OSI 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 UTeM facilities. In this figure, a UTeM’s student is trying to access the Ulearn system located in the UTeM network facilities. The student is using her modem to connect to the public network before able to connect to the UTeM facilities. From the UTeM network, the data then was forwarded to IT Center where the Ulearn System server is located.

Students are required to suggest private addressing scheme used in UTeM network. Explain how you calculate the subnetting using FLSM based on the number of the faculties. The number of students of each faculty is within 500 – 1000 students. Each faculty is given their network address. Assign IT Center as another subnet with their own network address. From this network address, assigned as the 5^th available address as the address of the Ulearn System Server.

OSI Model 

Application Layer

The OSI model's uppermost layer is called the Application Layer. There are several ways to manipulate data or information in this layer, making it possible for any user to access the network. Requests for other sorts of information from the presentation layer are also made by this layer. In order to provide typical web application services, the Application Layer interface directly interacts with the application. This layer is essentially the top level of an open system that delivers services directly to the application development process. The OSI model's top-level layer, the Application Layer, serves a variety of essential services for all applications and communication processes. Files on a distant computer may now be accessed, retrieved, and managed by means of this extra degree of security. Also included in this layer is the ability for users to forward multiple emails, as well as a storage facility. Next, it deals with concerns such as network transparency, resource allocation, and so on. In this layer, users and application processes have access to network services.

Using the application tier, students connect to the online learning system's server from their own computers. At this level, students get direct access to the network. It is common for students to be given with many options after successfully signing in to a web-based learning system. When a student logs on to an online learning platform, they are welcomed with the website interface of the application layer. It is the application layer's responsibility to show and exchange data with users. The protocol manages data transfer and IP traffic. To communicate between a website and a web server, students utilize HTTP (Hypertext Transfer Mechanism), a common communication protocol. Others include FTP, DHCP and SNMP as well as Telnet and TelnetSSH.

Presentation Layer

Layer 6 of the Open Systems Interconnection (OSI) model is the presentation layer. It is used to convey data in an accurate, well-defined, and standardized manner to the application layer (layer 7). The syntax layer is another name for the presentation layer.

The presentation layer is in charge of the following actions:

• Data encryption/decryption

• Character/string conversion

• Data compression

• Graphic handling

The presentation layer is primarily responsible for converting data between the application layer and network format. Data can be conveyed in a variety of formats and from a variety of sources. As a result, the presentation layer is in charge of converting all formats into a common format for efficient and successful communication. The presentation layer adheres to data programming structure schemes created for various languages and offers the real-time syntax needed for communication between two objects such as layers, systems, or networks. The data format must be compatible with the subsequent levels; otherwise, the presentation layer may not function properly. Network devices or components used by the presentation layer include redirectors and gateways.

Transport Layer

The transport layer purpose is to provide functional and procedural means of transferring variable-length data sequences from one process to another. It ensure the communication is reliable by controlling flow control, error control and segmentation. Transport layer transmit data using transmission protocols including TCP and UDP. TCP are frequently used because of its reliability, it make sure the data sent reaches their destination and retransmit the data that failed to send. If no failures occurred, the transport layer will provide acknowledgment of the successful data transmission and deliver the following data. Meanwhile UDP is not reliable as TCP, it accept some data loss, reordering, errors or duplication but it sends data faster. The following is a summarization of transport layer functions:

• End-to-end delivery

• Addressing

• Reliable delivery

• Flow control

• Multiplexing

In this scenario, the transport layer delivers data using TCP because it ensures that the data delivered to the correct destination and in proper sequence. Firstly, TCP creates a connection with the ULearn System server. TCP breaks large data into smaller data packets to ensures the data integrity is intact once it is reassembled at the ULearn System server. Next, TCP will acknowledge what it received. TCP also will detect the lost packets and retransmit them.

