Day 5: Network Reference Models, OSI Model, TCP/IP Model

Hello Dear Students,
      Hope you all are doing good.....

Today's topic is Network Reference Models which is one of the most important topic from exam point of view.

Let's get started.....


A network is a set of nodes which are connected by communication links. The networks are connected by different entities. The standards are needed for the networks to communicate with each other. The 2 best-known standards are- 
  1. OSI Model
  2. Internet Model

THE OSI MODEL -  OSI stands for Open Systems Interconnection. The OSI model is the model that allows 2 different systems to communicate about their architectures. It allows open communication between different systems. OSI model is just a model and not a protocol. It is not used to install or run on any system. Basically there are 7 layers in OSI Model. 

LAYERS OF OSI MODEL
  1. Application Layer
  2. Presentation Layer
  3. Session Layer
  4. Transport Layer
  5. Network Layer
  6. Data Link Layer
  7. Physical Layer
Let's understand these layers, starting from the bottom -
  • PHYSICAL LAYER - It is the bottom layer in OSI model. This layer is responsible for the actual physical connections between 2 devices. However, The physical connections may be the wired/wireless mediums. It is responsible for the movement of individual bits from one node to the next. 
        Functions of Physical Layer
  1. Transforming bits into signals
  2. Bit Synchronization(by providing a clock)
  3. Provides physical characteristics of interfaces and medium.
  4. Bit rate control
  5. Line configuration(point-to-point/multi-point configuration)
  6. Transmission Mode
  7. Physical Topologies
  8. Multiplexing
  9. Circuit Switching
  • DATA LINK LAYER - It basically makes the physical layer error-free to the upper layer(i.e. Network Layer). This layer is responsible for moving of frames from one node to the next. 
        Functions of Data Link Layer-
  1. Framing
  2. Provides Physical Address to the frames
  3. Error Control
  4. Control flow of data from sender to receiver
  5. Access Control(when many devices attach to the same network)           
  6. Feedback
  • NETWORK LAYER - This layer is responsible for the source-to-destination delivery of a packet. If 2 systems are connected with different links then there is need of network layer, but if 2 systems are connected with same link, then there is no need of the network layer. 
        Functions of Network Layer
  1. Logical Addressing(adds a header to the packet, logical address)
  2. Routing
  • TRANSPORT LAYER - It is responsible for the source-to-destination delivery of the entire message. It makes sure that all packets of a message arrives in order. It provides the delivery of a message from one process to another.
        Functions of Transport layer
  1. Segmentation of message into packet and reassembly of packets into message.
  2. Connection Control
  3. Service-Point Addressing(or port address)
  4. Flow Control
  5. Error Control
  • SESSION LAYER - Session means the time which converts the data into information. It is basically responsible for the beginning, maintaining, and ending the communication between 2 devices. 
        Functions of Session Layer-
  1. Allows users to establish a connection called session between them.
  2. Authentication
  3. Dialog Control(Determines which device will communicate first and amount of data to be sent)
  4. Synchronization
  • PRESENTATION LAYER - It is basically concerned with the syntax and semantics of the information which is to be send. It is responsible for the format in which data is to be sent, the receiver can receive. As there are many encoding systems, thus this layer is responsible for inter-operatibility between different encoding systems.
        Functions of Presentation Layer
  1. Translation
  2. Data Encryption
  3. Data Compression
  • APPLICATION LAYER - It is the topmost layer of the OSI model. It is responsible for providing services to the users. It basically enables the user,(whether human/software) to access the network. It support for services such as Email, Remote file access, transfer, Database Management, etc.It basically uses FTAM(File Transfer, Access and Management) protocol.
        Functions of Application Layer-
  1. FTAM
  2. Mail services
  3. Directory Services
  4. Network Virtual Terminal(allows user to logon to remote host).

       previous years question paper questions

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previous years question paper questions

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previous years question paper questions

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TCP/IP REFERENCE MODEL - This model basically forms the base of the present day internet. This model was developed prior from the OSI model. The original TCP/IP protocol suite have 4 layers- 
  1. Host-to-Network Layer
  2. Internet Layer
  3. Transport Layer
  4. Application Layer
Compared with OSI model, we can say that,
  • Host-to-Network layer = Data link and Physical layer in OSI
  • Internet Layer = Network layer in OSI
  • Transport Layer = Transport layer in OSI
  • Application layer = Application layer in OSI 
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Some Protocols--
  • TCP/IP- Transmission Control Protocol/Internetworking Protocol
  • ARP- Address Resolution Protocol(associates logical address with physical address)
  • RARP- Reverse Address Resolution Protocol(discover IP from physical address)
  • ICMP- Internet Control Message Protocol(send query and error messages to the sender)
  • IGMP- Internet Group Message Protocol(transmission of messages to a group of receivers)
  • SCTP- Stream Control Transmission Protocol(provides support for newer applications such as voice over internet, etc.)
  • TELNET- Terminal Network(Used for remote login)
  • SMTP- Simple Mail Transfer Protocol(for Email)
  • FTP- File Transfer Protocol(for transfer of file from one system to another)
  • HTTP- HyperText Transfer Protocol(for fetching web-pages on WWW)
  • DNS- Domain Name Server(for mapping host names into network addresses)
  • NNTP- Network News Transfer Protocol(for news articles)





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