Question

C1) What is the main function of the OSI model? C2) Explain the major functions of the listed layers of the OSI model: (i) Application (ii) Transport (iii) Network (iv) Data Link (v) Physical C3) Explain the encapsulation process.

Answer 1

C1 )

Answer :

OSI Model

• OSI stands for Open System Interconnection is a reference model that describes how information from a software application in one computer moves through a physical medium to the software application in another computer.
• OSI consists of seven layers, and each layer performs a particular network function.
• OSI model was developed by the International Organization for Standardization (ISO) in 1984, and it is now considered as an architectural model for the inter-computer communications.
• OSI model divides the whole task into seven smaller and manageable tasks. Each layer is assigned a particular task.
• Each layer is self-contained, so that task assigned to each layer can be performed independently.

The OSI reference model describes how data is sent and received over a network. This model breaks down data transmission over a series of seven layers. ... The OSI model provides the standard for communication so that different manufacturers' computers can be used on the same network.

It is a generic model and acts as a guidance tool to develop any network model. It is a layered model. Changes are one layer do not affect other layers, provided that the interfaces between the layers do not change drastically.

C2 )

Answer :

Application Layer

At this layer, both the end user and the application layer interact directly with the software application. This layer sees network services provided to end-user applications such as a web browser . The application layer identifies communication partners, resource availability, and synchronizes communication.

Enables the user (human or software) to interact with the application or network whenever the user elects to read messages, transfer files or perform other network-related activities. Web browsers and other internet-connected apps, such as Outlook and Skype, use Layer 7 application protocols.

Transport Layer

The transport layer manages the delivery and error checking of data packets. It regulates the size, sequencing, and ultimately the transfer of data between systems and hosts. One of the most common examples of the transport layer is TCP or the Transmission Control Protocol.

Network Layer

The network layer is responsible for receiving frames from the data link layer, and delivering them to their intended destinations among based on the addresses contained inside the frame. The network layer finds the destination by using logical addresses, such as IP (internet protocol). At this layer, routers are a crucial component used to quite literally route information where it needs to go between networks.

The data-link layer

The protocol layer in a program that handles the moving of data into and out of a physical link in a network. This layer handles problems that occur as a result of bit transmission errors. It ensures that the pace of the data flow doesn’t overwhelm the sending and receiving devices. This layer also permits the transmission of data to Layer 3, the network layer, where it is addressed and routed.

The physical layer: Transports data using electrical, mechanical or procedural interfaces. This layer is responsible for sending computer bits from one device to another along the network. It determines how physical connections to the network are set up and how bits are represented into predictable signals as they are transmitted either electrically, optically or via radio waves.

C3 )

Answer :

When referring to networking, encapsulation is the process of taking data from one protocol and translating it into another protocol, so the data can continue across a network. For example, a TCP/IP packet contained within an ATM frame is a form of encapsulation.

When referring to programming, encapsulation is information in a module or section of code that enables the program or programmer to use code contained within a program.

Generally, Encapsulation is a process by which a lower-layer protocol receives data from a higher-layer protocol and then places the data into the data portion of its frame. Thus, encapsulation is the process of enclosing one type of packet using another type of packet.

Encapsulation at the lowest levels of the Open Systems Interconnection (OSI) reference model is sometimes referred to as framing. Examples of encapsulation include the following:

• An Ethernet frame that encapsulates an Internet Protocol (IP) packet, which itself encapsulates a Transmission Control Protocol (TCP) packet, which then encapsulates the actual data being transmitted over the network
• An Ethernet frame encapsulated in an Asynchronous Transfer Mode (ATM) frame for transmission over an ATM backbone