Explanation: IPSec is a protocol for encrypting and authenticating packets during transmission between two parties and can involve any type of device, application, or service. The protocol performs both the authentication and negotiation of security policies between the two parties at the start of the connection and then maintains these policies throughout the lifetime of the connection. TLS operates at the application layer, not the network layer, and is widely used to secure communications between two parties. SSL is similar to TLS but has been deprecated. Although a VPN allows a secure channel for communications into a private network from an outside location, it’s not a protocol.