Which of the following terms best describes the creation of private virtual networks across a shared public Internet infrastructure, providing privacy through encryption and allowing the tunneling of non IP or legacy protocols inside secure connections?

Introduction / Context:
This question addresses the high level concept of building private communications over a shared public network such as the Internet. Organizations frequently need to connect remote offices and users securely without deploying dedicated leased lines everywhere. To do this they use technologies that create private tunnels over a public infrastructure so that traffic remains confidential and sometimes can carry non native protocols.

Given Data / Assumptions:
- The public underlying network is IP based, for example the global Internet.
- The solution must create private networks across this shared infrastructure.
- The mechanism should provide privacy, usually via encryption, and support tunneling of additional protocols inside the secure channel.
- Several technologies are listed, some of which relate to lower layer encapsulation or access methods rather than private overlay networks.

Concept / Approach:
The general term that describes creating a logically private network over a public infrastructure is Virtual Private Network or VPN. VPNs can be implemented using various underlying technologies, such as IPSec, Secure Sockets Layer, or Multiprotocol Label Switching, but the overarching idea remains the same: traffic is encapsulated and usually encrypted to form a private tunnel between sites or users. The question asks for this broad concept rather than any one implementation protocol.

Step-by-Step Solution:
Step 1: Identify keywords in the question such as private networks, across the Internet, privacy, and tunneling of non native protocols.Step 2: Recall that these terms collectively describe what VPN solutions provide to enterprises.Step 3: Recognize that IPSec is one common protocol suite used inside VPNs but is narrower in scope than the concept of a VPN itself.Step 4: Rule out other options such as HDLC, cable, and Frame Relay, which refer to link layer encapsulation or physical access methods rather than virtual overlays over the public Internet.Step 5: Select Virtual Private Network technology as the correct answer.

Verification / Alternative check:
In everyday networking language, engineers talk about setting up a site to site VPN tunnel between two branch offices or enabling remote access VPN for teleworkers. These phrases clearly match the description in the question. Although many of these deployments use IPSec under the hood, what the user experiences is a private virtual network connection riding on top of the public Internet, confirming that VPN is the correct general term.

Why Other Options Are Wrong:
HDLC is a data link layer protocol used for encapsulating network layer protocols over serial lines and does not in itself create private overlays across a public IP infrastructure. Cable refers to a broadband access medium that provides connectivity but not secure tunneling. IPSec is a protocol suite that can implement VPNs but is not the conceptual description requested here. Frame Relay PVCs are virtual circuits inside a provider network, not tunnels built across the open Internet.

Common Pitfalls:
One common pitfall is confusing a specific implementation, such as IPSec, with the broader concept of VPNs. Exams often distinguish between the conceptual term and the particular protocol used. Another mistake is to think that any dedicated service from a provider is automatically a VPN, even if it is simply a private leased line without tunneling or encryption over a public domain.

Final Answer:
The creation of private networks across the Internet with encrypted tunnels and protocol encapsulation is best described by the term Virtual Private Network VPN technology.