Network Questions & Answer

1) What's the OSI reference model?

   OSI (Open System Interconnection) Reference Model is the systems that are open for coummunication with other systems.
   They are 7 Layers:

   Layer 1: Physical Layer 
                 The physical layer is concerned with transmitting raw bits over a communication channel.

   Layer 2: Data Link Layer
                The main task of the data link layer is to take a raw transmission facility and transform it into a line that appears free of undetected transmission errors to the network layer.

   Layer 3: Network Layer
                The network layer is concerned with controlling the operation of the subnet. A key design issue is determining how packets are routed from source to destination. It included the table lookup, forwarding and other protocols to help routing packets.

   Layer 4: Transport Layer
               The basic function of the transport layer is to accept data from the session layer, split it up into smaller units if need be, pass these to the network layer, and ensure that the pieces all arrive correctly at the other end.

   Layer 5: Session Layer
              The session layer allows users on different machines to establish sessions between them. A session allows ordinary data transport , as does the transport layer, but it also provides enhanced service useful in some applications.

  Layer 6: Presentation Layer
              The presentation layer performs certain functions that are requested sufficiently often to warrant finding a general solution for them, rather than letting each user solve the problems.

  Layer 7: Application Layer
             The application layer contains a variety of protocols that are commonly needed.

What's the function of Network layer?

The Network Layer is Layer 3 of the seven-layer OSI model of computer networking.
The Network Layer is responsible for end-to-end (source to destination) packet delivery including routing through intermediate hosts, whereas the Data Link Layer is responsible for node-to-node (hop-to-hop) frame delivery on the same link.
The Network Layer provides the functional and procedural means of transferring variable length data sequences from a source to a destination host via one or more networks while maintaining the quality of service and error control functions.

Functions of the Network Layer include:

• Connection model: connection-oriented and connectionless communication
• Host addressing
• Message forwarding