Acme Corporation wants to provide dial-up remote access so branch employees can connect to the local network. The company uses multiple routed protocols, requires user authentication, and wants callback support to reduce long-distance charges. Which protocol is the best choice for these remote dial-up services?

Introduction / Context:
Before broadband and VPN technologies became widespread, dial-up remote access was a common way for employees to connect to corporate networks. Several protocols can operate over serial and dial-up links, but only some provide the features needed for modern remote access, such as multiprotocol support, authentication, and callback.

Given Data / Assumptions:

• The company wants to enable dial-up services for remote office employees.
• The network carries multiple routed protocols across the link, not just IP.
• User authentication is required so only authorized employees can connect.
• Callback support is desired to control telephone charges.
• The question asks which protocol best meets all these requirements.

Concept / Approach:
Point-to-Point Protocol (PPP) was designed to support multiple network layer protocols over serial links. It includes Link Control Protocol to manage the link and Network Control Protocols for different routed protocols such as IP and IPX. PPP also supports authentication methods like PAP and CHAP and can provide callback features. HDLC is simpler and usually supports only a single protocol in Cisco implementations, and it lacks standardized authentication and callback. Frame Relay is a packet switched WAN technology rather than a dial-up remote access protocol. Generic IEEE 802.1 is not specific to dial-up services.

Step-by-Step Solution:
1. Confirm that multiple routed protocols must traverse the dial-up connection.2. Recognize that PPP includes separate Network Control Protocols for multiple routed protocols, so it supports this requirement.3. Confirm that user authentication is needed; PPP supports PAP and CHAP to authenticate dial-in users.4. Confirm that callback support is desired; PPP supports callback mechanisms to return calls to users, helping control costs.5. Comparing all options, PPP is the only protocol that matches all these capabilities for dial-up remote access.

Verification / Alternative check:
Dial-up remote access server configuration examples in Cisco and other vendor documentation almost always use PPP as the encapsulation protocol. These examples show PAP or CHAP authentication and often discuss callback options, reinforcing that PPP is the correct solution for this set of requirements.

Why Other Options Are Wrong:
Option A, IEEE 802.1, refers broadly to LAN bridging standards and does not describe a specific dial-up remote access protocol. Option B, Frame Relay, is a WAN technology designed for permanent virtual circuits rather than modem dial-up access by individual users. Option C, HDLC, is a simple point-to-point encapsulation that in Cisco form is proprietary and typically limited to IP, without built-in authentication or callback features.

Common Pitfalls:
Students sometimes think of HDLC and PPP as interchangeable because both operate on serial links. However, PPP provides a richer feature set ideal for remote access, including authentication and protocol negotiation, while HDLC focuses mainly on basic encapsulation. Recognizing these differences is vital for selecting the correct protocol in exam scenarios.

Final Answer:
Point-to-Point Protocol (PPP)