A hub is a physical layer device that simply repeats incoming signals to all of its ports, creating a single collision domain. A switch is a data link layer device that learns MAC addresses and uses them to intelligently forward frames only to the intended recipient, creating separate collision domains for each port.

TCP CUBIC is a congestion control algorithm that is the default in many Linux kernels. Unlike traditional Reno which uses linear window growth, CUBIC uses a cubic function to scale the congestion window based on the time since the last congestion event. This makes it more efficient and fair on high-bandwidth, high-latency networks (long fat pipes).

The exposed node problem occurs when a node is near a transmitter but not the receiver. Because the node senses the medium as busy, it refrains from sending its own data to a different recipient, even though its transmission would not actually interfere with the ongoing communication. This leads to inefficient use of the wireless spectrum.

The original TCP/IP model combined several functions into one 'Application' layer. In the more granular 7-layer OSI model, these functions are separated into the Session (dialogue control), Presentation (data formatting/encryption), and Application (network services for software) layers.

VPN stands for Virtual Private Network. This technology creates a secure and encrypted 'tunnel' over a public network, such as the internet. By doing so, it allows users to send and receive data across shared or public networks as if their computing devices were directly connected to a private network, thereby ensuring enhanced privacy and security for their online activities. This is crucial for protecting sensitive information from potential eavesdroppers or data breaches when using public Wi-Fi or accessing remote resources securely.

A firewall acts as a critical network security system, monitoring and controlling incoming and outgoing network traffic. It operates based on a set of predefined security rules, creating a robust barrier between a trusted internal network and an untrusted external network, such as the internet. Its primary function is to block unauthorized access while permitting legitimate traffic, thereby safeguarding the network from various cyber threats. Option A, an Intrusion Prevention System (IPS), is similar but focuses more on actively blocking detected threats rather than just filtering traffic based on rules. Option C, Secure Socket Layer (SSL) (now largely Transport Layer Security - TLS), is a protocol for encrypting communication between a web server and a web browser, not a system for blocking network access. Option D, Antivirus Software, protects individual devices from malicious software but does not control network-wide access.

NAT, while conserving IPv4 addresses, masks internal IP addresses behind a single public IP. This makes it difficult for external devices to initiate connections to specific internal devices directly, complicating services that rely on end-to-end connectivity like peer-to-peer applications.

Cloud Computing is an IT service delivery model where computing resources (like servers, storage, databases, networking, software, analytics, and intelligence) are provided as services over the internet ('the cloud') on an on-demand basis. Users can access these services without owning or directly managing the physical infrastructure, paying only for what they use. This contrasts with: * **Distributed Computing:** This involves multiple computers working together to solve a single problem, often across a network, but doesn't necessarily imply delivery 'as a service' or on-demand resource provisioning. * **Parallel Computing:** This is a type of computation in which many calculations or the execution of processes are carried out simultaneously. It focuses on the processing method rather than the delivery model. * **Virtual Computing (or Virtualization):** This is a technology that creates virtual versions of hardware resources (like servers or operating systems). While foundational to cloud computing, it describes the underlying technology rather than the service delivery model itself.

The Dark Web is a part of the internet that is not indexed by standard search engines and requires specific software, configurations, or authorizations to access, most commonly Tor. It is often used for anonymity, both for legitimate and illicit purposes.

VPN stands for Virtual Private Network. This technology creates a secure, encrypted 'tunnel' over a public network, like the internet, allowing users to send and receive data as if their computing devices were directly connected to the private network. This enhances privacy and security by masking the user's IP address and encrypting their online activities, protecting data from potential eavesdropping or interception.