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📡 Data Communication Course

ការទំនាក់ទំនង
ទិន្នន័យ

Data Communication គឺជាការបញ្ជូន និងទទួលទិន្នន័យ (Data) រវាងឧបករណ៍ ឬប្រព័ន្ធ ២ ឬ ច្រើន ដោយប្រើ Medium (ខ្សែ/ខ្យល់) — គ្របដណ្ដប់ Signals, Protocols, Network Layers, Security, Wireless, 5G Network ។

15
មេរៀន
3
កម្រឹត
7
OSI Layers
100%
ភាសាខ្មែរ
🟢 Basic (ចាប់ផ្ដើម)
  • Data Communication គឺជាអ្វី
  • Signal Analog vs Digital
  • Transmission Media (Wired/Wireless)
  • Digital Encoding Techniques
  • Multiplexing (TDM/FDM/WDM)
🟠 Intermediate (មធ្យម)
  • Data Link Layer, MAC Address
  • Network Layer, IP Address, Routing
  • Transport Layer, TCP vs UDP
  • Wireless Technology, WiFi Standards
🔴 Advanced (ខ្ពស់)
  • OSI Model 7 Layers & TCP/IP
  • Network Security, Encryption
  • Protocol Suite (HTTP/HTTPS/FTP/DNS)
  • Error Detection (CRC, Hamming)
  • Internet, Cloud, SDN
  • 5G, IoT, Future Networks
💡 ការអនុវត្ត
  • Packet Tracer / Wireshark
  • Network Simulation Tools
  • Real-world Protocol Analysis
  • IP Addressing & Subnetting
🟢 Basic — មេរៀនទី ១

ការណែនាំ
Data Communication

ស្វែងយល់ពី Data Communication គឺជាអ្វី, គ្រប់ Component, Direction, Bandwidth, Throughput, Latency ។

Data Communication គឺជាអ្វី?

Data Communication គឺជាដំណើរការផ្ញើ (Transmit) និងទទួល (Receive) ទិន្នន័យ (Data) ពី Source ទៅ Destination ដោយប្រើ Transmission Medium ។

📤 Sender
Source
→
💻 Encoder
Transmitter
→
〰️ Medium
Channel
→
💻 Decoder
Receiver
→
📥 Receiver
Destination
Component ទាំង ៥
  • Message — ព័ត៌មាន/ទិន្នន័យ (text, image, video, audio)
  • Sender — ឧបករណ៍ផ្ញើ (computer, phone)
  • Receiver — ឧបករណ៍ទទួល
  • Medium — ច្រកបញ្ជូន (cable, wifi)
  • Protocol — ច្បាប់ / Rule (TCP/IP)
Data Flow Direction
Simplex

ផ្ញើបានតែ ទិសតែមួយ ។ ឧ: Keyboard → Computer, TV Broadcast

Half-Duplex

ផ្ញើម្ខាងម្ដង, មិនអាចស្ដាប់ + និយាយ ក្នុងពេលតែមួយ ។ ឧ: Walkie-Talkie

Full-Duplex

ផ្ញើទាំងពីរទិសក្នុងពេលតែមួយ ។ ឧ: Phone Call, Chat

Bandwidth, Throughput & Latency
ពាក្យនិយមន័យឯកតាឧទាហរណ៍
Bandwidthចំនួន Data អតិបរមា ដែលបញ្ជូនបាន/វិនាទីbps, Kbps, Mbps, Gbps100 Mbps Connection
Throughputចំនួន Data ដែលបញ្ជូនបានពិតប្រាកដbpsទូទៅ < Bandwidth
Latencyពេលវេលារង់ចាំ (Delay) ក្នុងការបញ្ជូនms (milliseconds)Ping 20ms
Jitterការប្រែប្រួលនៃ LatencymsVideo call quality
BERBit Error Rate — កំហុស bits ក្នុង 1 secondratio10⁻⁶
Nyquist Theorem (Noiseless)
Max Data Rate = 2 × Bandwidth × log₂(L)
L = number of signal levels, Bandwidth in Hz
Shannon's Theorem (Noisy Channel)
Max Data Rate = Bandwidth × log₂(1 + SNR)
SNR = Signal-to-Noise Ratio
🟢 Basic — មេរៀនទី ២

