NAT (Network Address Translation) is a networking technique that modifies the IP address information in packet headers while the packets pass through a router or firewall.Its primary purpose is to map private (internal) IP addresses to public (external) IP addresses, and vice versa. Real-World ExampleSuppose two employees (e.g., Manager Hongcheol and Deputy Gayoung) each have private IP address..

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Time ComplexityTime complexity describes how the number of operations grows as the input size N increases.It measures how much time an algorithm takes, independent of hardware or programming language.We focus on the number of operations, not exact timings.To express it, we use Big-O notation, which reflects the most significant term in the function T(n) — the one that dominates as n grows. Comm..

What is a Thread?A thread is the smallest unit of execution within a process.A single process can have multiple threads.Unlike processes, which each have their own code, data, and heap,threads share the code, data, and heap of their process. → This allows multiple tasks to run concurrently within a single process.MultithreadingMultithreading is a technique where multiple threads within a process..

8/3refactor: transform IAP tests to call actual service methodsReplace duplicated business logic tests with real TAPService method callsAdd comprehensive error scenario testing for production edge casesRestructure test files for better organization:iapService.basic.test.ts: Real method testingiapService.unit.test.ts: Enhanced business logic testsiapService. integration.test.ts: Complex workflow ..

Addressing in OSI Layer 2 and Layer 3 In the OSI 7-layer model, only Layer 2 (Data Link Layer) and Layer 3 (Network Layer) use addressing schemes:Layer 2 uses a physical address, known as the MAC addressLayer 3 uses a logical address, known as the IP addressMAC Address (Layer 2)A MAC address is split into two 24-bit parts:OUI (Organizationally Unique Identifier): Assigned by IEEE to identify th..