According to the scenario, data is transmitted between OUM’s student who use the internet (Public IP) and the OUM IT Center, which uses Class C Private to interact on their LAN Network. During the data transmission between public and private IP addresses, a technological approach is used. The majority of public IP addresses are generated by a unique IP address provided by the ISP in order to communicate over the Internet. In this scenario, OUM's students and the main router in the OUM Network has an unique Public IP address for communicating on the internet, whereas the private IP address assigned to OUM Faculty and their hosts will communicate on the Internet through main router, which can access the Internet by requesting transmission from the router. The main factor why Private IP addresses cannot access the internet is that they are not unique on the Internet, and there are many hosts with the same IP address. Based on such concerns, if a user makes a request on www.google.com directly to the internet using a private IP, a problem may arise when the request is received from the Internet, where the host with the same IP Address worldwide receives the request. As a result, there will be some data collision. That is the primary reason why we do not utilise Private IP directly to connect to the internet.
OSI Layer Model
OSI model was established in 1947 by International Standards Organization (ISO).The OSI model is a conceptual framework used to explain and describe the function of networking system. In OSI reference model, the communication between a computing system are split to seven different abstraction layer. We are going to explain how the data travels from the student's computer to reach the Online Learning System server which is in the OUM IT center by OSI layer model. Below shows the brief explanation for seven layers of OSI model and duties or function for each layer:
7. Application Layer
The application layer is responsible for providing services to the end-user. This layer identifies communication partners, resource availability, and synchronizes communication.
6. Presentation Layer
The presentation layer is responsible to translate data based on the syntax and semantics that the applications accepted.
5. Session Layer
The session layer is responsible for maintains, establishes and synchronizes the interaction between communicating systems.
4. Transport Layer
The transport layer is responsible to delivery and error checking of data packets.
3. Network Layer
The network layer is responsible for receiving frames from the data link layer, and delivering frames to intended and specific destinations among based on the addresses contained inside the frame.
2. Data Link Layer
The data link layer is responsible to provides the function to transfer data between network entities and might provide the function of corrects errors that may have occurred at the physical layer.
1. Physical Layer
The physical layer is responsible for transmitting individual bits from one node to the next.
OSI Layer Model for Student Side:
This OSI Layer Model explanation will begin with an OUM student utilising their home network (public IP address) to connect to their private network's Online Learning System Server (Private IP Address). Assume an OUM student is attempting to upload a file to the OUM Online Learning System. Let's begin with the Application Layer, where the file that an OUM student wishes to upload into the OUM Online Learning System platform will be provided with data transit services such as SMTP, POP3, and so on. In this scenario, a file transfer protocol (FTP) is used to transport the data. The file will then be converted into binary form on the Presentation Layer, and file compression will commence in order to minimise the file's size. For an example a 7MB file will be compressed into 3MB, allowing the content to be sent even quicker. Finally, it will encrypt the file sent by the sender for data security purposes using SSL or another security protocol. The data will then be sent to the session layer, which will manage the communication session without causing any distortion between the communicating systems. For these three processes, the packet data unit is data, which will be broken down into segments in the following step. The segmentation begins on this transport layer. The source and destination port numbers as well as the sequence number, are included in each segment. The goal of the port number is to get the data on the right path, and the sequence number is to reorganise the segments that are out of order. Furthermore, error control is a key component of this layer, since it determines if the segments have arrived or not, and if they haven't, it will re-send them. TCP and UDP are the two protocols that are used in this procedure. TCP will be utilised to transmit the file in our scenario since TCP ensures that every data packet is sent and receives a message indicating whether or not the data has been reached. Why didn't we use UDP? Because most UDP is used for video streaming, and it doesn't respond to whether the data has been reached or not. The network layer is the next layer, which is where the important portions of our data journey are dependent on the situation due to communication between public and private IP addresses. The delivery of packets (PDU) from the original source (Sender) to the ultimate destination is the responsibility of this layer (Receiver). The processes involved in this layer include logical addressing, which assigns an IPv4 destination to each segment, and routing, which manages packet delivery depending on the IP address and subnet mask. The routing will be different in this case due to the public to private IP address, where the sender (Public IP address) will transmit the data to the OUM main router (Public IP address), and then another routing will occur inside the OUM Private IP Address to transmit the data to the requested host. The next layer is the data link layer, where the MAC address of the hardware is appended to the packet and the frame is formed. The goal of MAC is to keep track of data packets as they go from one Network Interface Card (NIC) to another via a shared channel (Hop-to-Hop Delivery). Finally, the physical layer is in charge of passing individual bits from one layer to the next. The physical layer also converts binary into a signal that can be sent via a medium. The media utilised in this scenario are wireless and wired media.