សញ្ញាន (Signals)

Analog Signal, Digital Signal, Periodic/Aperiodic, Frequency, Amplitude, Phase, Modulation Techniques ។

Analog Signal

Analog Signal ជា Signal ដែលមានតម្លៃ ប្រែប្រួលជាបន្ដបន្ទាប់ (Continuous) — ដូចជា Wave ។

Analog Signal (Sine Wave)
Amplitude t
  • Amplitude (A) — កម្ពស់ Wave
  • Frequency (f) — Hz — ចំនួនវដ្ដ/វិនាទី
  • Period (T) — T = 1/f
  • Phase (φ) — ទីតាំងចាប់ផ្ដើម Wave
Digital Signal

Digital Signal ជា Signal ដែលមានតម្លៃ ថេរ 2 ប្រភេទ — High (1) ឬ Low (0) ។

Digital Signal (Square Wave)
HIGH (1) LOW (0) t
  • Bit Rate — bps (bits per second)
  • Bit Length — ចម្ងាយ 1 bit ក្នុង Medium
  • 0 / 1 — ច្បាស់លាស់, ងាយ Error Correct
  • ប្រើក្នុង Computer Networks
Modulation — ការបំប្លែង Signal

Modulation គឺការបំប្លែង Digital → Analog ដើម្បីបញ្ជូនតាម Analog Channel (ឧ: Telephone, Radio) ។

Modulationការបំប្លែងការប្រើប្រាស់
ASK — Amplitude Shift Keyingប្ដូរ Amplitude (0=Low, 1=High)Optical Fiber
FSK — Frequency Shift Keyingប្ដូរ Frequency (0=f₁, 1=f₂)Radio, Modem
PSK — Phase Shift Keyingប្ដូរ Phase (0=0°, 1=180°)WiFi, Satellite
QAM — Quadrature Amplitude Modប្ដូរ Amplitude + PhaseCable Modem, LTE
💡

QAM-64 ប្រើ 64 Signal States → ផ្ញើបាន 6 bits ក្នុង 1 Symbol ។ ប្រើក្នុង 4G LTE, Cable TV ។

🟢 Basic — មេរៀនទី ៣

Transmission Media

Wired Media (Twisted Pair, Coaxial, Fiber Optic) និង Wireless Media (Radio, Microwave, Infrared, Satellite) ។

Wired (Guided) Media
ប្រភេទBandwidthចម្ងាយការប្រើប្រាស់គុណសម្បត្តិ
Twisted Pair (UTP/STP) Cat5e: 1 Gbps
Cat6: 10 Gbps		 100 m LAN, Telephone, DSL ថោក, ងាយដំឡើង
Coaxial Cable Up to 10 Gbps 500 m – km Cable TV, Internet Noise ទាប
Fiber Optic Tbps+ 100+ km WAN, Backbone, Internet លឿន, ចម្ងាយឆ្ងាយ, មិន Interfere
🔌 UTP Cable

Unshielded Twisted Pair — ខ្សែ Copper ២ ចំណូលប្រជែ ។ Cat5e (1Gbps), Cat6 (10Gbps), Cat8 (40Gbps) ។

📺 Coaxial

មាន Inner Conductor, Insulator, Shield, Outer Jacket ។ ប្រើ Cable TV, Old Ethernet (10Base2) ។

💡 Fiber Optic

ប្រើ Light (photon) ជំនួស Electricity ។ Single-mode (ចម្ងាយ) vs Multi-mode (ខ្លី) ។

Wireless (Unguided) Media
ប្រភេទFrequencyចម្ងាយការប្រើប្រាស់
Radio Wave3 kHz – 1 GHzគ្មានដែនFM Radio, WiFi, LTE
Microwave1 GHz – 300 GHz50+ kmSatellite, 5G Backhaul, WiMAX
Infrared300 GHz – 400 THzខ្លី (ចន្លោះ)Remote Control, IrDA
Satelliteខ្ញបៗGlobalGPS, Starlink, DirectTV
🟢 Basic — មេរៀនទី ៤

Digital Encoding

Line Coding (NRZ, RZ, Manchester, Differential Manchester), Block Coding, Scrambling ។

