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Cabling & Physical (L1)
The media everything rides on — copper categories, fiber, connectors, PoE budgets and transceivers.
// copper (twisted pair)
| Category | Speed | Max length | Notes |
|---|
| Cat5e | 1 Gbps | 100 m | — |
| Cat6 | 1 Gbps (10G @55m) | 100 m | — |
| Cat6a | 10 Gbps | 100 m | shielded options |
| Cat7 | 10 Gbps | 100 m | fully shielded |
| Cat8 | 25–40 Gbps | 30 m | data center |
// fiber
| Single-mode (SMF) | Long distance (km), laser, yellow jacket |
| Multi-mode (MMF) | Short reach (<550 m), LED, aqua/orange |
// PoE standards
| 802.3af (PoE) | 15.4 W |
| 802.3at (PoE+) | 30 W |
| 802.3bt (PoE++) | 60–100 W |
// transceivers
| SFP | 1 Gbps |
| SFP+ | 10 Gbps |
| SFP28 | 25 Gbps |
| QSFP+ | 40 Gbps |
| QSFP28 | 100 Gbps |
// optical connectors
| LC | Local Connector — small form, very common |
| SC | Subscriber Connector — push/pull |
| ST | Straight Tip — bayonet twist-lock |
| MT-RJ | Duplex, compact |
// copper / serial connectors
| RJ-45 | 8P8C — Ethernet |
| RJ-11 | Phone / DSL |
| RJ-21 | 25-pair telco (Amphenol) |
| DE-9 (DB-9) | Serial console |
| DB-60 | Cisco serial WAN |
// T568A / T568B pinout
| Pin | T568A | T568B |
|---|
| 1 | White-Green | White-Orange |
| 2 | Green | Orange |
| 3 | White-Orange | White-Green |
| 4 | Blue | Blue |
| 5 | White-Blue | White-Blue |
| 6 | Orange | Green |
| 7 | White-Brown | White-Brown |
| 8 | Brown | Brown |
// cable types
| Straight-through | Same standard both ends — host ↔ switch/router |
| Crossover | A on one end, B on the other — like ↔ like (switch ↔ switch) |
| Rollover | Reversed — console (RJ45 ↔ DB9) for CLI access |
// facts
- T568A vs T568B = wiring pinout (pick one, be consistent)
- Straight-through (host↔switch) vs crossover (like↔like); auto-MDIX handles it
- Copper UTP max 100 m per run
- Fiber is immune to EMI and spans long distance
- Connectors: RJ45 (copper) · LC / SC / ST / MTP (fiber)