Data Communication and Networks basics for Computer Science and MCA students

Differentiate LAN, MAN and WAN.

Explain OSI layer in detail with neat diagram.

• OSI stands for Open System Interconnection model.
• It is a conceptual model that characterizes and standardizes the communication functions of a telecommunication without underlying their internal structure.
• It defines a networking framework to implement protocols in seven layers.
• In this model, control is passed from one layer to the next, starting at the application layer in one station and proceeding to the bottom layer.
• The OSI model is not tangible, it does not perform any functions in the networking process.
• It is a conceptual framework so we can better understand complex interactions that are happening.

• OSI model is a reference model for how applications can communicate over a network.
• It is a process of communication between two endpoints in a telecommunication network that can be divided into seven distinct groups of related functions or layers.
It has seven layers.



• The seven layers of OSI model are provided by a combination of applications, operating systems, network card device drivers and networking hardware which enables a system to put a signal on a network cable or other wireless protocol.

• Physical layer defines the physical characteristics of the network such as, connections, voltage level, light or radio signal, electrical impulse and timing.
• It is the level of the actual hardware.
• Fast Ethernet, RS232, FDDI and ATM are protocols with physical layer.
• Devices associated with the physical layer are: hubs, cables, connectors, repeaters, multiplexers, transmitters, receivers
• This layer is concerned with transmitting row bit's over communication channel.
• It conveys the bit stream through the network at the electrical optical or radio level.

• Data link layer sets up links across the physical network, putting packets into network frames.
• It has two sub layers:
I. Logic Link Control Layer
II. Media Access Control Layer
• Logic link control layer establishes and maintains links between communicating devices.
• Media access control layer controls the way multiple devices share the same media channel.
• The main function of data link layer are: framing, error detection and control, flow control.
• It provides mechanism to recover from lost, erroneous or duplicated data.
• Devices associated with data link layer are: bridges, intelligent hubs. Ethernet is the main data link layer in use.

• Network layer handles the addressing, error handling, congestion control, packet sequencing and routing of the data.
• It transfers the information between end systems across the communication subset.
• Examples of network layer are: IP, AppleTalk DDP, IPX.
• It provides switching and routing technologies, creating logical paths, which is known as virtual circuits for transmitting data from node to node.

• It is an end-to-end layer from the source to the destination.
• Transport layer ensures complete data transfer.
• Examples of transport layer are: TCP, UDP, SPX.
• It provides transparent transfer of data between end systems or host and is responsible for error recovery and flow control.
• Transport layer determines what type of service to provide to the upper layers.
• This layer take care of sequencing and reassembly.

• Session layer establishes, manages and terminates connections between applications.
• It allows users on different machine to establish sessions between them.
• Examples of session layer are: application interface, gateways, NFS, NetBios, RPC, SQL.
• Session layer deals with session and connection coordination.

• Presentation layer is part of an operating system.
• It converts incoming and outgoing data from one presentation format to another.
• Devices associated with presentation layer are: gateways
• Examples of presentation layer are: ASCII, JPEG, MPEG, EBCDIC etc.
• This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems.
• It is concerned with syntax and semantics of data transmitted, that means it defines the format of data to be exchanged between applications.
• Presentation layer sometimes called the syntax layer.

• Application layer supports application and end-user processes.
• It provides application services for file transfers, e-mail, remote terminal access, access to the World Wide Web and other network software services etc.
• Everything at this layer is application-specific.
• Examples of application layer are: Telnet, HTTP, FTP, WWW browsers, NFS etc.