OSI Layer Model
How the data travels from the lecturer’s computer to reach the ULearn System server which is in the UTeM IT Center.
As we all know Open System Interconnection (OSI) Model defines and used for data to transferred from one computer to another in a computer network. In the most basic form, two computers connected to each other with WAN and LAN Cable and connectors for sharing data with the help of NICs forms a network. OSI have seven layers, which is Application layer, Presentation layer, Session Layer, Transport layer, Network layer, Data link layer and Physical Layer.
In this scenario, the data should travel from the lecturer’s computer to reach the ULearn System server which is in the UTeM IT Center. First, the lecturer’s data will go through the Application Layer, which is used by network applications to allow access to network resource. The lecturer is the end user and the server is the website. Using a web browser such as http, the lecturer initiates a request to the specified port on the server. The responding server stores resources, such as HTML files and images. This answering server is the origin server. There may be multiple middleware between the user agent and the origin server, such as agents, gateways, or tunnels.
Next, the lecturer’s request passed to
Presentation Layer, where it receives data from Application Layer, this data in
the form of characters and number. Presentation Layer will convert it to
machine understandable binary format. This function called translation, before
the data is transmitted, Presentation Layer will reduce the number of bits and
this is called as data compression and it can be lossy or lossless. Data
compression reduces the amount of file used to store the original file. As the
size of file is reducing, it can be receiving at the destination faster. To
maintain the integrity data, before transmission, data is encrypted. Encryption
enhance the security of sensitive data.
Next is the Transport Layer. Transport Layer controls the reliability of communication through flow control, error control and segmentation. In segmentation, data receives from session layer which divided into small data units called segments, each segments contains port number and sequence number. Port number will be directly to the right application. While, sequence number assembled in the correct order to form correct message at the receiver. There are two protocols in Transport Layer which is Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). Transport Layer performs two types of solution, which is Connection Oriented Transmission done by TCP, and Connectionless Transmission done by UDP. UDP is faster than TCP because it does not provide feedback whether data is delete, whereas TCP provide feedback, so we can trace the loss data. UDP used when it does not matter whether receives all data for example song, TFTP and DNS. TCP used when lecturer send full delivery is must, for example world wide web (WWW), email, FTP.
The Transport Layer sends data segments to the network layer. Network Layer works for the transmission of the received data segments from one computer to another located in different locations. Data Units in Network Layer is called Data-Packets. Function of network layer is logical addressing, routing and path determination.
Data link layer receives data packets from the network layer. Data packets contains IP addresses of sender and receiver. There are two types of addressing, which are Logical Addressing and Physical Addressing. Logical Addressing is done at network layer where sender and receiver’s IP addresses are assigned to each segments to form a data packets. Physical Addressing layer is done at data link layer where MAC addresses of sender and receiver are assigned to each data packets to form a frame. (MAC Address is 12-digit Alpha-Numeric Number) embedded in NIC over a computer. Data unit in data link layer is called Frame. Data link layer performs two basic functions, it allows opening layer OSI Model to access media using techniques framing. It controls how data is placed and received from the media using techniques such as Media Access Control and Error Detection.
Lastly, at Physical Layer, the data from Application Layer has been segmented by Transport Layer placed into Packets by Network Layer and Framed by Data Link Layer which is a sequence of binary 0's and 1's. Physical layer converts these binary bits into signals and transmit over local media. It can be an electrical signal in case of Copper cable or LAN cable, Light signal in case of Optical Fiber and Radio Signal in case of AIR. So signal generated by physical layer depends on the type of media used to connect two devices. At the receiver, Physical Layer receives signal and converts to bits and pass it to Data Link Layer as a Frame. Frame is further decapsulated as data moves through higher layers. Finally, data is moved to Application Layer. Application Layer Protocol makes the sender's message visible in the application in the receiver's computer screen. In this way, OSI model is helping to transfer data between different hosts. Therefore, these seven Layers of OSI model are lying behind the smooth functioning of Internet.
At the home network, we have PC and desktop computer. After
going through seven layers of OSI Model, it connects to modem because have
public IP address which can be accessed over internet. Modem used WAN connection.
While router, will distribute connection to PC and desktop computer in home
network. From IT Center, which there are server, will connect with router and
distribute connection to switch for all over departments. Switch cannot connect
directly from a network to another network. In this case, router is needed
because router can read IP address but switch cannot read IP address. Therefore,
when router passed the IP address, the switch can detect specific device, which
connected to it and know that the request are coming from UTeM lecturer.
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