Which OSI layer is charged with establishing, managing, and terminating connections between applications?

The correct answer is Layer 5, which is known as the Session Layer in the OSI model. This layer plays a crucial role in managing sessions, which are established connections between applications that allow them to communicate. Its primary responsibilities include initiating, maintaining, and terminating these communication sessions, ensuring that data exchange between applications is synchronized and organized.

Layer 5 uses various protocols to support these functionalities, facilitating the establishment of connections and ensuring that all parts of the communication are effectively managed. This includes handling session restoration in case of interruptions and providing mechanisms for managing dialogues, such as handling two-way communication.

In contrast, the other layers have different roles: Layer 4, known as the Transport Layer, is responsible for the end-to-end communication and reliability of the data transfer; Layer 3, the Network Layer, deals with routing packets across the network; and Layer 6, the Presentation Layer, handles data translation and encryption/decryption before the data is presented to the application layer. Each layer has distinct responsibilities that contribute to the overall functionality of the OSI model, but Layer 5 specifically focuses on managing sessions between applications, making it the correct choice for this question.