CMS 703 · RSU 2024/2025
Data Communication
& Networks
Complete Exam Cheat Sheet
the lecturer · Rivers State University
5 Components
Fourier Series & Transform
OSI 7 Layers
Network Topologies
Switching & Routing
Lecturerthe lecturer
InstitutionRivers State University
Course CodeCMS 703
Session2024 / 2025
Section 1
Data Communication
The sharing/transfer of information locally or remotely between two or more devices using computing and communication technologies.
3 Fundamental Principles
Section 1 · Most Tested
5 Components of a
Data Communication System
Without a protocol: two devices may be connected but not communicating · like a French speaker talking to a Japanese-only speaker.
Section 2
Data Representation
All data = bit patterns (0s and 1s)
Type How Represented Key Detail
Text Bit patterns (codes) Unicode = 32 bits/char (all languages). ASCII = Basic Latin (127 chars), subset of Unicode
Numbers Direct binary NOT via ASCII · converted directly to binary; includes bits for math operations
Images Matrix of pixels Pixel bit patterns. Colour = RGB or YCM. Black=00, D.Grey=01, L.Grey=10, White=11
Audio Continuous signal → digital Sampled → Quantized → Encoded to bit patterns
Video Images + signal processing Continuous entity OR combination of images. Must be Sampled → Quantized → Encoded
Key chain: Continuous Signal → Sample (measure at intervals) → Quantize (approximate finite values) → Encode (represent as bits)
Section 3
Data Flow · 3 Transmission Modes
Defines the direction of data transmission between devices
→
Simplex
One direction only. Sender can only send; receiver can only receive.
Keyboard→Computer · TV Broadcast · Radio · Computer→Printer · Monitor (output only)
⇄
Half-Duplex
Both directions, but NOT simultaneously. One at a time; like a one-lane road with construction.
Walkie-talkie (say "over") · WiFi · CB Radio · USB v2 · Ethernet Hubs · Web Browser
⇌
Full Duplex
Both directions simultaneously. Channel capacity is shared between both directions.
Telephone Network · Live Chat · Router+Switch · Duplex Fibre-Optic · USB v3
Section 4 · Guided Media
Transmission Media · Guided
Cable directs signals along a specific path (also called bound media)
Type 1
Twisted Pair
Two copper conductors twisted together, each insulated with plastic. Number of twists per unit = quality.
STP (Shielded) · foil + copper shielding; less interference; more secure

UTP (Unshielded) · flexible; susceptible to interference; up to 1 km
Uses: Telephone, 10Base-T, 100Base-T LAN
Type 2
Coaxial Cable
Central copper core → insulator → outer conductor foil → plastic cover.
Layers (inside → outside):
Central Core → Insulator → Outer Conductor → Plastic Cover

Outer conductor = noise shield AND circuit conductor
Uses: Cable TV, CCTV, Satellite install, Telephone networks
Both can be used for longer distances than twisted pair. Coaxial supports more stations on a common line.
Section 4 · Guided Media · High Exam Weight
Fibre-Optic Cable
How it works
Transmits signal as light. Made of glass or plastic. Uses reflection to guide light · beam moving through core reflects off cladding due to density difference.

