Computer Networks – Introductory Principles & Architecture

Course Outcomes

  • Upon completion of the course, a student will be able to:
    • Interpret the individual building blocks of a communication network and their overall architecture.
    • Contrast circuit-switched and packet-switched networks and quantitatively analyze network performance.
    • Identify, evaluate, and design error- and flow-control mechanisms that operate in the Data-Link layer.
    • Perform IPv4 subnetting and analyze Network-layer performance when using different routing protocols.
    • Compare congestion-control techniques and select suitable Transport-layer protocols (with security enhancements) for real-time applications.

Module Structure & Contact Hours

  • Module 1: Networking Principles & Layered Architecture – 6 hrs
  • Module 2: Circuit & Packet Switching – 7 hrs
  • Module 3: Data-Link Layer – 8 hrs
  • Module 4: Network Layer – 8 hrs
  • Module 5: Routing Protocols – 6 hrs
  • Module 6: Transport Layer – 5 hrs
  • Module 7: Application Layer – 3 hrs
  • Module 8: Contemporary Issues – 2 hrs

Reference Material

  • Textbook: Behrouz A. Forouzan, Data Communication and Networking (5th Ed., 2017, McGraw-Hill).
  • Additional references:
    • Kurose & Ross, Computer Networking – A Top-Down Approach (6th Ed.).
    • Stallings, Data and Computer Communication (10th Ed.).
  • Evaluation: CAT, written assignments, quizzes, Final Assessment Test (FAT).

Communication vs. Data Communication

  • Communication: Transfer of information (voice, data, video) over wired or wireless media.
  • Data Communication: Exchange of data between two devices using a transmission medium (e.g., copper wire, fiber). Key term telecommunication implies “communication at a distance.”
  • End nodes can be PCs, printers, cameras; intermediate nodes include switches, routers, and the Internet cloud.
  • Primary goal: resource sharing (files, printers, web access) through an agreed architecture (physical + logical design).

Fundamental Characteristics of a Data-Communication System

  • Delivery
    • Data must reach the correct destination device/user, and only that device/user.
  • Accuracy
    • Information must arrive unaltered; corrupted bits render data unusable.
  • Timeliness
    • Especially for voice/video, data must arrive when expected (real-time constraints).
  • Jitter
    • Variation in packet inter-arrival time; e.g., if video frames intended for 30\,\text{ms} spacing arrive sometimes at 30\,\text{ms} and other times at 40\,\text{ms}, perceptible quality degradation occurs.

Five Core Components of a Data-Communication Model

  1. Message – The actual information (text, images, audio, video).
  2. Sender – Device initiating transmission (PC, workstation, telephone, camera).
  3. Receiver – Endpoint that accepts the message (computer, TV, printer).
  4. Transmission Medium – Physical path: twisted-pair, coaxial, fiber-optic, free-space radio, etc.
  5. Protocol – Formal set of rules enabling interoperability. Without matching protocols, connected devices cannot communicate (analogy: French vs. Japanese speakers with no common language).

Data-Flow Directions

  • Simplex – Unidirectional; e.g., keyboard → computer, monitor ← mainframe.
  • Half-Duplex – Bidirectional but not simultaneous; devices alternate roles (walkie-talkies).
  • Full-Duplex – Simultaneous two-way transfer; requires either two physical links or echo cancellation (telephone conversation).

Network Definition & Line Configurations

  • Network: Collection of devices (nodes) connected by communication links.
  • Point-to-Point
    • One dedicated link between exactly two devices; entire capacity reserved (e.g., serial cable between two routers).
  • Multipoint (Broadcast)
    • Two or more devices share a single link.
    • Spatial sharing – Multiple nodes transmit simultaneously via separate frequencies or codes.
    • Temporal sharing – Nodes take turns (time-division multiplexing).

Protocol-Level Communication Paradigms

  • Message Encoding → Transmission over Channel → Reception & possible retransmission modes.
  • Unicast: One-to-one.
  • Multicast: One-to-selected-many.
  • Broadcast: One-to-all.
  • Peer-to-Peer (P2P): Symmetric nodes acting both as client and server.
  • Client/Server: Dedicated server provides services to multiple clients.

