Copper twisted-pair (UTP), fiber (single-mode and multi-mode), serial, and wireless. This chapter covers connector types, distance and speed limits, and how to pick the right media for the job.
Twisted-pair Ethernet uses RJ-45 connectors. Two pin-outs exist — straight-through (PC-to-switch) and crossover (switch-to-switch on legacy gear). Modern devices auto-detect with Auto-MDIX so the distinction barely matters in practice, but it is still worth knowing.
| Category | Speed | Distance | Typical use |
|---|---|---|---|
| Cat5e | 1 Gbps | 100 m | Office desks (legacy) |
| Cat6 | 10 Gbps | 55 m | Office desks (modern) |
| Cat6a | 10 Gbps | 100 m | 10G to the desktop |
| Cat7/8 | 25–40 Gbps | 30 m | Data center top-of-rack |
Multi-mode fiber (MMF) has a wider core and uses LED or VCSEL light sources. It is cheaper, easier to terminate, and is the default inside a building or data center. Distances are typically 300–550 m at 10 Gbps.
Single-mode fiber (SMF) has a much thinner core and uses laser light. It costs more but supports tens of kilometers between buildings or campuses. SMF is your only realistic option for inter-site links over a few hundred meters.
1 more section in this chapter, plus a 2-question quiz.
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