Layers (outside → inside):
Outer Jacket (PVC/Teflon) → Kevlar → Cladding → Core
Uses: Internet backbone, 100Base-FX, 1000Base-X, undersea cables, medical laser surgery
6 Advantages
  • High bandwidth
  • Low attenuation (8–50 km vs 5 km for copper)
  • Immune to EM interference
  • Resistant to corrosion (glass)
  • Lightweight
  • Immune to tapping
3 Disadvantages
  • Requires expert installation
  • Expensive to install
  • Fragile · breaks if bent sharply
Section 4 · Unguided Media
Wireless Communication
Signal travels in 3 ways: Ground · Sky · Line-of-Sight
Radio
3 KHz – 1 GHz · Omnidirectional · Long range (sky mode) · Multicasting
Microwave
1 – 300 GHz · Unidirectional · Line-of-sight · Parabolic dish / Horn antenna
Infrared
300 GHz – 400 THz · Cannot penetrate walls · Short range only
MediumDirectionKey Examples
Radio Waves Omni AM/FM radio, TV, Maritime, Cordless mics, Paging
Microwave Uni Terrestrial: short wireless; Satellite: TV, telephony, live news. Repeaters every 25–30 km
Infrared Short Remote controls, Night vision, Missile guidance, Thermal cameras, Gas detectors
Microwave key rules: Antennas MUST be aligned. Very high frequency cannot pass through walls. Some bands require regulatory permission.
Section 5 · Fourier Analysis
Fourier Analysis
Decomposes complex signals → simple sine & cosine waves.
Converts data from Time Domain → Frequency Domain.
Created by Joseph Fourier (French mathematician & physicist).
Fourier Series
For Periodic Signals
Signals that repeat from −∞ to +∞. Expands signal into harmonics (sin/cos with different amplitudes and frequencies).
Fourier Transform
For Non-Periodic Signals
Real-life signals are generally non-periodic. Decomposes into oscillatory functions. No information created or lost.
4 Application Areas
Engineering
Filter noise, compress signals, data analysis
Physics
Acoustics, optics, quantum mechanics
Neuroscience
Find hidden rhythms in neural recordings
Mathematics
Reduce complex differential equations to algebraic
Section 6 · Fourier Series
Fourier Series Formula
f(x) = a₀/2 + Σ [ aₙ cos(nπx/L) + bₙ sin(nπx/L) ]
Where n = 1 to ∞ and L = period of the signal
Coeff.FormulaMeaning
a₀ (1/2L) ∫ f(x) dx Average (DC) value of the signal
aₙ (1/L) ∫ f(x)·cos(nπx/L) dx Cosine coefficients
bₙ (1/L) ∫ f(x)·sin(nπx/L) dx Sine coefficients
Even Function
bₙ = 0
f(−x) = f(x)
→ Fourier Cosine Series
Odd Function
aₙ = 0
f(−x) = −f(x)
→ Fourier Sine Series
Section 6 · Fourier Series
Period · Frequency · Amplitude
Period (T)
Distance before repeat
sin(x) → 2π
sin(nx) → 2π/n

Larger n = shorter period

sin(2x) = π
sin(3x) = 2π/3
sin(5x) = 2π/5
Frequency (f)
Opposite of Period
f = 1/T

sin(x) → Fundamental Frequency

sin(3x), sin(5x), sin(7x)... → Harmonics (integer multiples of fundamental)
Amplitude (A)
Height of Wave
Controls the size of the wave.

y = A·sin(θ)

If A = 1 → wave moves from +1 to −1
Square wave approximation:
f(x) = (4/π) [ sin(x)/1 + sin(3x)/3 + sin(5x)/5 + sin(7x)/7 + … ]
3 Types of Fourier Series Expansion: (1) Trigonometric · (2) Complex Exponential · (3) Polar / Harmonic
Section 6 · Very High Exam Weight
Square Wave · Full Derivation
Given: f(x) = A for 0 < x < π  |  f(x) = −A for π < x < 2π
StepResultWhy?
Find a₀ a₀ = 0 Symmetric wave · positive and negative areas cancel: Aπ − Aπ = 0
Find aₙ aₙ = 0 sin(nπ) = 0 and sin(0) = 0 for all integer n · everything cancels
Find bₙ (even n) bₙ = 0 (−1)ⁿ = +1 when n is even → 1 − 1 = 0
Find bₙ (odd n) bₙ = 4A/nπ (−1)ⁿ = −1 when n is odd → 1 − (−1) = 2 → bₙ = A/nπ × 2 × 2 = 4A/nπ
f(x) = (4A/π) [ sin(x) + sin(3x)/3 + sin(5x)/5 + sin(7x)/7 + … ]
KEY CONCLUSION: Only ODD harmonics survive. Even harmonics cancel out.
Section 7 · Fourier Transform
Fourier Transform
For non-periodic signals · no information created or lost
F(ω) = ∫ f(t) · e⁻ⁱωᵗ dt
Forward Transform (time → frequency)
f(t) = (1/2π) ∫ F(ω) · eⁱωᵗ dω
Inverse Transform (frequency → time)
Note: e⁻ⁱωᵗ = cos(ωt) − i·sin(ωt)  |  f(t) = time domain  |  F(ω) = frequency domain
Worked Example (Exam Answer)
Find F(ω) of f(t) = e⁻ᵃᵗ·u(t), a > 0 where u(t)=1 for t≥0, u(t)=0 for t<0

