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CN_5.MD

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OSI MODEL

Open System Interconnection

  • This is a reference model

  • 1970's & 80's

  • reference model for TCP/IP model

  • Protocols & Layered System

    • set up of some rules

  • Let us understand Layered system via diagram

    graph LR;
A[Location A] --> B[Location B]
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    • Seven Layers of OSI Model

      graph LR;
A[Application Layer]
B[Presentation Layer]
C[Session Layer]
D[Transport Layer]
E[Network Layer]
F[Data Link Layer]
G[Physical Layer]
      Loading
      • (Technique): All People Seems To Need Data Processing
graph LR;
A[Application Layer]-->B[Software Layer]
C[Presentation Layer]-->B
D[Session Layer]-->B
Loading 
graph LR;
A[Network Layer]-->B[HardWare Layer]
C[Data Link Layer]-->B
D[Physical Layer]-->B
Loading 
graph LR;
A[Transport Layer]-->B[Heart of the Model]
Loading 
graph LR;
A[Software Layer]<-->B[Transport Layer]<-->C[Hardware Layer]
B-->A
C-->B
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  • Application Layer
    • Provide User Interface Like Safari ,Chrome ,Brave
    • Provide Different Protocols for sharing the data
    • Ex: HTTP,FTP,SMTP
    • HTTP: Hyper Text Transfer Protocol(Website viewing)
    • FTP:File Transfer Protcol
    • SMTP:Simple Mail Transfer Protocol
    • HTTPS:Hyper Text Transfer Protocol Secure
graph LR;
A[Application Layer]--Data-->B[Presentation Layer]
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  • Presenatation Layer

    • Reformat the received data(Converting to ASCII Character)
    • Data Encrypting (AAA-->$#@@)(To save from hacking)
    • Data Compression(File size reduction)(less time more data transfer)

  • Session Layer

    • Create and Manage Session(Create Session for sender and Receiver will ready to authenticate and receive)
    • Add Check points (If connection interrupted then resending data from resumed point )
    • Terminate Session
graph LR; 
A[Presentation Layer]--Data-->B[Session Layer]--Data-->C[Transport Layer]
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  • - - >Transport Layer
  • If we are using whatsapp and youtube at same time how the system will identify which data is coming from which source so this is done by Transport Layer
  • Transport Layer uses port number and ip address to identify data source and by this bits data is differentiated
  • Threre is total 65,536 port numbers
graph RL;
A[Youtube]-- IP:208.65.153.238 -->B[Transport Layer]--Youtube Data-->D[User]
C[WhatsApp]--IP:157.240.229.60-->B
B-- Whatsapp Data -->D
A-- PORT: 80-->B
C-- PORT: 443-->B
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  • Transport Lyer also decides which Connection type should be used to transport data
  • TCP/UDP
    • If data will be transferred by TCP then this will be connection oriented protocol
    • TCP is connection oriented
    • UDP is connection less
    • In connection oriented model first connection is established then communication starts
    • In connection less model no conection is established just messages are sent
graph LR;
D[Data]-->A[Segment 1]
D-->B[Segment 2]
D-->C[Segment 3]
D-->E[Segment 4]
D-->F[Segment 5]
D-->G[Segment 6]
D-->H[Segment 7]
D-->I[Segment 8]
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  • Transport layer divides data in to segments

  • Convert data to segments

  • Flow Control

  • Error Control

  • Network Layer

    • Segments to packets

      • Each Packet go through different network before reaching the destination
      • Network Layer selects the quickest path for a packet to reach destination
      • Routers help the network layer in finding the best path
      • Network layer uses ip address to transfer a packet
      • once the ip address is assigned it will not change
      graph LR;
D[Segment]-->A[Packet 1]
D-->B[Packet 2]
D-->C[Packet 3]
D-->E[Packet 4]
D-->F[Packet 5]
D-->G[Packet 6]
D-->H[Packet 7]
D-->I[Packet 8]
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  • Data Link Layer

    • Packets to frames
    • how many frames that will be totally dependent on hardware used in data link layer
    • Mostly Hardware in data link layer is Network Interface Card(NIC)
    • NIC:
      • In which lan is connected
      • Swich and hub also work in this layer
    • In this layer to transfer the data we use MAC Address
    • And data is transferred system to system
    • Media Access Controller Layer
      • Desices which system will receive the media

  • Physical Layer

    • Decides how raw bits will be transferred through physical medium
    • If Physical Medium are wires then Electric Signal will be used to transmit data
    • If Wireless like wifi then radio signals will be used to transfer data
    • Physical Layer also decides the representation signal for 1 and 0 in a communication medium
    • Lifetime of a bt is also decided
    • Data rate also decided in this layer
    • also check mode of communication (simplex,half duplex,full duplex)
graph TD;
X[Sender]-->A[Application Layer]-->B[Presentation Layer]-->C[Session Layer]
C-->D[Transport Layer]-->E[Network Layer]
E-->F[Data Link Layer]-->G[Physical Layer]
H[Physical Layer]-->I[Data Link Layer]
I-->J[Network Layer]
J-->K[Transport Layer]
K-->L[Session Layer]
L-->M[Data Link Layer]
M-->N[Application Layer]
C--I am sending data-->L
L--par bhai tu hai kon -->C
C--Main ye le authenticate kar -->L
L-- Bhej de kar diya -->C
G-->H
N-->O[Receiver]
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TCP/IP Model

  • Follows two protocols
  • TCP:Transmission Control Protocol
  • IP:Interenet Protocol
  • Concern of that time we were able to comunicate Dell to Dell laptop 
    

    •