Open Systems Interconnect

Introduction

The seven-layer OSI stands for Open Systems Interconnect reference model is a reparation of the way data travels through a network, it is an international standard for communication, the ISO reference model is divided into seven different layers, these are the application, the presentation, the session, the transport, the network, the data link, and the physical link.

Another reason for the ISO reference is to show the way that a device on a network communicates with another device, the data is spilled into packets since data is too big to transmit over a network. Networks are a collection of devices that are connected to a server or hub. The signal is needed to be converted into a digital format so that the computer can understand the information that is being transmitted, the data is changed into binary bits.

The three bottom layers of the model deal with moving the packets over the network to the end device, while the four top layers are used convert the data into packets and to complete the process of communion over the network. The model creates an outline of the interconnection of each layer and the relationships between the layers below and above the current layer.

Each layer is responsible for carrying out different functions and protocols for transmitting data on the network, these protocols are rules and procedures for commutation over the network. Each layer has different protocols that are needed for each layer to talk to one another. Standards are also used in the seven-layer model, these are rule and procedures that have been created by an organization or a governing body as a standard way of doing something, this is used so there isn’t lots of different way of doing something.

Image of the ISO model

1. Application layer. The application layer is the seven layers to the ISO model, this layer is used by the network applications, it makes use of the services and end-user processes, it allows the network to check user authentication and privacy, the layer also allows for file transfers, e-mail, and other network software services.[1] These processes are offered by a protocol that operates at the application layer, which is called the Hypertext Transfer Protocol (HTTP), telnet, Dynamic Host Configuration Protocol (DHCP) and File Transfer Protocol (FTP). This layer deals with email messages and files. It uses gateways to send information to the network layer.
2. Presentation layer. The Presentation layer data are formatted in a representation that the network can understand, it also deals with data encryption and decryption. the presentation layer works to transform data into the form that the application layer can accept. The data is translating from application to network format. This layer transforms data so that the layers below and above can understand what is being transferred and accepted it. The protocols used are AES encryption, American Standard Code (ASCII), Multi-Purpose Internet Mail Extensions (MIME). The devices used on this layer are firewalls and gateways.
3. Session layer. The session layer allows two applications on different computers to open, use, and close a connection, its main role is to perform name recognition and other functions, such as security, that are needed to allow two applications to communicate over the network, this layer coordinates and terminates conversations. the protocol used in this layer is remote procedure call (RPC), Structured Query Language (SQL) and ISO 8327. This layer used a device like gateways.
4. Transport layer. Transport layer this is where the data is transported via the network it uses to protocols Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) is a communications protocol used instead of TCP, it is used mainly for establishing low-latency connections between applications on the Internet. This layer checks for errors in the data once it arrives this means that the message is delivered error-free, in sequence, and with no losses or duplications. Gateways and multiplexers are devices used on this layer.
5. Network layer. The network layer is internet layer this is the layer that contains the packets information that will be transmitted. This layer decides which physical path the data should take based on network conditions, by using routers and gateways. The protocols used in this layer are Internet Protocol (IP), Network address translation (NAT), Address Resolution Protocol (ARP), Internet Control Message Protocol (ICMP), Internet Protocol Security is a network protocol suite that authenticates (IPSEC), Open Shortest Path First (OSPF).
6. Data Layer. The data layer sends data frames from the network layer to the physical layer. It is responsible for the control of the signals that enter and leave the network cable. On the receiving end, the data link layer packages raw bits from the physical layer into data frames. The layer also controls the data moving through this layer when no frame buffers are available. The protocols used in this layer are 802.11N, Spanning Tree Protocol (STP), Ethernet, Layer 2 Tunnelling Protocol (L2TP), Carrier-sense multiple access with collision detection (CSMA/CD) the protocol tells the network how to deal with to device trying to connect to the same data channel and how the device needs to wait to reconnect to the channel, to reduce the chance of collision in the network, Digital Subscriber Line (DSL) and Internet Protocol Security is a network protocol suite that authenticates (IPEC).
7. The physical layer. The physical layer is the bottom layer of the OSI sack transmits the unstructured raw data (signal state represents as 1 or a 0) over the physical medium like. The physical layer is hardware based and deals with all aspects of establishing and maintaining a physical link between communicating computers. This layer uses different types of cables E.G. wire, fibre, and wireless connection, the speed of transmission is dampened on the type of wires used and the speed of the area. The main protocols used on the physical layer are Fast Ethernet, Carrier-sense multiple access with collision detection (CSMA/CD) and Asynchronous transfer mode (ATM).