Line Coding Schemes
Schemeការពិពណ៌នាDC ComponentSync
NRZ-L (Non-Return-to-Zero Level) 1=High, 0=Low — ថេរ មាន ខ្សោយ
NRZ-I (NRZ Inverted) 1=ប្ដូរ Level, 0=ថេរ មាន ប្រសើរ
Manchester 1=High→Low, 0=Low→High ។ Transition ពាក់កណ្ដាល bit គ្មាន ល្អ
Differential Manchester 1=គ្មាន Transition ដើម, 0=មាន Transition ដើម គ្មាន ល្អ
AMI (Alternate Mark Inversion) 0=Zero Voltage, 1=+/-V ស្លប់គ្នា គ្មាន មធ្យម
4B/5B រៀងរាល់ 4 bits encode ជា 5 bits គ្មាន ល្អ
Manchester Encoding — Data: 1 0 1 1 0
1 0 1 1 0 H L
Analog-to-Digital Conversion
〰️ Analog
Input
→
📏 Sampling
Nyquist
→
🔢 Quantizing
Level
→
💾 Encoding
Binary
→
Digital
Output
Nyquist Sampling Rate
Sampling Rate ≥ 2 × Highest Frequency
Audio 20kHz → Sample Rate ≥ 40,000 samples/sec → CD: 44,100 Hz
🟢 Basic — មេរៀនទី ៥

Multiplexing

FDM, TDM, WDM, OFDM — ការចែករំលែក Bandwidth ក្នុង Single Medium ។

ប្រភេទ Multiplexing
ប្រភេទការពណ៌នាការប្រើប្រាស់
FDM
Frequency Division		 ចែក Bandwidth ជា Sub-Channels តាម Frequency ។ ស្ដើៗ run ក្នុងពេលតែមួយ Cable TV, Analog Phone, FM Radio, DSL
TDM
Time Division		 ចែក Time ជា Slots ។ User ម្នាក់ប្រើ Slot ១ ។ Synchronous vs Statistical T1/E1 Line, ISDN, GSM
WDM
Wavelength Division		 Fiber Optic — ចែក Wavelength (Color) ។ DWDM: 100+ channels per fiber Fiber Optic Internet Backbone
OFDM
Orthogonal FDM		 Sub-carriers ចំហៀៗ គ្នា (Orthogonal) — ប្រឆាំង Multipath WiFi (802.11a/g/n/ac), 4G LTE, 5G
CDMA
Code Division		 User ម្នាក់ប្រើ Code (Chip Sequence) ពិសេស — share Frequency+Time 3G, GPS, CDMA Phone
TDM vs FDM Diagram

FDM — ចែក Frequency

f₁: User A (88-92 MHz)
f₂: User B (92-96 MHz)
f₃: User C (96-100 MHz)

TDM — ចែក Time Slots

A
T1
B
T2
C
T3
A
T4
B
T5
C
T6
🟠 Intermediate — មេរៀនទី ៦

Data Link Layer

OSI Layer 2, Framing, MAC Address, Ethernet, CSMA/CD, CSMA/CA, Error Detection, Flow Control ។

Data Link Layer — Layer 2

Data Link Layer ទទួលខុសត្រូវ: Framing (ដាក់ Data ជា Frame), Physical Addressing (MAC Address), Error Control, Flow Control, Access Control ។

Frame Structure
Preamble Dst MAC Src MAC Type/Len Data/Payload FCS/CRC
MAC Address

48-bit Hardware Address ។ ប្រើ Hexadecimal ។

AA:BB:CC:DD:EE:FF
OUI (3 bytes) + NIC (3 bytes)
CSMA/CD & CSMA/CA
CSMA/CD

Collision Detection — ប្រើដោយ Ethernet (Wired) ។

  • Carrier Sense — ស្ដាប់ Medium
  • Multiple Access — ច្រើននាក់ share
  • Collision Detection — ស្ដាប់ Collision
  • ប្រសិន Collision → Stop → Wait Random → Retry
CSMA/CA

