Symmetric encryption uses a single key for both encryption and decryption, making it faster but requiring secure key exchange. Asymmetric encryption employs a public-private key pair, ensuring secure communication without a prior key exchange but being slower due to the complexity of operations. Symmetric encryption is suitable for data at rest, like stored files, while asymmetric encryption is ideal for secure communication over networks, such as SSL/TLS protocols.

To diagnose slow network performance using the OSI Model, start at the Physical Layer (Layer 1) to check for issues like cable damage, connectivity problems, or hardware failures. Move up to the Data Link Layer (Layer 2) to examine Ethernet or MAC address problems. The Network Layer (Layer 3) is critical for diagnosing routing or IP address issues that could cause delays. Finally, the Transport Layer (Layer 4) helps identify congestion, packet loss, or protocol-related problems. Solutions may involve replacing faulty hardware, optimizing routing tables, or implementing Quality of Service (QoS) measures.

Bubble sort exhibits quadratic time complexity in the worst-case scenario. This happens when the array is in reverse order or nearly sorted, causing the algorithm to make a large number of comparisons and swaps for each element, leading to a time complexity of O(n^2).

UDP (User Datagram Protocol) and TCP (Transmission Control Protocol) differ primarily in their reliability and speed characteristics. UDP is faster than TCP but less reliable, as it does not guarantee packet delivery. On the other hand, TCP is slower but more reliable due to its mechanisms such as acknowledgment, retransmission, and flow control, ensuring that data reaches its destination accurately and in order. TCP is commonly used for applications that require high reliability, such as web browsing and file transfers, while UDP is suitable for real-time applications like video streaming and online gaming where speed is prioritized over data integrity.

The correct option is "Internet." In the TCP/IP model, packet routing occurs at the Internet layer (Layer 3). This layer is responsible for addressing, routing, and delivering packets between different networks. The Internet Protocol (IP) operates at this layer, providing the necessary functions for packet routing across the Internet.

The Proxy design pattern acts as a surrogate or placeholder for another object and controls access to it. On the other hand, the Decorator pattern dynamically adds new functionality to an object without altering its structure. Proxy focuses on controlling access, while Decorator focuses on adding responsibilities. Understanding these distinctions is crucial when deciding which pattern to use in a given context.

Merge sort has the best time complexity in the worst-case scenario among the given options. It has a time complexity of O(n log n) in all cases, making it efficient for large datasets. Quick sort can have a worst-case time complexity of O(n^2) in certain scenarios, making it less preferable for worst-case scenarios compared to merge sort.

Option 1 is correct. In an e-commerce application, optimizing queries for product recommendations involves indexing relevant attributes like product categories, user preferences, and purchase history. This speeds up retrieval by reducing search times. Query optimization techniques further enhance performance. NoSQL databases may offer scalability benefits but might not align with RDBMS concepts directly. Caching can improve performance but is secondary to optimizing queries. Complex SQL queries and normalization may not be optimal for recommendation systems due to performance overhead and complexity.

Cursor-based pagination using a timestamp or unique identifier is efficient for handling large datasets as it ensures stable pagination results even if items are added or removed. It also reduces the chances of duplicate or missing data during pagination.

JSON Web Tokens (JWT) are compact, self-contained tokens used for authentication in web apps. They are signed to ensure integrity and can carry user identity and other claims securely. OAuth tokens are different from JWTs, used for access delegation, while JWTs are used for stateful authentication. JWTs are often employed for session management, allowing servers to verify user authenticity and authorize access to resources securely.