‫I don't want to spend too much time on theoretical information, but to understand the packets sent
‫to the destination systems and the reply packets as well, we should talk about the TCP IP Internet
‫Protocol suite.
‫OCI open systems interconnection.
‫Is a reference model for how applications can communicate over a network, a reference model is a conceptual
‫framework for understanding relationships.
‫The purpose of the OCI reference model is to guide vendors and developers so that the digital communication
‫products and software programs they create will interoperate and to facilitate clear comparisons among
‫communications tools.
‫Most vendors involved in the telecommunications make an attempt to describe their products and services
‫in relation to the OCI model.
‫And although useful for guiding discussion and evaluation, OCI is rarely actually implemented.
‫As few network products or standard tools keep all related functions together in well-defined layers
‫as related to the model developed by representatives of major computer and telecommunication companies
‫beginning in 1983, Osai was originally intended to be a detailed specification of actual interfaces.
‫Instead, the committee decided to establish a common reference model for which others could then develop
‫detailed interfaces, which in turn could become standards.
‫Osai was officially adopted as the international standard by the International Organization of Standards
‫ISO.
‫So what about the Oh as I layers?
‫The main concept of Osai is that the process of communication between two end points in a telecommunication
‫network can be divided into seven distinct groups of related functions or layers.
‫Each communicating user, a program is at a computer that can provide those seven layers a function.
‫So in a given message between users, there will be a flow of data down through the layers in the source
‫computer across the network and then up through the layers in the receiving computer.
‫The seven layers of function are provided by a combination of applications, operating systems, network
‫card device drivers and networking hardware that enable a system to put a signal on a network cable
‫or out over Wi-Fi or any other wireless protocol.
‫The seven open systems interconnection layers are.
‫Layer seven, the application layer.
‫This is a layer at which communication partners are identified.
‫Is there someone to talk to?
‫Network capacity is assessed.
‫Will the network let me talk to them right now and.
‫That creates a thing to send or opens the thing received.
‫Please note that this layer is not the application itself.
‫It is this set of services and applications should be able to make use of directly, although some applications
‫may perform application layer functions.
‫Layer six, the presentation layer, this layer is usually part of an operating system and converts
‫incoming and outgoing data from one presentation format to another.
‫For example, from clear text to encrypted text at one end and back to clear text at the other.
‫Layer five, the session layer, this layer sets up coordinates and terminates conversations.
‫Services include authentication and reconnection.
‫After an interruption on the Internet Transmission Control Protocol, TCP and user data Graham Protocol
‫UDP provide these services for most applications.
‫Layer four, the transport layer, this layer manages packet ization of data, then the delivery of
‫the packet, including checking for errors and the data once it arrives.
‫On the Internet, TCP and UDP provide services for most applications as well.
‫Layer three, the network layer, this layer handles the addressing and routing of the data, sending
‫it in the right direction to the right destination on outgoing transmissions and receiving incoming
‫transmissions at the packet level.
‫IB is a network layer for the internet.
‫Layer two, the data link layer.
‫This layer sets up links across the physical network, putting packets into network frames.
‫This layer has two sub layers, the logical link control layer and the media access control layer.
‫Ethernet is the main data link, layer and use.
‫Layer one, the physical layer, this layer conveys the bitstream stream through the network at the
‫electrical, optical or radio level.
‫It provides the hardware means of sending and receiving data on a carrier network.
‫Let's see some of the most famous protocols of the layers.
‫For ease of use, it's better to talk about physical layer and data link layer together.
‫Here we have some protocols and data link layer and some physical media and connection methodologies
‫in physical layer Ethernet and 8.2.1 one wireless LAN are the most known protocols of the data link
‫layer.
‫Ethernet is the name of the most commonly used network protocol that controls how data is transmitted
‫over land, which is a local area network.
‫You need to have network interface cards in the devices that you want to connect to the network.
‫A wireless local area network, W LAN is a wireless computer network protocol that links two or more
‫devices using wireless communication within a limited area such as a home school, computer, laboratory
‫or office building.
‫This gives users the ability to move around with a local coverage area and yet still be connected to
‫the network.
‫Most modern LANs are based on I Tripoli 8.2.1 one standards and are marketed under the Wi-Fi brand name.
‫IP Internet Protocol is responsible for addressing host encapsulating data into transferred packet and
‫routing packets from a source host to a destination host across one or more IP networks.
‫The best known transport protocol is the transmission control protocol, or TCP.
‫It's used for connection oriented transmissions, whereas the connection less user data grand protocol
‫UDP is used for simpler messaging transmissions.
‫We're going to talk more in-depth about these protocols in the next lecture.
‫Again, for ease of use, the last three layers session, layer, presentation, layer and application
‫layer are thought of together as the application layer.
‫Let me put another parenthesis here.
‫We're talking about the OSAI reference model here.
‫In addition, there is another reference model called TCP IP reference model and instead of OSAI models
‫last three layers.
‫There is only a single application layer in the TCP IP reference model.
‫Just keep that in the back of your mind.
‫And back to our subject.
‫The application layer protocols are classified according to the protocol they are using in the transport
‫layer and these protocols in Iraq with the end user via applications.
‫Therefore, they are the most known protocols by just about everybody.
‫Some of the most well-known TCP based application layer protocols are.
‫HTP Hypertext Transfer Protocol, simply a communications protocol used to send and receive Web pages
‫and files on the internet.
‫Telnet is one of the simplest ways to exchange data between two computers.
‫It allows two computers anywhere on a computer network, including the worldwide internet, to exchange
‫text and, well, other data in real time.
‫FTP file transfer protocol is a communication protocol for the rapid, simple transmission of files
‫across a network.
‫SMTP.
‫Simple Mail Transfer Protocol is used to send and relay an e-mail message between e-mail servers.
‫Note that it is not used to retrieve email messages from a server.
‫Instead, either IMAP or Pop is used to retrieve email messages.
‫DNS, the domain name system is a system used to convert a computer's hostname into an IP address on
‫the internet.
‫For example, if a computer needs to communicate with a web server, NHS Dot UK, your computer needs
‫the IP address of the web server.
‫NHS Dot UK It is the job of the DNS to convert the hostname to the IP address of the web server.
‫The DNS uses both the UDP and TCP.
‫SNMP Simple Network Management Protocol is used in network management systems to monitor status of devices
‫and also spot problems.