Collision Avoidance — ប្រើដោយ WiFi (Wireless) ។

  • ស្ដាប់ Medium មុនផ្ញើ
  • ប្រើ RTS/CTS (Request/Clear To Send)
  • Random Backoff ជៀសវាង Collision
  • ACK បញ្ជាក់ទទួល Frame
🟠 Intermediate — មេរៀនទី ៧

Network Layer & IP

IP Address (IPv4/IPv6), Subnetting, CIDR, Routing Protocols (RIP, OSPF, BGP), NAT, ARP ។

IPv4 Address

IPv4 ជា 32-bit address ។ សរសេរជា Dotted Decimal ។ មាន 4.3 Billion addresses ។

192.168.1.100
11000000.10101000.00000001.01100100
ClassRangeDefault Maskប្រើ
A1.0.0.0 – 126.255.255.255/8 (255.0.0.0)Large Network
B128.0.0.0 – 191.255.255.255/16 (255.255.0.0)Medium Network
C192.0.0.0 – 223.255.255.255/24 (255.255.255.0)Small Network
D224.0.0.0 – 239.255.255.255—Multicast
E240.0.0.0 – 255.255.255.255—Reserved/Research
CIDR Subnetting
192.168.1.0/24 → 256 hosts (254 usable)
192.168.1.0/25 → 128 hosts per subnet × 2 subnets
Usable hosts = 2ⁿ – 2 (ដក Network + Broadcast)
IPv6 & Routing Protocols
IPv6

128-bit = 340 Undecillion addresses ។ Format: 2001:db8::1

  • No NAT needed
  • Built-in IPsec Security
  • Auto-configuration (SLAAC)
  • Better Multicast support
Routing Protocols
  • RIP — Distance Vector, max 15 hops
  • OSPF — Link State, Fast Convergence
  • EIGRP — Cisco Hybrid Protocol
  • BGP — Internet Routing (ISP to ISP)
  • ICMP — Ping, Traceroute
🟠 Intermediate — មេរៀនទី ៨

Transport Layer

TCP vs UDP, Port Numbers, 3-Way Handshake, Flow Control, Congestion Control, Socket ។

TCP vs UDP
FeatureTCPUDP
ConnectionConnection-orientedConnectionless
ReliabilityReliable (ACK, Retransmit)Unreliable (Best Effort)
OrderIn-order deliveryNo ordering
Speedយឺតជាង (overhead)លឿន (less overhead)
Header Size20 bytes+8 bytes
Use CasesHTTP, FTP, Email, SSHDNS, DHCP, Video Stream, VoIP, Gaming
TCP 3-Way Handshake
CLIENT
SERVER
CLOSED
→ SYN (seq=x)
LISTEN
SYN SENT
← SYN+ACK (seq=y, ack=x+1)
SYN RCVD
ESTABL.
→ ACK (ack=y+1)
ESTABL.
💡

TCP 4-Way Handshake ប្រើដើម្បី Close Connection — FIN → ACK → FIN → ACK ។

🟠 Intermediate — មេរៀនទី ៩

Wireless & WiFi

WiFi Standards (802.11), Bluetooth, WiMAX, Cellular (2G/3G/4G/5G), Infrared, Satellite Internet ។

WiFi (IEEE 802.11) Standards
Standardឈ្មោះFrequencyMax SpeedRange
802.11bWiFi 12.4 GHz11 Mbps35m
802.11aWiFi 25 GHz54 Mbps35m
802.11gWiFi 32.4 GHz54 Mbps38m
802.11nWiFi 42.4/5 GHz600 Mbps70m
802.11acWiFi 55 GHz3.5 Gbps35m
802.11axWiFi 6/6E2.4/5/6 GHz9.6 Gbps35m+
802.11beWiFi 72.4/5/6 GHz46 Gbps35m+
Cellular Networks Evolution
1G Analog Voice (AMPS) 1980s — Voice Only
2G GSM / CDMA — Digital 9.6 kbps – 384 kbps
3G UMTS / WCDMA / HSPA 384 kbps – 14.4 Mbps
4G LTE / LTE-Advanced 100 Mbps – 1 Gbps
5G NR (New Radio) — mmWave Up to 20 Gbps — Low Latency 1ms
🔴 Advanced — មេរៀនទី ១០

