Fundamentals of Computer Networks – Lesson 1 Notes

Lesson Outline

• Brief History of Computer Networks
• Computer Networking (definition & map analogy)
• Elements of Communication
• Components of a Network
• Network Topologies
• Types of Network Infrastructures
• Network Devices

Brief History of Computer Networks

• ARPANET (Advanced Research Projects Agency Network)

  • Sponsored by U.S. DoD’s ARPA (now DARPA).

  • Pioneered inter-networking of heterogeneous computers.

• Initial 4 nodes (1969):

  • University of California-Los Angeles (UCLA)

  • Stanford Research Institute (SRI)

  • University of California-Santa Barbara (UCSB)

  • University of Utah

• First hardware installed: $\text{2 Sep 1969}$ at UCLA.

• “Birthdate” of ARPANET: first message on $\text{29 Oct 1969}$.

  • Attempted login “LOG”; only “L” “O” transmitted $\rightarrow$ crash; success a few hours later.

  • Distance spanned: $352\;\text{mi}=566\;\text{km}$.

• Key figures: Prof. Leonard Kleinrock (lead); graduate student Vint Cerf.

  • Cerf + Bob Kahn later created $TCP/IP$.

• Philippine milestone

  • $\text{29 Mar 1994, 01{:}15\,AM}$ — Engr. Benjamin “Benjie” Tan (PLDT) established the first PH Internet link via Cisco 7000 router.

  • 64 Kbps serial link $\left(64\,\text{Kbps}\right)$ through SprintLink → NASA Ames Research Center.

  • Usenet post on soc.culture.filipino announced: “FINALLY connected …” (two-day delay due to technical issues).

  • Suggested reading: https://jimayson.wordpress.com/2011/08/13/the-night-benjie-hooked-up-the-philippines-to-the-internet/

Computer Networking – What is a Network?

• Analogy: subway / MRT maps illustrate interconnected routes & nodes.

• Definition

  • Collection of computers capable of transmitting, receiving, exchanging voice, data, video.

  • Enables automation, self-management, resource sharing.

• Connection media: cables, telephone lines, radio waves, satellites, infrared beams.

• Minimum of two computers linked for resource/file sharing or electronic communication.

Elements of Communication

1. Message Source (Sender)

2. Channel (Transmission Medium)

3. Message Destination (Receiver)

• Any communication—human or computer—requires these three.

Components of a Network

• Infrastructure categories: Devices, Media, Services.

Devices

End Devices

• Interface between users & the network.

• Examples:

  • Computers (workstations, laptops, file & web servers)

  • Network printers

  • VoIP phones

  • TelePresence endpoints

  • Security cameras

  • Mobile/handheld (smartphones, tablets, PDAs, wireless POS or barcode readers)

• “Host” = source or destination of a transmitted message.

Intermediary Devices

• Interconnect end devices or multiple networks.

• Classes

  • Network Access: switches, wireless access points (WAPs)

  • Internetworking: routers

  • Security: firewalls

Media

• Provide the physical channel for messages.

• Three modern types:

  1. Metallic wires (copper) – data encoded as electric impulses.

  2. Fiber optic – pulses of light (infrared or visible).

  3. Wireless – electromagnetic waves encode bits.

Network Topologies

Diagram Types

• Physical topology: real-world device/port/cable layout.

• Logical topology: devices, ports, IP addressing relationships.

Star Topology

• All communication passes through a central switch (concentrator).

• Failure impact: switch failure ⇒ total outage; single-cable failure ⇒ one host down.

Extended Star

• Star with additional switch(es) cascading from main center.

• Central failure disconnects entire network, yet individual stars maintain internal communication.

Full Mesh

• Every device links to every other device.

• Pros: full redundancy; alternative paths on link failure.

• Cons: expensive—multiple links & interfaces.

Partial Mesh

• Balance cost vs redundancy.

• Example: LA & NY fully connected; SF, Detroit, Miami route traffic via LA/NY.

Hub-and-Spoke

• One hub (central) with multiple spokes.

• Example: HQ in New York (hub) with branches in Miami & LA (spokes).

• Traffic between spokes usually forced through hub for security inspections.

Hybrid

• Mixture of several topologies.

• Example scenario:

  • New York campus LAN: two buildings → access/distribution (partial-mesh) & core (full-mesh).

  • Buildings connected with full mesh to core switches.

