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220-1201 Practice Question: A technician is troubleshooting a DSL connection…
A technician is troubleshooting a DSL connection that syncs at only 1.5 Mbps when the plan is 10 Mbps. The line is 12,000 feet from the central office. What is the most likely cause?
⚠ Common exam trap
The 220-1201 exam often tests the misconception that DSL speeds are always limited by the service plan rather than physical-layer constraints, leading candidates to overlook distance as the primary factor when sync rates are far below the plan speed.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The distance from the central office is too great.
DSL speeds degrade significantly with distance due to signal attenuation and noise. At 12,000 feet from the central office, ADSL2+ typically cannot sustain 10 Mbps; 1.5 Mbps is consistent with the maximum achievable rate at that distance. The sync rate is determined by line conditions, not the plan speed, making distance the primary limiting factor.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The modem is defective.
Why it's wrong here
A defective DSL modem would typically manifest as a complete inability to establish a physical layer connection, resulting in no sync at all, or highly unstable and frequently dropping connections. If a modem consistently syncs at a lower speed, it usually indicates a line quality issue rather than a hardware fault within the modem itself, which would likely cause more severe operational failures or complete loss of service.
- ✓
The distance from the central office is too great.
Why this is correct
DSL technology relies on transmitting data over copper telephone lines, where signal strength naturally attenuates with increasing distance from the Digital Subscriber Line Access Multiplexer (DSLAM) at the central office. Greater distances lead to a lower signal-to-noise ratio (SNR), forcing the DSL modem to negotiate a lower, more stable sync rate to maintain connection integrity. This physical limitation directly reduces the maximum achievable bandwidth.
- ✗
The router's firmware needs updating.
Why it's wrong here
A router's firmware primarily governs its operational logic, network protocols, routing decisions, and security features, not the physical layer synchronization speed of the DSL modem component. While a router might integrate a DSL modem, firmware updates for the router section itself do not alter the fundamental electrical characteristics or line quality that determine the DSL sync rate. Such updates address software bugs or add new functionalities, not physical layer performance.
- ✗
The ISP is throttling the connection.
Why it's wrong here
ISP throttling is a policy-driven reduction of available bandwidth that occurs at the network or application layer, *after* the physical DSL connection has successfully established its maximum possible sync rate. Throttling limits the actual data throughput experienced by the user, but it does not alter the underlying physical layer sync speed negotiated between the DSL modem and the DSLAM. The modem would still report its full sync rate, even if data transfer is artificially restricted.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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