F(ω) = ∫₀^∞ e⁻ᵃᵗ · e⁻ⁱωᵗ dt = ∫₀^∞ e⁻⁽ᵃ⁺ⁱω⁾ᵗ dt

Using ∫₀^∞ e⁻ᵇᵗ dt = 1/b (where b = a+iω, a > 0):
F(ω) = 1 / (a + iω)
Square pulse: F(ω) = T·sinc(ωT/2). Wider pulse in time → narrower frequency spread. Narrower pulse → wider spread.
Section 9
Serial vs Parallel Transmission
Serial Transmission
Bits: One at a time
Wires: 1 channel
Distance: Long distance
Cost: Cheaper
Speed: Slower (short dist.)
Risk: Sync issues
USB · Ethernet · RS-232 · Satellite · WiFi · 4G/5G · Fibre backbone
Parallel Transmission
Bits: Multiple at once
Wires: Multiple (1 per bit)
Distance: Short distance only
Cost: Expensive
Speed: Faster
Risk: Signal skew
CPU data bus · Computer printer port · Internal memory transfer
Long-Distance Serial Examples
TechnologyDetail
Digital TelephonyVoice sent bit by bit over T1/E1 lines
Fibre-Optic InternetLight pulses in single stream · backbone & undersea cables
WiFi / 4G / 5GData packets transmitted bit by bit over radio waves
Section 10
Asynchronous vs Synchronous
Asynchronous
| Start | D0 D1 D2 D3 D4 D5 D6 D7 | Parity | Stop |
Unit: Character by character
Clock: No shared clock
Overhead: Start + Stop bits
Error: Parity bit
Best for: Sporadic data
RS-232 · Keyboard · Mouse · Dial-up modem
Real-life: Short text messages
Synchronous
| Sync | Sync | Data | Data | Data | Data | Data |
Unit: Blocks / Frames
Clock: Shared clock / preamble
Overhead: None (no start/stop)
Error: Checksum / CRC
Best for: Bulk continuous data
Ethernet · Broadband · Digital Telephony
Real-life: Phone calls, Video calls
Async Advantages
  • Simple & cost-effective
  • Good for sporadic data
  • Easy to implement
Async Disadvantages
  • Extra bits reduce efficiency
  • Slower for bulk data
  • Less precise timing
Section 11
Computer Networks
A collection of interconnected devices that communicate and share resources
LAN
Local Area Network
Office/Home
High speed, small area, inexpensive
MAN
Metropolitan Area Network
City / Large Campus
Connects nearby LANs
WAN
Wide Area Network
Global / Country
Connects LANs + MANs; Internet
LAN properties: Very high speed · Small geographical area · Less expensive technology · Share hardware/software · Send messages & emails between users
Section 11 · Network Topologies
Network Topologies
Connection arrangement of nodes · defines cable, computer & peripheral configuration
Bus Topology
Single Backbone Cable
Advantages
  • Easy to add nodes
  • Less cable than star
  • Cheaper; good for small networks
Disadvantages
  • Main cable break = whole network down
  • Needs terminators at both ends
  • Low security; not for heavy traffic
Star Topology · Most Common
Central Hub/Switch
Advantages
  • Easy install & wiring
  • One node fail = others unaffected
  • Easy fault detection; easy add/remove
Disadvantages
  • Requires large cable length
  • Hub failure = entire network down
Ring Topology
Closed Loop Circle
Advantages
  • No central device needed
  • Equal access; easy install
  • Easy fault detection
Disadvantages
  • Sequential = delays
  • Single break = whole network disrupted
Mesh Topology
Every Node Connected
Advantages
  • Simultaneous multi-device data
  • Node failure = network unaffected
Disadvantages
  • Very expensive; high redundancy
  • Setup & maintenance very difficult
Section 12 · Extremely Common Exam Topic
OSI Model · 7 Layers
Open Systems Interconnection · Released 1984 by ISO
7 Application User interface; file, print, email, database services; user access to network
6 Presentation Syntax & grammar; data format, encryption and compression; translates between formats
5 Session Manages sessions/dialogues; inserts checkpoints; resumes interrupted dialogues; security parameters
4 Transport End-to-end delivery; divides into packets; resequences at destination; flow & error control
3 Network Routing; translates logical → physical addresses; manages traffic, switching, congestion
2 Data Link Assembles into frames; converts frames↔bits; physical addressing; error/flow/access control · single link
1 Physical Bit stream over physical medium; electrical/mechanical/timing specs; data rate, synchronization; hardware-specific
Top-Down Mnemonic:
All People Seem To Need Data Processing
Bottom-Up Mnemonic:
Please Do Not Throw Sausage Pizza Away
Section 13 & 14
Switching & Routing
Circuit Switching
Dedicated Circuit
Physical path exclusively reserved for one connection for its entire duration. Released after transfer.