  • WAN: full mesh between NY–LA–Miami; hub-and-spoke between NY (hub) and Amsterdam/Paris (spokes).

Types of Network Infrastructures

PAN (Personal Area Network)

• Around one person; devices: smartphones, wearables, tablets, laptops.

• Range ≈ $\le 10\,\text{m}$.

LAN (Local Area Network)

• Limited area: home, school, building, campus.

• Media: copper & fiber; high speed.

• Single org/individual administration; network-level security & access control.

MAN (Metropolitan Area Network)

• Spans bigger than LAN but smaller than WAN (e.g., a city).

• Often single entity operation.

• Mostly fiber; wireless possible.

• Costly; needs skilled engineers.

WAN (Wide Area Network)

• Largest scale: interconnects LANs/MANs across cities, states, countries, continents.

• Usually managed by TSPs/ISPs.

• High build & maintenance cost; complex management.

Other Notable Types

• WLAN (Wireless LAN): small area wireless connectivity (homes, offices, cafés).

• SAN (Storage Area Network): high-speed dedicated network for pooled storage & multiple servers.

• CAN (Campus Area Network): connects multiple buildings/departments on a single site.

• VPN (Virtual Private Network): private overlay using public Internet for secure remote connectivity.

• VLAN (Virtual LAN): logical segmentation of a switched network into separate broadcast domains for security & efficiency.

Network Devices

• Two overarching roles:

  1. Establishing a connection (e.g., router, modem).

  2. Maintaining, protecting, enhancing that connection (e.g., hub, switch, firewall, repeater, gateway).

• General purposes

  • Facilitate data transmission & communication.

  • Provide efficient, secure connectivity.

  • Optimize traffic flow & performance.

  • Enforce access control & threat prevention.

  • Simplify management/configuration.

  • Extend coverage; overcome signal limits.

Major Manufacturers (illustrative list)

Cisco • Juniper Networks • Huawei • Extreme Networks • TP-Link • Linksys • Netgear • D-Link • ASUS • Belkin • Edimax • Teltonika

Switch

• Multi-port device improving efficiency; reads MAC addresses.

• Connects LAN segments.

• Types:

  • Modular: expandable ports/modules.

  • Fixed-configuration: set port count, cheaper.

• Managed vs Unmanaged

  • Managed: admin control over VLANs, QoS, traffic, security.

  • Unmanaged: plug-and-play basic connectivity.

Router

• Directs traffic by computing best paths across networks/topologies.

• Stores info about connected networks; often includes ACL-based packet filtering.

• Border router: LAN ↔ WAN edge.

• First line of defense—configure to allow only authorized traffic.

• Key internal components: CPU, RAM/Flash, interfaces (WAN/LAN), power supply.

Firewall

• Monitors & filters traffic per security policies.

• Uses whitelists (allowed) and/or blacklists (denied).

• Deployed at network perimeter or between internal segments (e.g., sales vs IT).

• Critical when handling sensitive info.

Modem (Modulator-Demodulator)

• Converts digital ↔ analog signals to traverse different media.

• Serial interface: RS-232.

• Variants:

  1. DSL modem – telephone lines; slowest.

  2. Cable modem – TV coax; faster.

  3. Wireless modem – RF/Cellular link to ISP; fastest.

Wireless Access Point (WAP)

• Transceiver creating a WLAN; bridges wireless clients to wired Ethernet.

• Larger areas may need multiple WAPs for full coverage.

• SSID identifies the WLAN; clients must match SSID for authentication.

Ethical, Philosophical & Practical Implications

• Data privacy compliance (RA 10173) underscores the ethical duty to secure personal information in any networked environment.

• Redundancy vs cost (full-mesh vs partial) reflects a classic engineering trade-off between reliability and budget constraints.

• Security layers (router ACLs, firewalls, VLANs, VPNs) illustrate the principle of defense-in-depth—essential as automation increases and cyber-threats evolve.

• Historical milestones (ARPANET, PH first link) highlight how collaborative research & infrastructure investment drive societal connectivity.

Numerical & Technical References (Quick List)

• First ARPANET message distance: $566\,\text{km}$.

• Four original ARPANET nodes (UCLA, SRI, UCSB, Utah).

• Philippine first Internet bandwidth: $64\,\text{Kbps}$ serial link.

• PAN radius ≈ $10\,\text{m}$.