Networking, Control Systems, DNS, and Cryptography Basics

Posted on Mar 12, 2026 in Contemporary Music Composition

IPv4 Header Structure

The IPv4 header is essential for routing packets across networks.

  • Version: 4 bits (IP version 4)
  • IHL: 4 bits (Header length in 32-bit words, min=5)
  • TOS/DSCP: 8 bits (Type of service / QoS priority)
  • Total Length: 16 bits (Header + Data, max 65535 bytes)
  • Identification: 16 bits (Unique ID for fragmentation)
  • Flags: 3 bits (DF: don’t fragment, MF: more fragments)
  • Fragment Offset: 13 bits (Position of fragment in original datagram)
  • TTL: 8 bits (Hop count limit; decremented at each router)
  • Protocol: 8 bits (Upper layer: TCP=6, UDP=17, ICMP=1)
  • Header Checksum: 16 bits (Error checking for header only)
  • Source IP: 32 bits (Sender’s IP address)
  • Destination IP: 32 bits (Receiver’s IP address)
  • Options: Variable (Security, routing)

IPv6 Header Structure

IPv6 simplifies the header for more efficient processing.

  • Version: 4 bits (IP version 6)
  • Traffic Class: 8 bits (QoS / priority)
  • Flow Label: 20 bits (Identifies packet flow for QoS)
  • Payload Length: 16 bits (Length of data after header)
  • Next Header: 8 bits (Type of next header)
  • Hop Limit: 8 bits (Decremented at each router)
  • Source Address: 128 bits
  • Destination Address: 128 bits

Control Systems

Open Loop Control System

Definition: Output has no effect on input. No feedback is used.

Diagram: Input → [Controller] → [Plant] → Output

Examples: Toaster, Fan, Traffic light, Washing machine

Closed Loop Control System

Definition: Output is fed back and compared with input to minimize error.

Diagram: Input → (Σ) → [Controller] → [Plant] → Output; Feedback loop returns to (Σ).

Examples: AC, Thermostat, Cruise control, Refrigerator

DNS (Domain Name System)

DNS is the “Phone book of the Internet”, converting domain names (e.g., www.google.com) into IP addresses.

How DNS Works

  1. User types domain in browser.
  2. Query goes to DNS Resolver (ISP).
  3. Resolver asks Root Server for TLD server address.
  4. Resolver asks TLD Server for Authoritative Server.
  5. Resolver asks Authoritative Server for the actual IP.
  6. IP returned to browser; connection established.

Cryptography Basics

Cryptography secures information by converting it into an unreadable form.

  • Symmetric Key: Uses the same key for encryption and decryption (e.g., AES, DES).
  • Asymmetric Key: Uses a public key to encrypt and a private key to decrypt (e.g., RSA, ECC).
  • Hash Function: One-way encryption with fixed-size output (e.g., MD5, SHA-256).

Subnetting Example (198.168.16.0/26)

To create 4 subnets from a /26 network:

  • New Prefix: /28
  • Hosts per Subnet: 14 usable
  • Subnet Mask: 255.255.255.240