Physical & Logical Topologies

  • Mesh
    • Every node directly connected to every other node.
    • Number of required links: \frac{n(n-1)}{2} for n devices.
    • Pros: high redundancy, robust, simple routing.
    • Cons: expensive cabling, complex I/O ports.
  • Star
    • All nodes attach to a central hub/switch.
    • Pros: easy to add/remove nodes; single cable fault isolates one node.
    • Cons: hub is single point of failure.
  • Bus
    • Single backbone cable with drop lines and taps.
    • Pros: inexpensive, easy to install.
    • Cons: difficult fault isolation; limited cable length and traffic.
  • Ring
    • Each node has exactly two neighbors; data travel in one logical direction.
    • Repeaters can regenerate signal; failures require bypass mechanisms.
  • Hybrid
    • Combination (e.g., star backbone interconnecting several bus segments) offers scalability and fault tolerance.

Essential Network Components

  • Nodes
    • End nodes: PCs, printers, IP cameras.
    • Intermediate nodes: hubs (legacy), switches, routers.
  • Media
    • Wired: copper, fiber, coax.
    • Wireless: IR, RF, microwave, satellite.
  • Services
    • Email, WWW browsing, cloud storage (Google Drive), file sharing, online gaming, instant messaging.

Wired Transmission Media

  • Ethernet Straight-Through Cable: Connect dissimilar devices (PC ↔ switch).
  • Ethernet Crossover Cable: Connect similar devices (switch ↔ switch, PC ↔ PC without hub).
  • Fiber-Optic Cable (FOC)
    • Immune to EMI, extremely high bandwidth, long distance.
  • Coaxial Cable – Legacy LANs, cable TV.
  • USB Cable – Short-range peripheral connectivity.

Wireless Media & Typical Use-Cases

  • Infrared (IR) – TV remotes, short-range line-of-sight links.
  • Radio Waves – Bluetooth, Wi-Fi (2.4 GHz / 5 GHz ISM bands).
  • Microwaves – Cellular backhaul, point-to-point links.
  • Satellite – GPS, global Internet backhaul, broadcast TV.

Classification of Computer Networks

  • LAN (Local Area Network)
    • Coverage: room → campus; wired Ethernet (hub/switch) or Wi-Fi.
  • MAN (Metropolitan Area Network)
    • Connects multiple LANs within a city (e.g., municipal fiber loop).
  • WAN (Wide Area Network)
    • Spans large geographic areas; relies on telecom carriers.
  • Internet
    • Public, global-scale WAN interconnecting heterogeneous networks.

Addressing in Computer Networks

IPv4 Address

  • Logical, location-dependent identifier.
  • 32-bit value represented as four octets in dotted-decimal form (e.g., 192.168.0.1).
  • Range 0.0.0.0 to 255.255.255.255.
  • Assigned manually (static) or dynamically (DHCP).

IPv6 Address (mentioned indirectly)

  • 128-bit logical address, represented in hexadecimal colon-separated notation; expansion beyond transcript scope.

MAC Address

  • Physical, hardware-burned identifier on NIC.
  • 48 bits, expressed in hexadecimal (e.g., 00!:!1A!:!2B!:!3C!:!4D!:!5E).
  • Globally unique; not tied to device location.

Port Number

  • 16-bit value 0!\text{–}!65535 identifying a process/service endpoint within a host.
  • Assigned and managed by OS; visible via tools such as resmon (Resource Monitor).

Conceptual & Practical Connections

  • Course maps directly to OSI/TCP-IP layered principles: physical media → protocols → addressing.
  • Real-time multimedia stresses timeliness & jitter, motivating QoS and congestion-control mechanisms (Modules 5 & 6).
  • Switching paradigms (Module 2) build on the physical/logical topologies introduced here.
  • Error detection (Module 3) ensures the accuracy characteristic, implementing CRC, Hamming, etc.
  • IPv4 subnetting (Module 4) refines the addressing concepts introduced (Classful vs. Classless).
  • Ethical & practical implication: ensuring global uniqueness of MAC addresses prevents identity collision; proper protocol adherence ensures interoperability between diverse vendors.