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.

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.

ICMP (Internet Control Message Protocol) is primarily used to diagnose network connectivity issues. It allows devices to send error and control messages, such as ping requests and responses, which are essential for network troubleshooting and diagnostics.

A "Burst Error" has occurred. A burst error is a sequence of consecutive bits in which more than one bit is altered during transmission, making it difficult to detect and correct. Single Bit Errors are easy to detect and correct, whereas burst errors can be more challenging.

The OSI (Open Systems Interconnection) model has 7 layers, which are used to standardize and understand network communication. The TCP/IP model, in contrast, has 4 layers. The two models have similarities, but the number of layers and their names differ.

In VPNs, "tunneling" refers to the process of encapsulating data within a secure protocol, often adding an additional layer of encryption to protect the data as it traverses an untrusted network (such as the internet). This ensures the confidentiality and integrity of the data being transmitted.

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.