Cisco Certified Network Associate (CCNA) Practice Exam

Which Layer 2 protocol encapsulation type supports both synchronous and asynchronous circuits?

1. HDLC

2. PPP

3. Frame Relay

4. Ethernet

The correct answer is: PPP

The correct answer is based on the capabilities of the Point-to-Point Protocol (PPP). PPP is a widely used Layer 2 protocol that provides the means to encapsulate multiple network layer protocols, including IP. One of its notable features is that it can operate over both synchronous and asynchronous circuits, making it extremely versatile for various types of network connections. Synchronous circuits involve a regular timing signal, which allows for efficient data transfer, while asynchronous circuits can transmit data without a shared clock signal, relying instead on start and stop bits for data synchronization. PPP's design accommodates both types of circuits, which contributes to its popularity and flexibility in networking environments. It also includes features such as error detection and link control, which enhance its reliability across these different types of connections. In contrast, while HDLC is specialized for synchronous communication and is generally not suitable for asynchronous circuits, Frame Relay is designed primarily for packet-switched networks and does not specifically address the characteristics of both synchronous and asynchronous communication. Ethernet primarily operates at Layer 2 but is not typically considered in the same context regarding synchronous/asynchronous layers as PPP. Hence, the choice of PPP is the most appropriate in this context.