RCDD · Question #212
The loop distance range in an "ethernet in the first mile" (EFM) design is:
The correct answer is C. 6.1 km (3.8 mi). The IEEE 802.3ah Ethernet in the First Mile (EFM) standard specifies a copper loop distance range of approximately 6.1 km (3.8 miles) for its 2BASE-TL variant under defined operating conditions.
Question
The loop distance range in an "ethernet in the first mile" (EFM) design is:
Options
- A2 km (1.2 mi)
- B4.8 km (3 mi)
- C6.1 km (3.8 mi)
- D9.7 km (6 mi)
- E12 km (7.5 mi)
How the community answered
(27 responses)- A4% (1)
- C85% (23)
- D7% (2)
- E4% (1)
Why each option
The IEEE 802.3ah Ethernet in the First Mile (EFM) standard specifies a copper loop distance range of approximately 6.1 km (3.8 miles) for its 2BASE-TL variant under defined operating conditions.
2 km is consistent with 10BASE-T or Fast Ethernet segment limits over copper, not the extended reach defined for EFM/2BASE-TL.
4.8 km (3 mi) does not correspond to a defined EFM loop distance specification in IEEE 802.3ah.
IEEE 802.3ah defines EFM copper (2BASE-TL) with a maximum loop reach of approximately 6.1 km (3.8 mi) at the specified data rate over a single twisted pair, targeting last-mile subscriber access. This reach figure is the defining design parameter of the EFM copper specification and distinguishes it from shorter-reach Fast Ethernet variants. The 6.1 km value reflects the physical layer reach supported by the PAM-5 line coding used in 2BASE-TL.
9.7 km (6 mi) exceeds the copper loop distance defined in the EFM standard; this range is more applicable to DSL technologies such as ADSL2+.
12 km (7.5 mi) is within the reach of fiber-based EFM variants (100BASE-BX10) or long-reach DSL, not the copper loop specification.
Concept tested: IEEE 802.3ah Ethernet in the First Mile copper loop distance
Source: https://standards.ieee.org/ieee/802.3ah/1348/
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