Cabling and media
Copper UTP categories, single-mode versus multimode fiber, Ethernet shared media and point-to-point connections, and Power over Ethernet.
Single-mode versus multimode fiber
| Property | Multimode (MMF) | Single-mode (SMF) |
|---|---|---|
| Core diameter | 50 µm (OM3/OM4) or 62.5 µm (OM1) | ~9 µm |
| Light source | LED/VCSEL, 850 nm | Laser, 1310/1550 nm |
| Modal dispersion | Limits reach | Negligible — one light path |
| Typical reach (10G) | 300 m (OM3) / 400 m (OM4) | 10 km+ (10GBASE-LR) |
| Relative cost | Cheaper optics | Cheaper per metre cable, pricier optics |
| Use | Inside buildings/data halls | Between buildings, campus backbone, WAN |
Fiber is immune to EMI and beats the 100 m copper limit; pick SMF for distance and future speed.
Copper UTP categories (100 m channel)
| Category | Rating | Notes |
|---|---|---|
| Cat5e | 1000BASE-T | Baseline for gigabit access runs |
| Cat6 | 1G, 10G to ~55 m | Better crosstalk margin than Cat5e |
| Cat6a | 10GBASE-T to 100 m | Thicker, often shielded |
Ethernet links are either point-to-point or shared media. A full-duplex link between a host and a switch port is point-to-point: only two transmitters exist, so collisions are impossible and both ends can send simultaneously. Legacy hubs create a shared media half-duplex segment where CSMA/CD arbitrates — one transmitter at a time, collisions normal. Modern switched networks are effectively all point-to-point full-duplex; a half-duplex reading on a switchport today is a fault indicator, not a design.
Sources
- Cisco CCNA 200-301 v1.1 Exam Topics (official PDF) — reviewed 2026-11-02
- IEEE 802.3 Ethernet Working Group — reviewed 2026-11-02
- Cisco — Interface and Hardware Component Command Reference — reviewed 2026-11-02
Targets CCNA 200-301 v1.1 objectives. Supplemental blocks are labeled beyond exam scope.