Data Communication and Networks basics for Computer Science and MCA students

Differentiate LAN, MAN and WAN.

1.Stands for Local Area Network.Stands for Metropolitan Area Network.Stands for Wide Area Network.
2.It is a group of computer and other network devices which are connected together.It is a larger network of computers and other network devices which are connected together and usually spans over several buildings or large geographical area.It is a group of computers and other network devices which are connected together and which is not restricted to geographical location.
3.All the devices that are part of LANs are situated within multiple buildings or officesAll the devices that are part of MAN span across buildings or small town.All the devices which are part of WAN and have no geographical boundaries.
4.It has very high speed.It has lower speed compared to LAN.The speed is based on geographical location of the servers. It connects several LANs.
5.Connection speed can be 1Mbps or 100Mbps or 1000Mbps.Connection speed can be 10Mbps of 100Mbps.Connection speed can be 10Mbps or 100Mbps.
6.It uses guided media.It either uses guided media or unguided media.It uses guided media or unguided media. Its long distance communications, which may or may not be provided by public packet network.
7.It has smaller coverage range within the house or office premises.It has distance coverage and data rate higher than LAN, but less than WAN.It has larger coverage than LAN and MAN.
8.Example: Used by desktop and laptops for sharing the common resources such as printer, hard disk etc.Example: Local Cable TV system.Example: Telephone system, Internet

Explain OSI layer in detail with neat diagram.

What is OSI?
  • 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 Layer Model
  • 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.

    OSI Layer
  • 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.
Layer 1: Physical Layer
  • 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.
Layer 2: Data Link Layer
  • 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.
Layer 3: Network Layer
  • 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.
Layer 4: Transport Layer
  • 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.
Layer 5: Session Layer
  • 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.
Layer 6: Presentation Layer
  • 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.
Layer 7: Application 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.