• सुखार्थी त्यजते विद्यं विध्यार्थी त्यजते सुखम्सु sखर्थीन: कुतॊ विद्या कुतॊ विध्यार्थीन: सुखम् ||
  • “Luxury people leave knowledge, but a student leaves Luxury No knowledge for one who seeks Luxury, No luxury for student”
  • न चोर हार्यं न च राज हार्यं न भात्रू भाज्यं न च भारकारि |व्ययं कृते वर्धत एव नित्यं विद्याधनं सर्वधनप्रधानम ||
  • Cannot be snatched away by thief, cannot be snatched away by king, Cannot be divided among brothers, Not heavy either If spent daily, it always keeps growing. The wealth of knowledge is the precious of wealth of all”

OSI Model


Openn System Interconnection (OSI) model, an ISO standard for worldwide communication that defines a networking framework in seven layers. Layering the communications process means breaking down the communication process into manageable and interdependent categories.The convention and rules used in such communications are collectively known as layer. The model is developed by ISO (International organization for standardization) in Feb 1980. It is a set of protocols that allows any two different systems to communicate between different systems without requiring changes to the logic of the underlying hardware and software. The OSI model is not a protocol; it is a reference model for understanding and designing a network.

Physical Layer

Physical Layer defines the characteristics of the interface between the devices and the transmission medium. It also defines the type of transmission medium. It is layer 1 of OSI model.Responsibilities of the physical layer include the following

    1. Protocol Data Unit is Bits and Bytes
    2. It is responsibility of Network Infrastructure.
    3. Device which provides services to this layer are Repeaters, Passive Hubs, Patch Panels, Information outlet box, Cables, Network Interface Card, Gateways
    4. Protocol concerned with the layer are Ethernet, Token Ring.
    5. Layer defines Number of pins and functions of each pin of the network connector.
    6. Layer defines Signal level, data rate (electrical)
    7. Layer deals with physical properties of transmission medium.
    8. Layer deals with Representation of bits, Data rate and duration of bits.
    9. Layer deals with Synchronization of sender and receiver clock.
    10. Layer deals with Line configuration—point to point or multipoint, Physical topology
    11. Layer deals with Transmission mode– simplex or duplex

Data Link Layer

The data link layer is layer 2 of OSI model it  transforms the physical layer, a raw transmission facility, to a reliable link. Responsibilities of the data link layer include the following:

  1. Protocol Data Unit is Frame.
  2. Data flow is from HOP to HOP.
  3. Address used in data link layer is Physical Address / Link Address / MAC Address and its size is 48bits.
  4. It is responsibility of Network Infrastructure and deals with both Hardware and Software
  5. Device which provides services to this layer are Repeaters, Access Points,  Layer 2 Switch, and Gateways
  6. Protocol concerned with the layer are Ethernet and ATM.
  7. Layer deals with Flow Control Mechanism from hop to hop.
  8. Layer deals with shared media by defining MAC protocols.
  9. Layer deals in Error Detection and Correction Techniques.