The protocols

This image shows how each layer of the ISO model is used and the different protocols and standards used on the layers. Some of the protocols used in the iso model are used on more than once. Protocols operate at the different layers of the OSI model. Each layer has its own protocols. TCP and IP are collectively called the protocol stack or the network/transport protocols. This is due to the protocols operating at the Network and Transport layers to make it possible for computers to communicate.

A protocol stack, r stack, is a group of protocols which are arranged in layers to enable communication. In the protocol stack, each layer provides services to the layer above it; and each layer also receives services from the layer beneath it. For two computers to partake in communications, each computer has to be running the same protocol stack. They can, however, have different operating systems.

• Layer 1, the Physical Layer: This layer deals with the hardware of networks such as cabling. The major protocols used by this layer include Bluetooth, PON, OTN, DSL, IEEE.802.11, IEEE.802.3, L431 and TIA 449.
• Layer 2, the Data Link Layer: This layer receives data from the physical layer and compiles it into a transformed form called framing or frame. The protocols are used by the Data Link Layer include ARP, CSLIP, HDLC, IEEE.802.3, PPP, X-25, SLIP, ATM, SDLS and PLIP.
• Layer 3, the Network Layer: This is the most important layer of the OSI model, which performs real-time processing and transfers data from nodes to nodes. Routers and switches are the devices used for this layer. The network layer assists the following protocols: Internet Protocol (IPv4), Internet Protocol (IPv6), IPX, AppleTalk, ICMP, IPSec, and IGMP.
• Layer 4, the Transport Layer: The transport layer works on two determined communication modes: Connection-oriented and connectionless. This layer transmits data from source to destination node. It uses the most important protocols of OSI protocol family, which are: Transmission Control Protocol (TCP), UDP, SPX, DCCP, and SCTP.
• Layer 5, the Session Layer: The session layer creates a session between the source and the destination nodes and terminates sessions on completion of the communication process. The protocols used are PPTP, SAP, L2TP, and NetBIOS.
• Layer 6, the Presentation Layer: The functions of encryption and decryption are defined on this layer. It converts data formats into a format readable by the application layer. The following are the presentation layer protocols: XDR, TLS, SSL, and MIME.
• Layer 7, the Application Layer: This layer works at the user end to interact with user applications. QoS (quality of service), file transfer and email are the major popular services of the application layer. This layer uses the following protocols: HTTP, SMTP, DHCP, FTP, Telnet, SNMP, and SMPP.

TCP vs UDP

Both TCP and UDP are protocols used for sending bits of data—known as packets—over the Internet. Both protocols build on top of the IP protocol. These packets are treated similarly, as they’re forwarded from your computer to intermediary routers and on to the destination.

TCP is tracked so no data is lost or corrupted in transit. This is why file downloads don’t become corrupted even if there are network hiccups. if the recipient is completely offline, your computer will give up and you’ll see an error message saying it can’t communicate with the remote host. Tcp is a reliable protocol and is used for the transfer of crucial data.

UDP is used when speed is desirable and error correction isn’t necessary. For example, UDP is frequently used for live broadcasts and online games. The server just sends a constant stream of UDP packets to computers watching. If you lose your connection for a few seconds, the video may freeze or get jumpy for a moment and then skip to the current bit of the broadcast. If you experience minor packet-loss, the video or audio may be distorted for a moment as the video continues to play without the missing data, it is an unreliable and connection-less protocol which is used for services that require fast transmission of data.

TCP/IP vs ISO model

Transmission Control Protocol (TCP) and Internet Protocol (IP) are two protocol that is linked together to create a reference model that is like the ISO model, each layer of the TCP/IP model has different functions that send information over the network. When information is sent over the Internet, it is broken up into packets so that the information can be sent over the network to the end device, where the packets are reassembled at the destination.

The TCP part of the model is used for creating the packets, putting them back together in the correct order so that the end device can use the information, and it also checks the packets to make sure that there aren’t any packets lost when the data transmission. Whiles the internet protocol is used to sending the information to the right network address. Each packet that is sent will contain the IP address showing where the packets are supposed to go. The TCP protocol verity’s the delivery of the packets. The layers include the Link Layer, the Internet Layer, Application Layer, and the Transport Layer. The OSI model is a reference tool, it is was the older one of the two model.

The TCP/IP model and OSI model are both models used for describing how the network communicates with network nodes, thought TCP/IP is an important protocol that used in all types of internet communication.