Below shows the way of how data transfer from OUM’s student side to the OUM server side using OSI layer model, the student is using her modem to connect to the public network before able to connect to the OUM facilities:
7. Application Layer
Student will access the system using the UI through application programs or website. When student want to access the system, data will be send. The protocol that the application layer uses to send command is https protocol and this layer (layer 7) will places a header field that contains information and passes the data to the Presentation layer (layer 6).
6. Presentation Layer
The data will be converted to machine-understandable binary format. This layer will also provide encryption and compression. In this case , this layer places header information and then pass the new data to the Session Layer (layer 5). The protocol involve is FTP, SSL and so on.
5. Session Layer
In this layer a header will be added to the data to handle the sessions. This layer is responsible for facilitating the starting, handling and ending of connections between nodes. After adding header, this layer will manage the data flow, and passes the data to the Transport layer (layer 4).
4. Transport Layer
Data is change or disintegration into segments that are reassembled by the transport layer at the server side. Each of the broken segments are sent to the Network Layer (layer 3) later on and also at this layer the source and destination port will also be specified. This layer is mainly responsible for flow control, fragmentation, port assigning and reliability. TCP is the best-known example of the transport layer.
3. Network Layer
This layer provides addressing across the internet and determines the path the data is to be sent that is routing happens in this layer. The segments will be given the source and destination IP address and the segments become packets. The packets will be then passed to the Data Link layer (layer 2).
2. Data Link Layer
This layer will place layer 2 header to ensure that the information is not corrupt, and then passes this new data, frame to the Physical layer (layer 1) for transmission.
1. Physical Layer
The bit stream is then transmitted as ones and zeros on this layer. It is at this point that the Physical layer ensures bit synchronization and bit synchronization will ensure the end-user data is assembled in the correct order it was sent. Examples of hardware in the physical layer are network adapters, ethernet, repeaters, networking hubs, etc.
OSI Layer Model for Server Side:
From the OUM’s student home modem to the OUM main router, the hop-hop delivery procedure now takes place. If the destination source is legitimate, this procedure only occurs from layer 1 to layer 3, after which it will proceed from layer 4 to layer 7. Start with the physical layer and work our way up to the application layer to decrypt the file that an OUM student uploaded. Firstly, on the physical layer where the data receive from the wired media, then it will proceed to next layer. Secondly, on the data connection layer, the source and destination MAC addresses are deleted, resulting in the frame becoming a packet. If a legitimate destination is identified at the network layer, the logical address will be deleted (packet to segments). If the destination is invalid, hop-to-hop delivery to the next node is used. On the transport layer, data (segment) will check the sequence addressing to see whether data has been misplaced during transmission, and port addressing will determine whether or not the destination has been reached using error control techniques. The session is ended at this session layer, and no additional conversation is allowed between the two parties; if additional conversation is required, a fresh request to begin a new dialogue session must be made. The data will be translated to its original form on the presentation layer, and the data will be decrypted using the same encryption mechanism used on the transmitting side. Finally, the authorization to read, write, and view the file sent by OUM’s student over the public network will be granted on the application layer.
Below shows the way of how data from the student's computer transfer from public network to the OUM server side using OSI layer model:
1. Physical Layer
The data from student is receiving at the server in IT center. This layer will read the bits from the physical medium and will convert them into frames and send to the Data Link Layer (layer 2). Examples of hardware in the physical layer are network adapters, ethernet, repeaters, networking hubs, etc.
2. Data Link Layer
In this layer, the data link headers will be removed. After removed, it will convert the frames back to packets and will pass to the Network Layer (layer 3).
3. Network Layer
In this layer, the IP address and header will be removed and will convert the packets change back to segments and pass them to Transport Layer (layer 4).
4. Transport Layer
As mentioned above, the segments will be reassembled back to the original data and uses the specific port number to determine the application that send the data. After finish the step, it will pass data to Session Layer (layer 5).
5. Session Layer
Uses the session information to determine which communication stream the data belongs to. After determination, it will pass the data to Presentation Layer (layer 6).
6. Presentation Layer
This layer uses the information passed by the session layer to interpret the data for the specific machine. The protocol involve is FTP, SSL and so on.
7. Application Layer
The application will read the https commands and give permission to the sender to achieve the website and finally student can access the Online Learning system.
Network Component For Data Communication
In order for the students to access the Online Learning System located in the OUM network facilities, network component is needed to connect student to the public network to connect the OUM facilities. Computer networks components comprise both physical parts as well as the software required for installing computer networks, both at organizations and at home. The hardware components are the server, client, peer, transmission medium, and connecting devices. The software components are operating system and protocols.
1) Message: The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video.
2) Sender: The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on.
3) Receiver: The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on.
4) Transmission Medium: The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.
5) Protocol: A protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating.
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