Which broadband access technology uses Asynchronous Transfer Mode (ATM) as the Data Link layer protocol that terminates at a device known as the DSL access multiplexer (DSLAM)?

Introduction / Context:
Broadband access technologies must carry user data from customer premises to the service provider aggregation devices. Many Digital Subscriber Line deployments historically used Asynchronous Transfer Mode as the underlying Data Link layer technology between the customer modem and the provider DSL access multiplexer.

Given Data / Assumptions:

• The question refers to ATM as the Data Link layer protocol.
• The ATM based link is terminated at a DSL access multiplexer, commonly abbreviated DSLAM.
• Several WAN and broadband technologies are offered as choices.
• We must identify which technology matches this description.

Concept / Approach:
Digital Subscriber Line services, especially early ADSL variants, often encapsulated user traffic inside ATM cells on the copper local loop. The DSL modem at the customer premises connected over the telephone line to a DSLAM located at the provider central office. The DSLAM terminated the ATM circuits from many subscribers and passed traffic into the provider network. PPPoE is a higher layer encapsulation used by many DSL providers on top of Ethernet and potentially ATM, while Frame Relay and T1 represent different WAN technologies not tied specifically to DSLAMs.

Step-by-Step Solution:
1. Note the key hint: the Data Link protocol is ATM and it terminates at a DSLAM.2. Recall that DSL uses the existing copper phone line and that providers often used ATM over that line, terminated by a DSLAM at the central office.3. Recognize that PPPoE is not itself a physical or Data Link technology to the DSLAM; it commonly rides over Ethernet and possibly ATM, but the underlying broadband line is still DSL.4. Frame Relay and dedicated T1 links do not typically involve a DSLAM; they terminate on different types of provider equipment and use different protocols at the Data Link layer.5. Therefore, the broadband access technology that matches the description is DSL.

Verification / Alternative check:
Telecommunications diagrams for DSL deployments show the path from customer DSL modem to the DSLAM using ATM virtual circuits, with each subscriber mapped to specific virtual paths and channels. This model is well documented and widely used by service providers.

Why Other Options Are Wrong:
Option B, PPPoE, describes an encapsulation used at higher layers that can run over DSL but is not the Data Link technology terminating at the DSLAM. Option C, Frame Relay, is a packet switched WAN service that uses DLCIs and does not connect to a DSLAM. Option D, T1, is a dedicated digital leased line service that does not rely on DSLAMs or ATM cells in the same way as DSL circuits.

Common Pitfalls:
Some learners confuse PPPoE with DSL because both appear together in broadband configurations. It helps to remember that PPPoE is a session and encapsulation mechanism, while the actual copper line and DSLAM based infrastructure correspond to DSL technology. Focusing on the keyword DSLAM, which is specific to DSL networks, quickly leads you to the correct answer.

Final Answer:
Digital Subscriber Line (DSL)