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Difficulty: Very hardMobile Device Ports and Accessories

A corporate IT department deploys multi-monitor docking stations for mobile users equipped with laptops featuring USB Type-C physical ports. When connected to the docking station via a USB Type-C cable, the mobile device charges successfully and built-in USB peripheral ports on the dock function normally, but no video output is detected on the external dual monitors. Diagnostic testing confirms the external monitors and DisplayPort cables are fully functional, and all drivers are updated. Which of the following technical explanations best identifies why charging and USB data function properly while external video fails?

  1. The laptop's physical USB Type-C port lacks native host-controller support for DisplayPort Alternate Mode (Alt Mode), requiring a USB graphics adapter powered by DisplayLink software to drive external displays.Answer
  2. B
    The USB Type-C cable was inserted in a single-sided pin orientation, as physical USB Type-C connectors only route high-speed video signals along one side of the connector array.
  3. C
    The enterprise Mobile Device Management (MDM) profile enforcing full-device encryption has restricted peripheral hardware by automatically disabling physical video display interfaces.
  4. D
    The mobile device operating system requires active Exchange ActiveSync protocol synchronization before authorizing high-bandwidth video telemetry over external bus interfaces.

Answer

The host laptop's physical USB Type-C port does not feature hardware support for DisplayPort Alternate Mode, requiring a software-emulated USB graphics dock such as DisplayLink to output video.
The correct answer identifies that physical USB Type-C connector integration does not automatically imply support for DisplayPort Alternate Mode (Alt Mode). USB Type-C host ports must be wired specifically to support Alt Mode signal multiplexing. When Alt Mode is absent on the host laptop, standard display passthrough fails even though power delivery and standard USB data function normally. Resolving this requires a software-driven USB graphics dock (such as DisplayLink).

Step-by-Step Solution

1
Analyze the reported symptoms and functional interfaces.
Power Delivery (PD) and standard USB data transfer function properly, confirming physical cable contact, basic USB protocol operation, and power negotiation.
Isolating which functions work helps narrow down whether the issue is a physical hardware fault or a protocol capability mismatch.
2
Evaluate the requirement for native video over USB Type-C connectors.
Native video output across USB Type-C relies on Alternate Mode (e.g., DisplayPort Alt Mode or Thunderbolt), which requires dedicated physical routing hardware on the system motherboard and host controller.
A physical USB Type-C port does not automatically guarantee support for high-speed display protocols unless explicitly provisioned by the manufacturer.
3
Identify the proper workaround or root cause for non-Alt Mode Type-C host ports.
If the host controller lacks Alt Mode capabilities, video signals must be compressed and transmitted as standard USB data to a dock equipped with a DisplayLink controller and corresponding host OS drivers.
DisplayLink converts video frames into standard USB data packets, circumventing the need for native DisplayPort Alt Mode hardware lanes on the motherboard.

Key Concept

USB Type-C Connector Capabilities and Alternate Mode (Alt Mode) Routing
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Topics

Mobile Device Ports and Accessories

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