1. OSI LAYER MODEL

Project Scenario

The scenario of this project can be referred to Figure 1. Figure 1 shows the logical network flow from a home network to OUM facilities. In this figure, a OUM’s student is trying to access the OnlineLearning system located in the OUM network facilities. The student is using her modem to connect to the public network before able to connect to the OUM facilities. From the OUM network, the data then was forwarded to IT Center where the OnlineLearning System server is located.

Students are required to explain on how the data travels from the student’s computer to reach the Online Learning System server which is in the OUM IT Center. The explanation should be related the OSI Layer Model. Explain the possible network components involves throughout the communications. Illustrate the diagram to support your explanation. 

 a. OSI Model Layer

OSI model layer stands for open system interconnect was formalized by International Organization for Standardization in 1984. OSI is a reference tool for understanding how the data is communicated between any two-network system. Networking is complex so OSI model divides the complex functions of computer networks into seven different layers to easily understand the system.

            The OSI model consists of seven layer that start with physical layer, data link, network, transport, session, presentation and lastly the application layer as shown below. Data flows through the seven layers of the OSI model so that human-readable information can be transferred from a device to another end devices.

                   

 

Application Layer

The application layer contains the protocols used for process -to -process communication. The protocol specifies the format and control information required for normal Internet functioning.

A student in this scenario is to access into the Online Learning system located in the OUM network facilities. So, the student will see the website interface. This interface, which is the platform required for student to login into the Online Learning system is provided by the Applications layer. The main objective of the Application layer is to display the received information and provide data exchange services to user. Data exchange and traversed IP traffic are handled using protocols. The protocol used when student try to reach the Online Learning system servers is HTTP which is widely used throughout the World Wide Web for data transfer. 

Presentation Layer

The presentation layer offers a general representation of the data transferred between application layer services. In this layer, the information sent from the student’s computer will be standardized, and the encryption process will be completed if necessary. Then, it will decrypt when the data arrives at Online Learning system server. The encryption and decryption of the data are for security purposes. Then, the layer will compress the data to reduce the number of bits contained in the information and it will pass to the session layer. Compression will help increase the speed and efficiency of uploaded data.

Session Layer

            The session layer is the fifth layer which is responsible for dialog control and synchronization. This layer establishes, maintains, and synchronizes the interaction among communication systems.  It also allows a process to add a checkpoint to steam of data.

            A session is created when two systems which are student’s computer and Online Learning System in this scenario want to enter into dialog. The session layer will check the request made by application layer is available in local system or in remote system. When a student made a request. If the request is available in remote system, it test the availability of the computer’s network connection to access the resource. If the connection is not available, it will from the application layer an error message. But, when the network connection is available, it establishes a session with remote system. This session layer also terminate session if the communication is not available between two systems such as disconnected or timeout and also when the student finish accessing the system.

Transport Layer

            Transport layer is known as the heart of OSI layer because it builds on the network layer which is crucial to provide data transport from a process on  a source machine to a process on a destination machine. This layer takes data transferred in the session layer and breaks it into "segments" on the transmitting end, turning it back into data that can be used by the session layer. It is also hosted using single or multiple networks. In the other words, the transport layer deals with the data transfer coordination  between end systems and hosts. Furthermore, Transport Layer determines how much, where, and what rate data should be sent. This layer builds on the message which are received from the Application Layer. It also helps to ensure that data units are delivered error-free and in sequence. It controls the reliability of a link through flow control, error control, and segmentation or desegmentation. Additionally, this layer offers an acknowledgement of the successful data transmission and sends the next data in case no errors occurred.  Example of Transport Layer is the Transmission Control Protocol (TCP) which is built on top of the Internet Protocol (IP), commonly known as TCP/IP. TCP and UCP port numbers work at Layer 3 which is Network Layer. Therefore, routers at this layer help to do their functions efficiently.

 The Transport Layer may reassemble the data segmentation and control necessary into various communication streams. In this case, transport layer will track the student's communication between applications on the source and destination hosts. It is Transport layer's responsibility to maintain the multiple communication streams between these application of students and lecturers via online segments. It will then segment the data and managing into streams of application data.  Each piece of application data requires headers to be added at the Transport layer to indicate to which communication is associated. At the receiving host, each piece of data may be directed to the appropriate application. Additionally, these individual pieces of data must also be reconstructed into a complete data stream that is useful to the Application layer. The protocols at the Transport layer describe the how the Transport layer header information is used to reassemble the data pieces into streams to be passed to the Application layer.

