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এই পরীক্ষায় এই টপিক থেকে ২টি প্রশ্ন — TCP layer ও Triangulation।
বিকল্প: (ক) Application • (খ) Network • (গ) Transport ✓ • (ঘ) Data Link
TCP = OSI Layer 4 = Transport Layer। Reliable, connection-oriented, byte-stream।
Mnemonic: All People Seem To Need Data Processing
| Layer | Name | Function | Examples (Protocols) |
|---|---|---|---|
| 7 | Application | end-user interface | HTTP, FTP, SMTP, DNS, SSH |
| 6 | Presentation | data format, encryption | SSL/TLS, JPEG, MPEG, ASCII |
| 5 | Session | session establishment | NetBIOS, RPC, PPTP |
| 4 | Transport | reliable delivery, segmentation | TCP, UDP, SCTP |
| 3 | Network | routing, IP addressing | IP, ICMP, ARP, OSPF |
| 2 | Data Link | frame, MAC | Ethernet, PPP, Wi-Fi (802.11) |
| 1 | Physical | bits, electrical signals | Ethernet cable, Fiber, RJ-45 |
| বৈশিষ্ট্য | TCP | UDP |
|---|---|---|
| Connection | Connection-oriented (3-way handshake) | Connectionless |
| Reliability | Reliable (acknowledgment, retransmit) | Unreliable (best-effort) |
| Speed | Slower | Faster |
| Ordering | Maintains order | No order |
| Use cases | Web (HTTP), email (SMTP), file transfer (FTP) | DNS, VoIP, gaming, live streaming |
Client Server
│ │
│── SYN ─────────────────→│
│←─── SYN-ACK ────────────│
│── ACK ─────────────────→│
│ │
│ (Connection ready) │
Options: (ক) Shortest Path • (খ) Triangulation ✓ • (গ) Nearest-neighbour • (ঘ) Encryption
Cell Tower Triangulation — ৩+ tower-এর signal-strength/timing থেকে geometric triangulation।
Tower A
●
/\
/ \
/ \
/ 📱 \
/ \
/ \
Tower B ────── Tower C
| Method | Accuracy | বিবরণ |
|---|---|---|
| Cell Triangulation | ১০০m – ১km | Cell tower-এর signal |
| GPS | ৫–১০m | Satellite (4+ satellites needed) |
| A-GPS | ৩–৫m | Assisted GPS (cell + satellite + Wi-Fi) |
| Wi-Fi Positioning | ৫–১০m | Known Wi-Fi access points |
| Bluetooth Beacons | ১–৫m | Indoor positioning |
| NFC | ~১০cm | Very short range |
| Type | Range | উদাহরণ |
|---|---|---|
| PAN (Personal Area Network) | ১–১০m | Bluetooth, USB |
| LAN (Local Area Network) | ১০০m–১km | Office network, Home Wi-Fi |
| MAN (Metropolitan Area Network) | শহরব্যাপী | Cable TV network |
| WAN (Wide Area Network) | দেশ/বিশ্ব | Internet |
| Generation | Technology | Speed | Year |
|---|---|---|---|
| 1G | AMPS (analog) | 2.4 kbps | 1980s |
| 2G | GSM | 64 kbps | 1990s |
| 3G | UMTS | 2 Mbps | 2000s |
| 4G | LTE | 100 Mbps | 2010s |
| 5G | NR | 1-10 Gbps | 2019– |
| 6G | (research) | 100 Gbps+ | ~2030 |
| Topology | বিবরণ |
|---|---|
| Bus | একটি common cable-এ সব device |
| Star | কেন্দ্রীয় hub থেকে সব device |
| Ring | চক্রাকার connection |
| Mesh | প্রতিটি device সব device-এর সাথে |
| Tree | hierarchical, bus + star |
| Hybrid | একাধিক topology-এর সংমিশ্রণ |
| Version | Format | উদাহরণ |
|---|---|---|
| IPv4 | 32-bit, ৪ octets | 192.168.1.1 |
| IPv6 | 128-bit, ৮ groups of 16 bits | 2001:0db8:85a3::8a2e:0370:7334 |
IPv4 Classes:
| Class | First Octet | Use |
|---|---|---|
| A | 1–126 | Large networks |
| B | 128–191 | Medium |
| C | 192–223 | Small |
| D | 224–239 | Multicast |
| E | 240–255 | Experimental |
Private IP Ranges:
| Device | Function | OSI Layer |
|---|---|---|
| Hub | Repeats signal | Physical (1) |
| Switch | Filters by MAC | Data Link (2) |
| Router | Forwards by IP | Network (3) |
| Bridge | Connects two LANs | Data Link (2) |
| Gateway | Connects different networks | Application (7) |
| Modem | Modulates/demodulates signal | Physical (1) |
নেটওয়ার্ক ও কমিউনিকেশন — মূল লেকচার শিট — OSI ৭ layers বনাম TCP/IP ৪ layers, সব transport protocols (TCP/UDP), network types (PAN/LAN/MAN/WAN), topologies, IP addressing (IPv4/IPv6, classes, subnetting), network devices, wireless generations (1G-6G), routing algorithms, ও বাংলাদেশের telecom infrastructure।