WEEK 5: Computer Networks

Networking

The process of delivering a message from a source to a destination.

Communication

The process of giving meaning to these messages received.

Computer Network

System of two or more computers linked together to share resources, exchange data, and communicate.

Computer Network

Key Features: 1. Connectivity: A bunch of computers linked together. 2. Cost-Efficient: Reduces expenses by sharing devices (e.g., printers, storage) and internet access. 3. Reliable: Provides backup and redundancy in case one device fails. 4. Communication Medium: Enables fast and efficient sharing of information through emails, messaging, file transfer, etc.

Uses of Network for People

Access to remote information, Person-to-person communication, Interactive entertainment

Communication Channel

A pathway over which information can be transferred.

How do Communication Channels Work

Source (Transmitter): The origin of the information. Channel: The medium/path through which data travels. Destination (Receiver): The end-point where the information is delivered.

Communication Channel

Ex. When you send a text message, your phone (transmitter) sends data through the cellular network channel, and your friend’s phone (receiver) gets it.

Types of Communication Transmission

Simplex Channel, Half-Duplex Channel, Full-Duplex Channel

Simplex Channel

Transmission is one-way only (unchanging direction). Ex: TV broadcast, radio broadcast.

Half-Duplex Channel

Transmission is two-way, but only one direction at a time; Requires “turn-taking” to switch sender and receiver roles. Ex: Walkie-talkie, CB radio.

Full-Duplex Channel

Transmission is two-way, simultaneous (both can send and receive at the same time). Ex: Telephone call, video conferencing.

Simplex Channel

Single-way

Half-Duplex Channel

Two-way but alternate

Full-Duplex Channel

Two-way simultaneous

Types of Transmission Technologies

Point-to-point Networks & Broadcast Networks

Point-to-point Networks

Network made up of direct connections between individual pairs of machines.

Point-to-point Networks

Communication occurs from one specific sender to one specific receiver. Ex: Telephone network, leased line connections.

Broadcast Networks

All machines on the network share one common communication channel.

Broadcast Networks

When a message is sent, every machine receives it, but only the intended recipient processes it. Ex: Traditional LAN with shared bus, Wi-Fi.

Point-to-point Networks

Private path (pair-to-pair communication).

Broadcast Networks

Shared path (one-to-all communication).

Types of Network Topologies

Bus Topology, Star Topology, Ring Topology, Tree Topology, Mesh Topology, Hybrid Networks, Daisy Chain

Bus Topology

All devices are connected to a single central cable (bus); Requires terminators at both ends to prevent signal reflection.

Bus Topology

Advantage: Easy to implement, cost-effective for small networks. Disadvantage: If the main cable fails, the whole network goes down.

Star Topology

Every device connects to a central hub/switch with point-to-point links; All communication passes through the central hub.

Star Topology

Advantage: Easy to manage, failure of one device does not affect others. Disadvantage: If the hub fails, the whole network stops.

Ring Topology

Devices form a circular path, with data traveling in one direction; Each device has a receiver and transmitter to pass data along.

Ring Topology

Advantage: Easy to install and expand, predictable data path. Disadvantage: Failure in one device or link can disrupt the entire network.

Tree (Hierarchical) Topology

Stars of stars: leaf/peripheral nodes connect to one parent only and don’t relay other traffic; The “central” control can be spread across multiple upper-level nodes instead of a single hub.

Tree (Hierarchical) Topology

Advantage: Scalable and easy to manage large networks. Disadvantage: Higher-level node failure affects all its sub-branches.

Mesh Topology

Devices are interconnected; data can travel on multiple paths.

Fully Connected Mesh

Usually too costly/complex and is used only for small node counts.

Fully Connected Mesh

Every node connects to all others (expensive, complex).

Partially Connected Mesh: Only some nodes are fully connected (practical use).

Practical Partial Meshes

__ meshes data takes the shortest path between nodes.

Mesh Topology

Advantage: Highly reliable, multiple paths ensure fault tolerance. Disadvantage: Costly and complex to install for large networks.