 

            In order to pass data streams to the proper applications, the Transport layer must identify the target application. To accomplish this, the Transport layer assigns an application an identifier. The TCP/IP protocols call this identifier a port number. Each software process that needs to access the network is assigned a port number unique in that host. This port number is used in the transport layer header to indicate to which application that piece of data is associated. The Transport layer is the link between the Application layer and the lower layer that are responsible for network transmission. This layer accepts data from different conversations and passes it down to the lower layers as manageable pieces that can be eventually multiplexed over the media. Applications do not need to know the operational details of the network in use. The applications generate data that is sent from one application to another, without regard to the destination host type, the type of media over which the data must travel, the path taken by the data, the congestion on a link, or the size of the network. Additionally, the lower layers are not aware that there are multiple applications sending data on the network. Their responsibility is to deliver data to the appropriate device. The Transport layer then sorts these pieces before delivering them to the appropriate application.

 Because of different applications have different requirements, there are multiple Transport layer protocols. For some applications, segments must arrive in a very specific sequence in order to be processed successfully.

Network Layer

            Layer 3 is network layer. The network Layer controls the operation of the subnet. The main aim of this layer is to deliver packets from source to destination across multiple links (networks). If two computers (system) are connected on the same link, then there is no need for a network layer. It routes the signal through different channels to the other end and acts as a network controller. It also divides the outgoing messages into packets and to assemble incoming packets into messages for higher levels. In broadcast networks, the routing problem is simple, so the network layer is often thin or even non-existent.

            The student send the data from their computer to Online Learning system. The data that send from student actually send by packet to the Online learning in IT center. The packet is broken up into the smaller pieces when the data reach at Online learning in IT center. The network that use by student is home network by using different LAN with IT center that using OUM campus network, when student want to send the data, the network must be addressed by computer (IP Address) before the data can reach the IT center. The IP address which is the source, and Online learning in IT center is the destination that the data reach.

Data Link Layer

            Data link layer provides node-to-node data transfer, framing, physical addressing, flow control, access control and also handles error correction from the physical layer. There are two sub-layers in this layers which is Media Access Control (MAC) layer and Logical Link Control (LLC) layer. The MAC address layer allows the data link layer to provide the best data transmission vehicle and manage data flow control. The LLC layer provides error control and flow control over the physical medium and identifies line protocols.

            In physical addressing, the data link layer add a header to the frame in order to define physical address of the sender receiver of the frame. In framing, the data link layer receives the packets from the network layer divides into manageable data units called frames depending on the frames size of NIC (Network Interface Card). In access control, data link layer provide protocol to determine which device has control over the link at any given time when the student's computer and the modem are connected into the same link.

Physical Layer

            Position of physical layer in OSI Model layer is the lowest layer than other layers. Physical layer is electrical or physical devices that can send the data to others device such as fiber optic wire, NIC (network interface card), wireless access point, modem and router. At this layer, it responsible to transmit the bits from the source devices or from sending devices over the network communications media to receiver or destination devices. 

            Based on this project scenario, in physical layer, there have five network components that used when transmitting the data to the next destination which are NIC (1), wireless access points (1), modem (1), router (1) and switch (1). NIC (Network Interface Card) operates as control the exchange information between network and user. In this case, NIC allows communication between student’s PC and wireless access point. It means that it allow student’s PC connected to her WIFI first via modem then connect via local area network (LAN). 

            When student open the web page of Online Learning System, student’s PC will pass the request to the network card which convert it into electrical signal. This electrical signal will carry the individual bits from one node to next node through transmission medium. This process will deliver the bits to the data link layers. The data are sent via coaxial cable network to deliver to router. The router will send data to cloud over the internet before the data send to OUM network server and IT Center. OUM server will received the data by router over the internet and responds by sending the data back to router to send the data to IT Center. IT Center receive the data by router and will respond by sending the web page of Online Learning System back to the network card as synchronization of bits that form in electrical signal. NIC card get this signal and translates it into the data that can student’s PC display the web page Online Learning System.