When a VPN establishes a private link over the internet, this process is commonly referred to as "Tunneling." Tunneling involves encapsulating the data within a secure and encrypted connection, creating a virtual tunnel through which data can safely travel over the public internet, ensuring confidentiality and integrity.

In a Star topology, adding or removing devices can be done without disrupting the network. In a Star network, all devices are connected to a central hub or switch. If you need to add or remove a device, you can do so without affecting the connectivity of other devices. However, the central hub or switch represents a single point of failure.

In a TCP three-way handshake, the server responds to the client's SYN (synchronize) packet with a SYN-ACK (synchronize-acknowledgment) packet. This process is a critical part of establishing a reliable connection between the client and server.

TCP (Transmission Control Protocol) includes built-in mechanisms for handling network congestion. It uses techniques like sliding window flow control and congestion avoidance to ensure reliable data delivery and manage network congestion efficiently.

Sarah is analyzing the MAC address, which is a part of the frame header. The MAC address is a hardware address associated with the source device. A discrepancy in this address might indicate address spoofing, which can be a security concern.

Demodulation is the technique used to convert received analog signals back into their original digital form. It's the reverse process of modulation and is crucial in the reception of data in analog communication systems.

The Cyclic Redundancy Check (CRC) method uses polynomial division to detect changes in raw data. It is a widely used error detection technique that adds a mathematical value (CRC) to the data, which is then transmitted. The recipient performs a similar calculation and compares it with the received CRC to check for errors.

POP3 (Post Office Protocol version 3) is typically used when a user wants to download emails from a mail server to a local device and remove them from the server. It is designed for receiving emails.

Port Address Translation (PAT) is a variation of Network Address Translation (NAT) in which multiple devices on a local network are translated to a single public IP address, with different port numbers to keep track of which internal device the traffic belongs to. This enables multiple internal devices to share a single public IP address.

SMTP (Simple Mail Transfer Protocol) is primarily used for sending or relaying email messages between a client and a server or between servers. It's responsible for the delivery of outgoing emails, making it a crucial part of email communication.