Hybrid Networks

Combination of two or more topologies (e.g., star + bus, star + ring) so the result doesn’t match any single standard type; Used in real-world networks where no single topology fits all needs.

Hybrid Networks

Advantage: Flexible and scalable. Disadvantage: Complex design and expensive.

Daisy Chain

Easiest way to add more computers (except in star networks) is to connect each in series and bounce messages along the line until the destination; It can take two forms: linear or ring.

Daisy Chain

Devices are connected in series (linear or ring form); Messages pass from one device to the next until reaching the destination.

Daisy Chain

Advantage: Simple and inexpensive. Disadvantage: Failure in one link can affect the whole chain.

Bus Topology

Ex: A small office with 5 computers connected to a single coaxial cable line. If one PC sends a file, the data travels across the same cable, and all other PCs can "see" it.

Star Topology

Ex: In a computer lab at school, each student’s PC is connected directly to a central switch or hub. If the teacher sends a file, it passes through the hub to reach the target student’s PC.

Ring Topology

Example: A bank’s branch network in the 90s, where each branch computer was connected in a circle. Data (like a transaction request) goes around the loop until it reaches the right computer.

Tree (Hierarchical) Topology

Example: A university network: 1. The main server connects to college-level switches. 2. Each college switch connects to multiple department switches. 3. Each department switch connects to computers in classrooms.

Mesh Topology

Example: The internet backbone between countries uses mesh topology. If one undersea cable fails, data can reroute through other cables connecting different regions.

Hybrid Networks

Example: A big mall’s Wi-Fi system: 1. Each floor uses a star topology (all routers connect to a floor switch). 2. The floor switches are connected using a bus or ring backbone.

Daisy Chain

Example: A series of holiday lights (Christmas lights). If one bulb (node) goes out in a linear daisy chain, all the lights after it stop working.

Bus Topology

One cable → like a clothesline with pegs.

Star Topology

Hub in middle → like a wheel with spokes.

Ring Topology

Circle → like a relay race track.

Tree (Hierarchy) Topology

Hierarchy → like a family tree.

Mesh Topology

All connected → like a spider web.

Hybrid Network

Mixed of types → like a smoothie of topologies.

Daisy Chain

Linked in series → like holiday lights.

Distributed System

CDP (Centralized Data Processing), DDP (Distributed Data Processing), Client/Server

CDP (Centralized Data Processing)

Ex: In the 1970s mainframe systems, a bank had one big central computer that processed all customer transactions while terminals (screens/keyboards) only served as input/output devices.

CDP (Centralized Data Processing)

The conventional way of doing all the processing and control on centralized computers.

DDP (Distributed Data Processing)

Manipulation of data using distributed systems; Data is processed across multiple interconnected computers, each handling part of the workload.

DDP (Distributed Data Processing)

Ex: In a university network, the registrar’s office server manages enrollment, the accounting server handles payments, and the library server manages borrowing records—working together but independently.

Client/Server

Extension of distributed data processing, it provides the best of both centralized & distributed data processing.

Client/Server

Example: When you use Gmail: Your device/browser

Client/Server

Special form of distributed processing where the server provides resources/services and the client requests them.

CDP (Centralized Data Processing)

One restaurant kitchen cooks everything for all customers.

DDP (Distributed Data Processing)

Each food stall in a food court handles its own specialty.

Client/Server

You (client) order food, the chef (server) prepares and gives it to you.

Types of Network

LAN (Local Area Network), MAN (Metropolitan Area Network), WAN (Wide Area Network), PAN (Personal Area Network)

LAN (Local Area Network)

Connects devices over short distances, usually owned by one person or organization. 10–100 Mbps (can be higher today).

LAN (Local Area Network)

What Network is this? Example: A school computer lab where all PCs are connected to the same Wi-Fi or Ethernet network.