OSI Model & TCP/IP

OSI 7 Layers, TCP/IP 4 Layers, Protocol ក្នុងនីមួយៗ Layer, Data Encapsulation, PDU Names ។

OSI Model — 7 Layers
7Application LayerHTTP, FTP, SMTP, DNS, DHCP
6Presentation LayerSSL/TLS, JPEG, MPEG, Encryption
5Session LayerNetBIOS, SQL Session, RPC
4Transport LayerTCP, UDP, Port Numbers
3Network LayerIP, ICMP, ARP, Routing
2Data Link LayerEthernet, MAC, Switch
1Physical LayerCable, Hub, Bit Transmission
TCP/IP vs OSI + Data Encapsulation
TCP/IP LayerOSI LayersPDU NameDevices
Application7 + 6 + 5Data / MessageServer, PC
Transport4Segment (TCP) / Datagram (UDP)Firewall
Internet3PacketRouter
Network Access2 + 1Frame / BitSwitch, Hub
Data Encapsulation — Sender Side
Application:
[ DATA ]
Transport:
[TCP HDR | DATA ]
Network:
[IP HDR | TCP HDR | DATA ]
Data Link:
[ETH HDR | IP HDR | TCP HDR | DATA | FCS]
🔴 Advanced — មេរៀនទី ១១

Network Security

Threats (DoS, MITM, Phishing), Encryption (Symmetric/Asymmetric), Firewall, VPN, SSL/TLS, Digital Signature ។

ការគំរាមកំហែង Network
⚔️ Active Attacks
  • DoS/DDoS — Flood packets ធ្វើ Server ដាច់
  • MITM — Man-in-the-Middle intercept
  • Replay Attack — ចម្លង + ផ្ញើ Packet ម្ដងទៀត
  • Spoofing — ក្លែងបន្លំ IP/MAC
🕵️ Passive Attacks
  • Eavesdropping — ស្ដាប់ Traffic
  • Traffic Analysis — វិភាគ Pattern
  • Phishing — ក្លែង Website
  • Sniffing — ចាប់ Packets
Encryption
Symmetric Encryption

ប្រើ Key តែមួយ Encrypt & Decrypt ។ លឿន ប៉ុន្ដែ Key Exchange ពិបាក ។

AES-256 DES 3DES ChaCha20
Asymmetric Encryption

ប្រើ Public + Private Key Pair ។ Public Key Encrypt, Private Key Decrypt ។ យឺត ប៉ុន្ដែ Safe ។

RSA-2048 ECC Diffie-Hellman
🔐

HTTPS ប្រើ Hybrid Encryption — Asymmetric (RSA/ECC) ដើម្បី Exchange Session Key, បន្ទាប់មកប្រើ Symmetric (AES) Encrypt Data ។

🔴 Advanced — មេរៀនទី ១២

Protocol Suite

HTTP/HTTPS, FTP, SMTP/POP3/IMAP, DNS, DHCP, SSH, SNMP — Port Numbers & Functions ។

Application Layer Protocols
ProtocolPortTransportការប្រើប្រាស់
HTTP80TCPWeb Pages (Unencrypted)
HTTPS443TCP/TLSSecure Web (SSL/TLS)
FTP20/21TCPFile Transfer
SFTP/SCP22TCP/SSHSecure File Transfer
SSH22TCPSecure Remote Shell
SMTP25/587TCPSend Email
POP3110/995TCPDownload Email
IMAP143/993TCPEmail Sync (Server-based)
DNS53UDP/TCPDomain → IP Resolution
DHCP67/68UDPAuto IP Assignment
SNMP161/162UDPNetwork Management
RDP3389TCPRemote Desktop
DNS Resolution Process
Browser
www.example.com
→
Local Cache
HIT?
→
Recursive
Resolver
→
Root DNS
.com NS?
→
TLD Server
example.com NS?
→
Authoritative
93.184.216.34
🔴 Advanced — មេរៀនទី ១៣

Error Detection & Correction

Parity Bit, CRC, Hamming Code, Checksum, Forward Error Correction (FEC), ARQ Protocols ។

