Introduction - Computer Networks

• Theory
• Models
• Cryptography
• Socket Programming

Theory

• Communication
  • Input Message > Input Transducer > Transmitter > Channel > Receiver > Output Transducer > Output Message
• Bandwidth
  • Volume of data that can be transferred over a network
• Throughput
  • Indicates how much data was actually transferred from a source any given time
• Latency
  • Time it takes for the data to get to its destination across the network
  • Measured in terms of round trip time

Models

• TCP/IP
  • Developed by ARPANET
  • 4-Layer => Application Layer (Process to Process), Transport Layer (Host to Host), Internet Layer (Source to Destination), Network Access Layer (Node to Node)
  • 5-Layer => Application Layer, Transport Layer, Network Layer, Data Link Layer, Physical Layer
  • Support Client-Server and Peer to Peer
  • 
• Open Systems Interconnection (OSI) Model
  • Introduced in 1970, by International Standards Organization (ISO)
  • Trick
    • Please (Physical Layer)
    • Do (Data Link Layer)
    • Not (Network Layer)
    • Tell (Transport Layer)
    • Stupid (Session Layer)
    • People (Presentation Layer)
    • Anything (Application Layer)
  • OSI Model YouTube Video
  • 
  • 

Cryptography

• 
• CIA (Confidentiality, Integrity, Authenticity)
• Key
  • Symmetric => Using same keys for encryption and decryption
    • Encryption standards => DES, AES, 3DES
  • Asymmetric
    • Public & Private key
    • Encryption using receivers public key
    • No. of keys required in a network of N devices = 2*N
    • RSA Algorithm
      • Choose two different large random prime no.
      • Calculate, n = p * q and Ø(n) = (p-1) * (q-1)
      • Choose "e" such that 1 < e < Ø(n)
        • "e" is co prime to Ø(n), gcd(e, Ø(n)) = 1
      • Calculate "d" such that d * e = 1 mod Ø(n)
        • d * e = 1 + k * Ø(n)
      • Public key "e", Private key "d"

Socket Programming

• 
• Socket
  • Activates endpoint devices
  • Contains Domain (IPv6/IPv4), Type (TCP/UDP), Protocol
• Bind
  • Associates socket address (IP + Port)
• Listen
  • Waiting in Passive mode
  • Backlog => Pending requests in queue