MAN (Metropolitan Area Network)

Covers a city or large campus, bigger than a LAN but smaller than a WAN. ~5–10 Mbps (older standard; now can be higher with fiber).

MAN (Metropolitan Area Network)

What Network is this? Example: A city government network connecting multiple offices (e.g., City Hall, Police HQ, Fire Department)

WAN (Wide Area Network)

-Spans large physical distance (geographically dispersed collections of LANs)

WAN (Wide Area Network)

Not owned by any one organization, but rather exists under collective or distributed ownership and management. 256Kbps-2Mbps (classic rates; modern WANs are faster with broadband/fiber).

WAN (Wide Area Network)

What Network is this? Example: The Internet is the biggest WAN, linking networks across the globe.

PAN (Personal Area Network)

Very small network around one person, usually within 10 meters.

PAN (Personal Area Network)

Personal computer devices that are used to develop the personal area network are: Laptop, Mobile phones, Media player, and PlayStation.

PAN (Personal Area Network)

What Network is this? Example: Connecting your phone to wireless earbuds via Bluetooth or laptop hotspot to your phone.

PAN (Personal Area Network)

Your personal bubble (Bluetooth, hotspot, gadgets).

LAN (Local Area Network)

Your house, school, or office Wi-Fi.

MAN (Metropolitan Area Network)

Your entire city’s network (e.g., LGU offices).

WAN (Wide Area Network)

The whole world (Internet).

Network Devices

Modem, Router, Switch, Access Point/Mesh Node, Firewall

Modem

Connects your home/school to the ISP (turns wall signal into internet). Ex: The box your internet provider installs that plugs into the wall and brings internet into your home.

Router

Shares the connection, gives devices IP addresses, and creates your Wi-Fi name.

Switch

Provides extra wired connections for more computers, printers, or servers. Ex: In a computer lab, the switch connects 20 PCs to the same network.

Access Point/Mesh Node

Extends or creates Wi-Fi coverage in different rooms or areas. Ex: A Wi-Fi extender placed upstairs to boost the Wi-Fi signal from your router.

Firewall (often inside the router)

Protects your network by filtering harmful or unauthorized traffic. Often built into modern routers. Ex: Stops hackers or malware from entering your home/school network.

Network Cables

Ethernet (UTP Cat5e/Cat6/Cat6a, RJ-45), Fiber (SM/MM; LC/SC), Coaxial, Telephone (RJ-11/DSL)

Ethernet (UTP Cat5e/Cat6/Cat6a, RJ-45)

Everyday wired links; Stable & Fast (use Cat6 as a safe default).

Ethernet (UTP Cat5e / Cat6 / Cat6a, RJ-45)

Most common cable for wired internet. Uses an RJ-45 connector; Speed/Use: Cat5e (1 Gbps), Cat6 (1–10 Gbps, safer default), Cat6a (better shielding, longer runs). Ex: Blue/gray cable connecting your PC/console to the router.

Fiber (SM/MM; LC/SC)

Very high speed & long distance; Building/backbone links.

Fiber (SM/MM; LC/SC)

Uses light instead of electricity to transmit data. Extremely fast and good for long distances. Speed/Use: 1–100+ Gbps, often used in backbone links between buildings, campuses, or ISPs. Ex: Thin yellow (SM)/orange (MM) fiber cables in data centers.

Coaxial

Cable-internet line between wall and modem.

Coaxial

Thick cable with a copper core, mostly used for TV and internet service. Speed/Use: Connects the wall outlet → cable modem (e.g., Comcast, Sky, PLDT cable internet). Ex: Round black cable that screws into the back of your modem.

Telephone (RJ-11/DSL)

Used by DSL lines from wall to modem.

Telephone (RJ-11/DSL)

Older twisted-pair cable with RJ-11 connector, smaller than Ethernet. Speed/Use: Used for DSL internet (internet over telephone lines). Ex: Thin gray cable from your telephone wall jack → DSL modem.