Copper, Fiber, Coax, and DAC Media
Key Takeaways
- Twisted-pair copper Ethernet is limited to 100 m total channel (90 m horizontal plus 10 m patch) and is the default for Power over Ethernet endpoints.
- Multimode fiber (OM3/OM4/OM5, orange/aqua/lime jackets) carries 10G to ~300-550 m; single-mode (OS2, yellow jacket) reaches tens of kilometers.
- Coax in Network+ means RG-6/RG-59 broadband with F-type and legacy 10BASE2/10BASE5 bus with BNC; it is a shared or provider-handoff clue.
- Direct attach copper (DAC) is a fixed factory-terminated SFP/QSFP assembly for ~1-7 m intra-rack links and needs no separate optics.
- Match the medium to the dominant constraint in the scenario: distance, EMI immunity, electrical isolation, PoE, or cost.
How Network+ Frames Media Questions
N10-009 media items describe one dominant physical constraint: distance, speed, electromagnetic interference (EMI), cost, Power over Ethernet (PoE), or an existing connector. Identify the constraint first, then pick the medium. The exam is 90 questions in 90 minutes with a passing score of 720 on a 100-900 scale, and Domain 1 (Networking Concepts) is 23% of that weight, so media recall is heavily tested.
| Medium | Best fit | Hard limit / strength | Watch for |
|---|---|---|---|
| Twisted-pair copper | Workstations, APs, phones, cameras | 100 m channel, supports PoE | EMI, category mismatch |
| Multimode fiber (MMF) | Building/data-center optical runs | EMI-immune, ~300-550 m at 10G | Modal dispersion, shorter than SMF |
| Single-mode fiber (SMF) | Campus, ISP, long haul | Tens of km, highest bandwidth | Pricier optics, dirty/bent end faces |
| Coaxial cable | Broadband, RF, CCTV, legacy bus | Shielded RF carrier | Shared medium or ISP-handoff clue |
| Direct attach copper (DAC) | Intra-rack switch-to-server | Cheap, low-latency, no optics | Fixed 1-7 m length only |
Twisted-Pair Copper
Balanced twisted pairs cancel interference. The classic clue is an endpoint inside an office that also needs power, because PoE (802.3af 15.4 W), PoE+ (802.3at 30 W), and PoE++/4PPoE (802.3bt up to ~71-100 W) all ride twisted pair. The total Ethernet channel is 100 meters (about 328 feet): 90 m of solid horizontal cable plus 10 m of stranded patch cords. Exceed it and you see late collisions, CRC errors, or no link.
| Category | Rated speed / bandwidth | Exam association |
|---|---|---|
| Cat 5e | 1 GbE, 100 MHz | Older office access |
| Cat 6 | 10 GbE to 55 m, 250 MHz | Mixed 1G/10G drops |
| Cat 6a | 10 GbE to 100 m, 500 MHz | 10G horizontal standard, low alien crosstalk |
| Cat 7 / 7a | Shielded, 600-1000 MHz | High-EMI niche, GG45/TERA |
| Cat 8 | 25/40 GbE to 30 m | Data-center top-of-rack only |
Cat 6 carries 10G only to ~55 m; for a full 100 m 10G drop you need Cat 6a. Shielded twisted pair (STP/F/UTP) helps near motors or generators but must be bonded and grounded at both ends, or the shield becomes an antenna and worsens the fault. Standard office wiring is unshielded twisted pair (UTP).
Fiber Media
Fiber carries light, so it is immune to EMI and creates no copper path between buildings (no shared ground, no lightning conduction). That makes it the answer whenever the scenario mentions electrical isolation, long distance, or an electrically noisy environment.
| Fiber grade | Core / type | Typical 10G reach | Jacket color clue |
|---|---|---|---|
| OM1 | 62.5 um MMF | ~33 m at 10G | Orange |
| OM3 | 50 um laser-optimized MMF | ~300 m at 10G | Aqua |
| OM4 | 50 um MMF | ~400 m at 10G | Aqua/violet |
| OM5 | wideband MMF | ~400 m, SWDM | Lime green |
| OS2 | 9 um single-mode | 10-40+ km | Yellow |
Key numbers: 10GBASE-SR over OM3 reaches ~300 m; over OM4 ~400 m. 10GBASE-LR over OS2 single-mode reaches ~10 km, and 10GBASE-ER ~40 km. Common faults are excessive bend radius, dirty end faces, mismatched optics, and Tx/Rx polarity reversal. In a PBQ, inspect and clean end faces, confirm the transceiver matches the fiber type, verify polarity, and check light/dBm levels with a meter when available.
Coax and DAC
Coaxial cable has a center conductor, dielectric, braided shield, and jacket. Network+ coax appears as broadband RG-6/RG-59 with screw-on F-type (cable modems, DOCSIS, antenna/RF, some CCTV) and legacy bus Ethernet 10BASE2 (Thinnet) / 10BASE5 (Thicknet) with BNC. Coax is a shared-medium or provider-handoff clue.
Direct attach copper (DAC) is different: a factory-terminated twinaxial assembly with SFP+/SFP28/QSFP ends fused to the cable. It needs no separate optics, runs ~1-7 m, and is the cheapest way to do 10/25/40/100G inside one rack.
| Requirement | Media answer | Why |
|---|---|---|
| Power a ceiling AP from the switch | Twisted-pair copper | PoE rides copper |
| Link two buildings across campus | Single-mode fiber | Distance + electrical isolation |
| Connect adjacent top-of-rack switches | DAC | Short, cheap, fast |
| Cable modem to provider wiring | Coax (F-type) | Broadband RF handoff |
| Run through a noisy industrial bay | Fiber | EMI immunity |
| 10G optical run inside one data center | Multimode fiber | Cost-effective short reach |
Worked Scenarios and Selection Drill
Scenario 1: A warehouse camera drops link every time large motors start, on a long copper run beside power conduit. Do not just "replace the cable." The root constraints are EMI and distance. Best design: fiber for the long noisy segment, copper only for the final PoE camera drop via a media converter or PoE switch near the endpoint.
Scenario 2: A server team wants a low-cost 25 GbE link between a server and a top-of-rack switch 2 m away. DAC wins: it is within DAC's ~1-7 m range, far cheaper than two SFP28 optics plus a fiber patch, and adds minimal latency.
| If the question says... | Think... |
|---|---|
| Needs PoE | Twisted-pair copper |
| Long distance between buildings | Single-mode fiber |
| 25/40/100G inside the same rack | DAC |
| Existing cable-TV provider handoff | Coax / F-type |
| EMI or electrical isolation required | Fiber |
| Short 10G optical run in a data center | Multimode fiber |
| 10G drop at full 100 m on copper | Cat 6a |
Common trap: choosing Cat 6 for a 100 m 10G run (it only reaches ~55 m at 10G), or choosing coax for a modern LAN uplink when the real clue was a cable-broadband handoff.
A company needs a short, low-cost 25 GbE connection between a server and a top-of-rack switch about 2 meters away in the same rack. Which media is the best fit?
A technician must run a full 100-meter horizontal copper drop that supports 10 GbE. Which cable category is required?
Which medium is usually preferred for a long campus link between two buildings because it avoids shared electrical grounding and supports many kilometers?