DPDC, Assistant Engineer (CSE), 2025 ok all

1. Which transmission medium is used in LAN? Write their maximum length and capacity.

Transmission Media Used in LAN (with Length & Capacity)

1. Twisted Pair Cable (UTP/STP)
This is the most common medium used in Ethernet LANs.

Maximum Length: 100 meters (328 feet)
Capacity:
- Cat5e: 1 Gbps
- Cat6: 1 Gbps (10 Gbps up to 55m)
- Cat6a/Cat7: 10 Gbps

2. Fiber Optic Cable
Used for high-speed communication and long-distance connections.

Maximum Length:
- Multimode (MMF): 550m – 2 km
- Single-mode (SMF): 10 km – 100 km+
Capacity:
- MMF: 10 Gbps – 100 Gbps
- SMF: 10 Gbps, 40 Gbps, 100 Gbps+

3. Coaxial Cable
Used in older Ethernet networks and some industrial systems.

Maximum Length:
- Thinnet (10Base2): 185 meters
- Thicknet (10Base5): 500 meters
Capacity: 10 Mbps – 100 Mbps

4. Wireless LAN (Wi-Fi)
Used for wireless communication using radio waves.

2. In the TCP/IP model, how is data known in different layers.

3. Why DFS better than BFS? Explain.

Depth First Search (DFS) is better than Breadth First Search (BFS) in some cases due to the following reasons:

Less Memory Usage: DFS uses a stack and stores fewer nodes compared to BFS (which uses a queue).
Suitable for Deep Search: DFS is efficient when the solution is far from the root (deep in the graph).
Faster for Some Problems: DFS can find a solution faster without exploring all nodes at the same level.
Useful in Backtracking: DFS is widely used in problems like maze solving, cycle detection, topological sorting.
Simple Implementation: Can be implemented easily using recursion.

Note:
DFS is not always better; BFS is better when shortest path is required.

কিছু ক্ষেত্রে Depth First Search (DFS), Breadth First Search (BFS)-এর চেয়ে বেশি কার্যকর:

কম Memory ব্যবহার: DFS stack ব্যবহার করে, তাই কম node store করে; BFS-এ বেশি memory লাগে।
Deep Search-এর জন্য উপযুক্ত: যখন solution graph-এর গভীরে থাকে, DFS বেশি কার্যকর।
দ্রুত ফলাফল: সব level explore না করে দ্রুত solution পেতে পারে।
Backtracking-এ ব্যবহার: maze, cycle detection, topological sorting-এ DFS বেশি ব্যবহৃত হয়।
সহজ Implementation: recursion দিয়ে সহজে implement করা যায়।

নোট:
DFS সব সময় ভালো নয়; shortest path খুঁজতে BFS বেশি উপযোগী।

4. Why is agile model better than waterfall model?

Flexibility: Agile allows changes at any stage, while Waterfall is rigid.
Customer Involvement: Continuous feedback from customers improves the product.
Faster Delivery: Working software is delivered in small increments.
Early Testing: Testing is done throughout development, reducing errors early.
Better Risk Management: Problems are identified and solved early.
Adaptability: Suitable for changing and complex requirements.

Conclusion:
Agile is better for modern projects because it is flexible, interactive, and delivers faster results compared to Waterfall.

Agile Model কেন Waterfall Model-এর চেয়ে ভালো

উপসংহার:
Agile বেশি flexible, দ্রুত এবং user-friendly হওয়ায় Waterfall-এর চেয়ে বেশি কার্যকর।

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