Gigabit Ethernet SX Uses Multimode Fiber | Generated by AI
Question: In Gigabit Ethernet 1000BASE-SX, which uses short-wavelength laser as the signal source, what is the transmission medium?
A. Coaxial cable
B. Single-mode fiber
C. Multimode fiber
D. Category 5 or Category 5e UTP
Answer:
C. Multimode fiber
Detailed explanation:
1000BASE-SX is one of the IEEE 802.3z Gigabit Ethernet standards introduced in 1998 (part of 802.3-1998). The naming breakdown is:
- 1000 = 1000 Mbps (1 Gbps)
- BASE = baseband transmission
- SX = Short-wavelength laser (850 nm), Multimode fiber
Key characteristics of 1000BASE-SX:
- Light source: 850 nm short-wavelength VCSEL (Vertical-Cavity Surface-Emitting Laser) or LED in early implementations
- Transmission medium: Multimode optical fiber (MMF)
- Most common: 62.5/125 µm multimode fiber → maximum distance 275 meters (full-duplex)
- 50/125 µm multimode fiber → maximum distance 550 meters (full-duplex)
- Connector types: Typically SC or LC duplex connectors
- Designed for short to medium reach inside buildings (data centers, backbone links, campus networks)
Why not the other options?
- A. Coaxial cable — Used in older Ethernet standards (10BASE5, 10BASE2), not for Gigabit Ethernet
- B. Single-mode fiber — Used in 1000BASE-LX (long-wavelength 1310 nm) and 1000BASE-LX10/ZX standards for much longer distances (up to 5–70 km), not SX
- D. Category 5 or 5e UTP — Used in 1000BASE-T (copper twisted-pair standard), which reaches up to 100 meters over four pairs of Cat 5e/Cat 6 cable, not optical SX
Quick comparison of common 1000BASE variants:
| Standard | Medium | Wavelength | Max Distance (full-duplex) |
|---|---|---|---|
| 1000BASE-SX | Multimode fiber | 850 nm | 275 m (62.5 µm) / 550 m (50 µm) |
| 1000BASE-LX | Single-mode or multimode | 1310 nm | 550 m (MMF) / 5–10 km (SMF) |
| 1000BASE-T | Cat 5e / Cat 6 UTP | — | 100 m |
Your answer (C) was correct.
References:
- None (standard IEEE 802.3 Gigabit Ethernet specification knowledge)