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]
  

  • 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]
    

    • (Technique): All People Seems To Need Data Processing

graph LR;
A[Application Layer]-->B[Software Layer]
C[Presentation Layer]-->B
D[Session Layer]-->B

graph LR;
A[Network Layer]-->B[HardWare Layer]
C[Data Link Layer]-->B
D[Physical Layer]-->B

graph LR;
A[Transport Layer]-->B[Heart of the Model]

graph LR;
A[Software Layer]<-->B[Transport Layer]<-->C[Hardware Layer]
B-->A
C-->B

• 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]

• 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]

• - - >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

• 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]

• 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]
    

• 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]

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
  • But not able to communicate Dell to Apple
  • So TCP/IP model was introduced