Error Detection Methods
Methodការពណ៌នាភាព Detectការប្រើ
Parity Bit បន្ថែម 1 bit ដើម្បីឱ្យ 1s ជាចំនួនគូ (Even) ឬ សេស (Odd) 1-bit error Simple memory check
Checksum បូក bytes ទាំងអស់ → 1s complement → ផ្ញើ Multiple bits IP, TCP, UDP header
CRC (Cyclic Redundancy Check) Polynomial Division — Remainder ជា CRC code Burst errors Ethernet, WiFi, Disk
Hamming Code Error Detection + Correction — ប្រើ Parity bits ច្រើន 2-bit detect, 1-bit correct RAM ECC, Telecom
ARQ — Automatic Repeat Request
Stop-and-Wait

ផ្ញើ Frame ១ → Wait ACK → ផ្ញើ Frame ២ ។ ស្ទើរ ប៉ុន្ដែ ងាយ ។

Efficiency = T_frame / (T_frame + 2×T_prop)
Go-Back-N

ផ្ញើ N Frames ។ Error → ផ្ញើ Error Frame + Frames ក្រោយ ម្ដងទៀត ។ Window Size = N-1 ។

Selective Repeat

ផ្ញើ Window ។ Error → ផ្ញើ Error Frame តែ ១ ។ ប្រើ Buffer ។ Efficient ជាង ។

🔴 Advanced — មេរៀនទី ១៤

Internet & Cloud

Internet Architecture, ISP Tiers, CDN, Cloud Computing (IaaS/PaaS/SaaS), SDN, NFV, Edge Computing ។

Internet Structure
Tier 1 ISP AT&T, NTT, Telia — Global Backbone (no upstream)
Tier 2 ISP Regional ISPs — Peer with Tier 1
Tier 3 ISP Local ISPs — ផ្ដល់ Internet ដល់ End Users
End Users Homes, Businesses, Mobile
Cloud Computing Models
IaaS

Infrastructure as a Service — VM, Storage, Networking ។ ឧ: AWS EC2, Azure VM, GCP Compute ។

PaaS

Platform as a Service — Dev Environment, DB, Runtime ។ ឧ: Heroku, AWS Elastic Beanstalk, Google App Engine ។

SaaS

Software as a Service — Ready-to-use Apps ។ ឧ: Gmail, Zoom, Salesforce, Office 365 ។

⚡

SDN (Software Defined Networking) — ញែក Control Plane ពី Data Plane ។ Network ត្រូវបានគ្រប់គ្រងដោយ Software Controller ទៅ Switches ពីចម្ងាយ ។

🔴 Advanced — មេរៀនទី ១៥

5G & Future Tech

5G Architecture (RAN/Core), Network Slicing, IoT, eMBB/mMTC/URLLC, 6G Research, Quantum Networking ។

5G — New Radio (NR)
eMBB

Enhanced Mobile Broadband — ល្បឿន Data ខ្ពស់ (20 Gbps) ។ 8K Video, AR/VR ។

mMTC

Massive Machine Type Comm — ១ km² = ១ million devices ។ IoT Sensors, Smart City ។

URLLC

Ultra-Reliable Low Latency — 1ms Latency, 99.9999% Reliability ។ Self-driving, Surgery Robot ។

Feature4G LTE5G NR6G (2030+)
Peak Speed1 Gbps20 Gbps1 Tbps
Latency30-50 ms1 ms0.1 ms
Frequency700 MHz–2.5 GHz1–100 GHz100 GHz–10 THz
Connection Density100K/km²1M/km²10M/km²
Future Technologies
🔮 Quantum Networking
  • Quantum Key Distribution (QKD)
  • Quantum Entanglement Communication
  • Hack-proof Encryption
  • Quantum Internet (2030+)
🛰️ Satellite Internet
  • Starlink (SpaceX) — LEO Satellites
  • OneWeb — Global Coverage
  • Amazon Kuiper
  • Latency 20-40ms (LEO)
🎉

សូមអបអរ! អ្នកបានបញ្ចប់មេរៀន Data Communication ទាំងអស់ ១៥ — ពី Signal Basics រហូតដល់ 5G, Cloud, Quantum Networking! ជំហានបន្ទាប់: Computer Networks (Tanenbaum), CCNA Certification, Network+ !