Example: Public Telephone Network (PTCL)
  • Efficient, fewer errors, reliable
  • Bandwidth wasted (e.g. when listening)
  • Complex setup; slow circuit establishment
Packet Switching
Data in Packets
Data split into packets with headers (routing info). Packets independent, can take different paths. Path shared among users. Connectionless.

Example: The Internet
  • Efficient resource use; handles variable rates
  • Packet reordering takes time
  • Not good for small data packages
Source Routing
Source node specifies entire route before transmission. Used to troubleshoot and improve performance.
Hop-by-Hop Routing
Source does NOT know full path. Each node passes packet to next node only. Based on channel availability.
Section 15 & 16
Protocols · Analog/Digital · NIC
Protocol
A set of rules and procedures governing communication. Without it, connected devices cannot communicate.

Functions: Defines packet size · Numbering scheme · Error/flow control · Connection setup/termination · Data security · Routing algorithms · Communication logs
Analog vs Digital
Analog: Continuous waveform (e.g. human voice)

Digital: Discrete ON/OFF states (0 or 1)

Digital→Analog for transmission (modulation), converted back at receiver

Bandwidth = data transfer rate = bits per second (bps)
Network Interface Card (NIC)
Hardware device that physically connects computer to network cable. Installed in expansion slot. Provides port for cable.

Functions: Send data to host · Receive & translate incoming data to machine language · Prepare data from computer for network cable · Control data flow
Exam Strategy
Top 15 Exam Tips
1
5 Components · Know each definition + example. She defines them precisely.
2
3 Principles (Delivery, Accuracy, Timeliness) · Easy 3-mark question.
3
Data Flow · WiFi = half-duplex. Telephone = full duplex. Always include examples.
4
Fibre-Optic · Know all 6 advantages + 3 disadvantages by heart.
5
Square Wave derivation · Know why a₀=0, aₙ=0, bₙ=4A/nπ (odd only).
6
Even/Odd functions · Even→Cosine Series; Odd→Sine Series.
7
Period formula · sin(nx) = 2π/n. Calculate for any n instantly.
8
F.T. worked example · e⁻ᵃᵗu(t) → 1/(a+iω). Know every step.
9
Time-Frequency · Wider pulse = narrower spectrum. Narrower = wider.
10
Serial vs Parallel · Serial = long distance. Parallel = short/internal.
11
Async vs Sync · Know frame structures + error detection methods.
12
OSI Model · All 7 layers, order, and functions. Both directions.
13
Topologies · All 4: advantages + disadvantages (Bus, Star, Ring, Mesh).
14
Circuit vs Packet · Dedicated path vs shared path. PTCL vs Internet.
15
OFDM = Orthogonal Frequency Division Multiplexing → 5G & LTE. Fourier in real life.
Quick Reference
Master Reference Tables
Transmission Media
MediaTypeDirectionFrequencyKey Use
Twisted PairGuidedBoth-LAN, Telephone
CoaxialGuidedBoth-Cable TV, CCTV
Fibre-OpticGuidedBoth-Internet Backbone
Radio WavesUnguidedOmni3KHz–1GHzBroadcasting
MicrowaveUnguidedUni1–300GHzLong distance, Satellite
InfraredUnguidedShort300GHz–400THzRemote controls
OSI Layers · One-Word Recall
7
Application
User
6
Presentation
Format
5
Session
Dialogue
4
Transport
Packets
3
Network
Routing
2
Data Link
Frames
1
Physical
Bits