1. OSI LAYER MODEL

The OSI Model

 (Open Systems Interconnection Model)  

    The OSI model (Open System Interconnection Model) is a conceptual framework that used to describe seven layers that computer systems use to communicate over a network. It was the first standard model for network communications, adopted by all major computer and telecommunication companies in the early 1980s. The OSI was published in 1984 by the International Organization for Standardization (ISO).

    The OSI model characterizes computing functions into a universal set of rules and requirements in order to support interoperability between different products and software. In the OSI reference model, the communications between a computing system are split into seven different abstraction layers as shown picture above: Physical, Data Link, Network, Transport, Session, Presentation, and Application. Though it does not always map directly to specific systems, the OSI Model is still used today as a means to describe Network Architecture.

📨 Layer 1 : Physical Layer 

    The physical layer is responsible for the actual physical connection between the devices. Figures above shows the transmission of bits in physical hardware. The physical layer contains information in the form of bits. It is responsible for transmitting individual bits from one node to the next. When receiving the data, this layer will get the signal received and convert it into the form of 0 and 1 and send them to the Data Link Layer, which will put the frame back together.

Duties of Physical Layer 📌

✅ Physical characteristic of interface and media

✅ Representation of Bits

✅ Bit Synchronization

✅ Bit rate control

✅ Transmission mode

✅ Devices must be connected using topologies

📨 Layer 2 : Data Link Layer 

    Data link layer is the protocol layer in a program to handles the moving of data into and out of the physical link in the network. Data link layer has worked between two hosts that are directly connected in some sense. The direct connection could be a point to point or broadcast. The data link layer is responsible for transmitting frames from one node to next. 

 Duties of Data Link Layer 📌

✅  Enables data movement over a link from one device to another

✅  Media access control.

✅  Packet addressing.

✅  Formatting the frame that is used to encapsulate data.

✅  Error notification on physical layer.

✅ It orders bits and packets to and from data segments. This ensuing result is called as frames. They contain data that are set in an orderly manner.

✅ Ensure error-free communication between two devices by correct transmission of frames.

📨 Layer 3 : Network Layer 

    The network layer is the third layer in OSI Model. The network layer can define the communication over of the network with four basic processes which are addressing, routing, encapsulation and decapsulation. The main responsibilities of the network layer is to move packets from sending hosts to receiving hosts.

 Duties of Network Layer 📌

✅ Responsible for establishing paths that are used for the transfer of data packets between network devices.

✅  Traffic direction.

✅  Addressing; Service and logical network addresses.

✅  Routing.

✅  Packet switching.

✅  Controlling packet sequence.

✅  Complete error detection; from sender to receiver.

✅  Congestion control.

✅  Gateway services.

📨 Layer 4 : Transport Layer 

    Transport layer is the layer that provides the means of transferring data sequences (packets) from the source to a destination (from a client to a server or vice versa) and while maintaining quality of service functions (i.e priority queuing and bandwidth management).Transport layer is responsible for delivery message from one process to another. TCP and UDP are the common transport protocols used at this layer.

 Duties of Transport Layer 📌

✅ Responsible for message delivery between the networked hosts. Messages are fragmented and reassembled by this layer. It also controls the reliability of any given link.

✅ Guaranteed delivery of data.

✅ Name resolution.

✅ Flow control.

✅ Error detection and recovery.

📨 Layer 5 : Session Layer 

    The session layer is responsible for maintains, establishes and synchronizes the interaction between communicating system. The session layer controls the connections between hosts, or computers. It establishes, manages and terminates the connection between the local and the remote application (servers). It provides full-duplex (input and output at full speed) , half-duplex (only input or output one at a time) or simplex (only receive or transmit). Session layer is also responsible for procedures such as checkpointing, suspending, restarting and terminating a session. It is also responsible for gracefully closing a session. Nowadays, it is replaced by tcp/ip system and the session is non existent and part of the tcp protocol.

 Duties of Session Layer 📌

✅ Establish, monitor and terminate the communication session between applications.

✅ Name lookup, security functions and data synchronization.

✅ Placement of header information in a packet.

✅ Determines whether the messages that are exchanged during a session are full or half duplex.

📨 Layer 6 : Presentation Layer 

The presentation layer is responsible for syntax and semantics of the information exchanged between two systems. It also will translate, encrypt and compress data. 

Translation → The running programs must be changed to bit streams before being transmitted 

Encryption/Decryption → To carry sensitive information, a system must be able to ensure privacy

Compression → Reduces the number of bits contained in the information. 

 Duties of Presentation Layer 📌

✅ This layer defines the syntax used by hosts in the network to communicate.

✅ Data compression.

✅ Encryption and decryption of data.

✅ Data translation.

✅ Interpreting graphics commands.

✅ Protocol conversion.

✅ Gateway services.

📨 Layer 7 : Application Layer 

    The application layer is responsible for providing services to the user. This is the only layer that directly interacts with data from the user. Software applications like web browsers and email clients rely on the application layer to initiate communications. But it should be made clear that client software applications are not part of the application layer; rather the application layer is responsible for the protocols and data manipulation that the software relies on to present meaningful data to the user. 

 Duties of Application Layer 📌

✅ It works as an interface between the software and the network protocol on the computer. It provides services that are necessary to support the applications.

✅ This layer provides interface for FTP applications, email and telnet.

✅ Mail Services 

✅ File transfer and access

✅ Remote Login

✅ Accessing WWW

 Common Protocol in Application Layer 📌

✅ File Transfer Protocol (FTP).

✅ Simple Mail Transfer Protocol (SMTP).

✅ Internet Message Access Protocol (IMAP).

✅ Hypertext Transfer Protocol (HTTP).

✅ Post Office Protocol (POP).

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"In this section, you are expecting to explain on how the data travels from the student’s computer to reach the Ulearn System server which is in the UTeM 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."

When sending the data or information from one device to end device, the data will travel in 7 layer of OSI model. After that, it will travel up using 7 layer on the receiving end. 

Figures above shows the possible network components involved throughout the communication 

    For example of the situation, student is using Online Learning System to submit the assignment or task to their lecturers. The procedure will began on the student's PC. The assignment which can be called as raw data, will be passed to the application layer (Layer 7) by the file application when the students upload the assignment file. The data format and File Transfer Protocol (FTP) will be defined on the application layer, and the data will be passed to the next layer, presentation layer. 

    On layer 6 which is presentation layer, the data format will be standardized and the encryption process will be completed if it was necessary by referring to the communication connection type whether it is encrypted or not. Next, the presentation layer will compress the data and pass it to the session layer. This compression process will help improve the speed and efficiency of the uploaded data. 

    After that, on layer 5 which is session layer, the communication session will be initialized by sending request and responses between the application layer and the transport layer. This process is to determine whether the requested session is legitimate or not. If it is legitimate, the data will be pass to the next layer. 

    The data is passed to the layer 4 which is transport layer. The transport will provide multiplexing, enables the host to send and receive error corrected data through the implementation of TCP and UDP protocols. The flow and error control will be performed, thus the data will be segmented then broken up into packets 

at the network layer. 

    On layer 3 of OSI model, network layer will facilitate the data transferred and ensure whether the network layer is necessary or not by checking the device communicating on the same network or not. Next, the network layer will route the packets to reach its destination using the best physical path which called as routing process that occurred at the router. 

    When the packets passed to layer 2, data link layer, it will be broken down into frames and delivered to the layer 1, physical layer. The frames will be converted to a bitstream of 0s and 1s and send through a physical medium which WLAN. Then, the data will be stored in the Ulearn System server that is located in the UTeM IT Centre.