This objective covers the physical layer of networking (Layer 1). It deals with how raw data is converted into light, radio waves, or electrical signals, and the physical hardware used to connect everything.
1. Wireless Media (Data Over the Air)
802.11 Standards (Wi-Fi)
Wi-Fi standards dictate how wireless local area networks operate. The exam tests your knowledge of frequencies and capabilities:
- 802.11b: Older standard operating strictly at 2.4 GHz.
- 802.11g: Improved speed over 802.11b but still operates strictly at 2.4 GHz.
- 802.11n (Wi-Fi 4): Introduced MIMO (Multiple Input, Multiple Output). Operates at both 2.4 GHz and 5 GHz.
- 802.11ac (Wi-Fi 5): Operates strictly at 5 GHz for high-speed local data.
- 802.11ax (Wi-Fi 6/6E): Highly efficient. Wi-Fi 6 covers 2.4 GHz and 5 GHz, while Wi-Fi 6E extends explicitly into the clean 6 GHz band.
Cellular & Satellite
- Cellular: Uses localized cell towers to connect mobile devices over broad geographic areas (e.g., 4G LTE, 5G).
- Satellite: Connects remote sites directly to satellites in space.
- GEO (Geostationary Orbit): High-altitude satellites that stay over one spot on Earth. They offer wide coverage but suffer from high latency due to the immense distance the signal must travel.
- LEO (Low Earth Orbit): Much closer to Earth. They provide lower latency and faster speeds but require a shifting constellation of multiple satellites to maintain coverage.
2. Wired Media (Data Over Cables)
802.3 Standards (Ethernet)
These standards define how fast data moves over specific cable lengths.
- 10BASE-T: 10 Mbps over copper twisted pair.
- 100BASE-TX: Fast Ethernet (100 Mbps) over copper twisted pair.
- 1000BASE-T: Gigabit Ethernet (1 Gbps) over copper twisted pair.
- 10GBASE-T: 10 Gigabit Ethernet (10 Gbps) over copper twisted pair.
Fiber Optic Cables: Single-mode vs. Multimode
Fiber optics sends data as pulses of light through a glass core.
- Single-mode Fiber (SMF): Has a very narrow core. It uses a single laser to shoot light straight down the center. Because the light doesn’t bounce around, there is very little signal degradation.
- Usage: Long distances (miles/kilometers), such as campus backbones or WAN connections.
- Multimode Fiber (MMF): Has a wider core. It uses cheaper LED lights that bounce around the core at multiple angles (“modes”). This causes signal degradation over long distances.
- Usage: Short distances (up to 550 meters), typically used inside a single server room or data center.
Specialized Cabling
- Direct Attach Copper (DAC) / Twinaxial Cable: A specialized copper cable with transceiver modules permanently attached to both ends. It is incredibly fast, cheap, and energy-efficient.
- Usage: Connecting a server directly to a switch sitting in the same rack (distances under 7–10 meters).
- Coaxial Cable: A single copper core surrounded by a shielding layer. Used primarily by cable TV and internet service providers (via DOCSIS standards).
- Plenum vs. Non-Plenum:
- Plenum-rated: Built with fire-resistant plastics that do not emit toxic smoke when burning. Mandatory for use in air-handling spaces (such as drop ceilings or raised floors) where HVAC systems circulate air.
- Non-Plenum (PVC): Standard cable jacket. Cheaper, but it emits toxic smoke when burned. Used in standard walls and exposed areas.
3. Transceivers & Form Factors
A transceiver is a hot-swappable component that plugs into a switch port to convert a switch’s electrical signals into fiber optic light or copper signals.
Protocols
- Ethernet: The standard protocol used for general local area networking.
- Fibre Channel (FC): A specialized, ultra-high-speed protocol used strictly to connect servers to a Storage Area Network (SAN).
Form Factors (Sizes)
- SFP (Small Form-factor Pluggable): Standard slot size supporting up to 1 Gbps.
- SFP+: The same physical size as an SFP, but supports speeds up to 10 Gbps.
- QSFP (Quad SFP): A wider transceiver that combines four data channels into a single module to support higher speeds, such as 40 Gbps.
- QSFP+ / QSFP28: Upgraded versions of the QSFP supporting speeds up to 100 Gbps and beyond.
4. Connector Types (The Plugs)
Fiber Connectors
- SC (Subscriber Connector): A square, plastic connector that uses a simple Push-Pull mechanism to lock into place.
- LC (Local Connector): A small-form-factor connector with a plastic locking tab (similar to an Ethernet plug). It is highly popular because its small size allows for high-density packing on switches.
- ST (Straight Tip): An older, round metal connector that connects using a Bayonet twist-lock mechanism (like a camera lens).
- MPO (Multi-fiber Push On): A wide ribbon-style connector that connects a bundle of up to 12 or 24 fiber strands simultaneously. Commonly used with QSFP transceivers in high-speed enterprise links.
Copper & Coaxial Connectors
- RJ11: Small plastic connector used for traditional phone lines and DSL modems (4–6 pins).
- RJ45: Standard 8-pin plastic connector used to crimp onto Ethernet cables.
- F-Type: A threaded screw-on metal connector used on the end of coaxial cables for cable modems and television lines.
Key Exam Study Matrix
| Component | Category | Key Identifying Phrase for the Exam |
| Plenum | Cable Jacket | Fire-retardant; mandatory for drop ceilings and air spaces. |
| LC | Fiber Plug | Small form-factor; push-pull tab; high-density environments. |
| ST | Fiber Plug | Twist-lock; bayonet-style connection. |
| Single-mode | Fiber Cable | Long-distance; uses a laser light source. |
| QSFP | Transceiver | “Quad” layout used for high-bandwidth applications (40/100G). |
| F-Type | Copper Plug | Screw-on metal cap; used with coaxial cables. |