Session Layer

Session Layer is the 5th layer in the Open System Interconnection (OSI) model. This layer allows users on different machines to established active communications sessions between them. It's responsible for establishing, maintaining, synchronizing, terminating, the sessions between end-user applications. 
In session layer, streams data are received and further marked, which is then resynchronized it properly, so that the ends of the messages are not cut initially and further data loss can be avoid. This layer basically establishes a connection between the session entities. this layer can handles and manipulates data which it receives from the Session Layer as well as from the Presentation Layer.
These are some of the functions which are performed by Session Layer:

• works as a dialog controller through which it allows system to communicate in either half-duplex mode full duplex mode of communication

• allows synchronization by allowing the process of adding checkpoints, which are considered as synchronization points to the streams of data

• responsible for synchronization information from different sources 

Network Layer

The network layer has two purposes. One method is to split segments into network packets and then reassemble them on the receiving end. The alternative method is to route packets across a physical network by determining the optimum path. To route packets to a destination node, the network layer needs network addresses (usually Internet Protocol addresses).

The network layer provides the functional and procedural means of moving variable length data sequences from one node to another in a separate network. Message delivery at the network layer does not guarantee that the network layer protocol is reliable. The following protocols are part of the layer management protocol:

• routing protocols

• multicast group management

• network layer address assignment

Routing protocol. Uses to determines the optimal network data transfer and communication links between network nodes using software and routing algorithms. Multicasting group management. To manage the effective routing of packets using multicast group addresses as a destination, a protocol is necessary. Network layer address assignment. The Network layer protocol translates logical addresses to MAC addresses.

Data Link Layer

Data Link Layer is responsible for the node-to-node delivery of the message. The main function of this layer is to make sure the data transfer is free from error from one node to another, over the physical layer. When a packet arrives in a network, it was the responsibility of DLL to transmit it to the host using its MAC address.
The packet that received from Network Layer is the further divided into frames depending on the frame size of NIC (Network Interface Card).
Data Link Layer divided into two sublayers:

• Logical Link Control (LLC)

• Media Access Control (MAC)

Functions of the Data Link Layer:

• Framing - provides a way for sender to transmit a set of bits that are important for the receiver.

• Physical Addressing - after creating frames, the data link layer adds physical addresses (MAC address) of the sender and/or receiver in the header of each frame

• Error control - provides the mechanism of error control in which it can detects and retransmits damaged or lost frames

• Access control - when a single communication channel is shared by multiple devices, the MAC sub-layer will helps to determine which device has control over the channel at a given time

Physical Layer

The physical layer is responsible for transmitting individual bits from one node to the next node. One of the duties of this layer is to represent the physical characteristics of interface and media. Besides that, it is also a representation of bits. The physical layer is responsible for condensing a network's hardware requirements in order to ensure data transmission success. For the physical layer level, network engineers can define different bit-transmission techniques, such as the forms and types of connectors, cables, and frequencies for each physical medium. The first layer of the OSI Model is the physical layer, which serves as the foundation for all higher-level processes. It converts data from the data-link layer (layer 2) into electromagnetic signals (binary data) for transmission through the physical medium (wired or wireless media). These signals could be digital (electrical pulses) or analogue (continuous electromagnetic waves).
The following services are provided by the physical layer:

• Modulates the process of converting a signal from one form to another so that it can be physically transmitted over a communication channel.

• Bit-by-bit delivery

• Line coding, which allows data to be sent by hardware devices that are optimised for digital communications that may have discreet timing on the transmission link.

• Bit synchronisation for synchronous serial communications.

• Start-stop signaling and flow control in asynchronous serial communication.

• Circuit switching and multiplexing hardware control of multiplexed digital signals.

• Carrier sensing and collision detection, whereby the physical layer detects carrier availability and avoids the congestion problems caused by undeliverable packets.

Protocols that make advantage of physical layers include:

• Digital Subscriber Line

• Integrated Services Digital Network

• Infrared Data Association

• Universal Serial Bus (USB)

• Bluetooth

• Controller Area Network

• Ethernet

When no physical link is made between the sender and recipient, transmission media can be either guided such as cables, fibre optics and UTP or unguided such as in the case of wireless connections. Physical layer also manages the data flow between a sender and a receiver by controlling the transmission rate.