical addressing scheme and can be assigned through operating system software. Network addresses are also called network layer addresses, logical addresses or virtual addresses. Also known as an IP address (IPv4 or Ipv6) A network address is also a required component for connecting to the Internet. The IP address is what is used for communication. Without this its impossible for the customer to connect to the internet or for us to have how website available. Physical address – a fixed number associated with the device’s NIC; it is initially assigned by the manufacturer and stored on the NIC’s on-board memory. The NIC devices that enable a workstation, server, printer, or other node to receive and transmit data over the network media. The Physical Address is sometimes referred to as the Mac Address. The Mac address is the physical address located on the NIC which makes it unique to that NIC. Network layer protocols accept Transport layer segments and add logical addressing information in a network header. At this point, the data unit becomes a packet. Network layer protocols also determine the path from point A on one network to point B on another network by factoring in Delivery protocols, Network congestion, Quality of Service, Cost of alternative routes. Network CustomerServer

Data Link layer protocols divide data into distinct frames that can be transmitted by the Physical layer. It includes the raw data, or “payload”, as well as the network addresses of the sender and receiver and error checking and control information, which ensures the frame arrives without any problems. At the data link layer is where a switch operates which is a connectivity device that logically subdivides a network into smaller, individual collision domains. Switches can use the MAC addresses to transmit the data directly from our server to the customers Network without having to broadcast it to every computer attached to it. Server Switch Customers Network

The Physical Layer consists of the transmission medium (cables or wireless signals) that move the bits of data along the network. So in order for the customer to connect to our site its required for them to have some type of hub, switch, or router which is what connects everyone to the internet. An Ethernet connection is more than likely connected to one where as a wireless connection can connect multiple devices as long as they are within its range Ethernet Cable Router Hub

Referencing Dean, Tamara. Network Guide to Networks. 5th ed. Boston: Course Technology Cengage Learning, Print.