What are the layers in OSI Reference Models? Describe each layer briefly.
Answers
In the OSI model, control is passed from one layer to the next, starting at the application layer (Layer 7) in one station, and proceeding to the bottom layer, over the channel to the next station and back up the hierarchy. The OSI model takes the task of inter-networking and divides that up into what is referred to as a vertical stack that consists of the following 7 layers.
Application (Layer 7)
OSI Model, Layer 7, supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.
Presentation (Layer 6)
This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.
Session (Layer 5)
This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.
Transport (Layer 4)
OSI Model, Layer 4, provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.
Network (Layer 3)
Layer 3 provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing.
Data Link (Layer 2)
At OSI Model, Layer 2, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.
Physical (Layer 1)
OSI Model, Layer 1 conveys the bit stream - electrical impulse, light or radio signal — through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.
The open system interconnection(OSI) model defines a networking framework to implement protocols in seven layers. It was developed by international standard organisation(ISO). It divides the network communication system into seven layers. Layers 1-4 are considered as the lower layers, and mostly concern themselves with moving data around. Layers 5-7 are considered as the upper layers, and contain the application-level data. Networks operate on the basic principal of "pass it on." Each layer takes care of very specific job, and then passes the data onto the next layer.
Layer-1(Physical):
OSI model, the layer-1 conveys the bit stream - electrical impulse, light or radio signal- through the network at the electrical and mechanical level.
Layer-2(Data Link):
At OSI model, layer-2, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer.
Layer-3(Network):
Layer-3 provides switching and routing technologies, creating virtual paths, known as virtual circuits, for transmitting data from node to node.
Layer-4(Transport):
OSI model, Layer-4, provides transparent transfer of data between end systems, or hosts, and is responsible for end to end error recovery and flow control. It ensures complete data transfer.
Layer-5( Session):
This layer establishes, manages and terminates connections between applications.
Layer-6(Presentation):
This layer provides independence from differences in data representation by translating from application to network format, and vice versa.
Layer-7(Application):
The application layer is a layer in OSI Layer-7 model and in the TCP/IP protocol suit. It consists of protocols that focus on process-to-process communication across an IP network and provides a firm communication interface and end-user services.
Hope, it may help you to understand easily.................