Transmission Media

Transmission media and Transceivers

802.11 Standards (Wi-Fi)

These are the IEEE Wi-Fi standards — they define how wireless communication happens over the air.

Multiple Input, Multiple Output(MIMO) which uses multiple antennas on both the transmitter (router/AP) and receiver (laptop/phone) to send and receive separate data streams at the same time on the same frequency.

Multi-User MIMO (MU-MIMO) allows the access point to communicate with multiple clients simultaneously. Before MU-MIMO, the AP could only talk to one device at a time—just very quickly switching between them. With MU-MIMO,the AP can send different streams to different users at once.

Beamforming A technique where the AP focuses its radio signal toward a specific device instead of broadcasting equally in all directions.

Orthogonal Frequency Division Multiple Access (OFDMA) A channel-sharing method introduced in 802.11ax (Wi-Fi 6) that divides a Wi-Fi channel into smaller sub-channels called Resource Units (RUs) so multiple devices can transmit simultaneously instead of waiting for their turn. How it works:Each channel (e.g., 20 MHz) is divided into many small sub-carriers, each sub-carrier is assigned to a different client/device.

Cellular Networks

Used by smartphones and some IoT devices to connect to the internet via cell towers.

Satellite Communication

Used where there's no cellular or fiber coverage — rural areas, ships, aircraft. Offers usable speeds (e.g. 100 Mbps down / 5 Mbps up).

Major Disadvantages & Challenges:

• Cost and Complexity: It is more expensive and complex to implement than traditional internet options.
• Latency (Delay): ~500 ms round-trip (250 ms up, 250 ms down).
• Line-of-Sight Requirement: Requires a clear, unobstructed view of the satellite. Any blockage (by trees, buildings, etc.) can degrade performance or cause a complete loss of connection.

802.3 Standards — Ethernet Family

The IEEE 802.3 standard defines wired Ethernet — how devices communicate over cables.

Each version specifies speed, medium, and maximum distance.

Single-Mode vs. Multimode Fiber

Direct Attach Copper (DAC) Cable

A DAC is a fixed-length cable that has Twinax cables with transceivers permanently attached to both ends.

Used to directly connect network devices like switches and servers without needing separate transceivers.

Twinaxial (Twinax) Cable

This refers to the physical construction of the cable. It's a type of coaxial cable with two inner conductors (instead of one) inside a single shield.

Coaxial Cable

Copper cable with one central conductor, surrounded by insulation, shield, and outer jacket — minimizes interference.

Cable Speeds (Common Copper Types)

The Plenum and Cable Safety

The plenum is the open space between a drop ceiling and the actual building ceiling, used to route cables, pipes, and ductwork for air circulation.

Plenum-Rated vs. Non-Plenum Cable

• Standard Cable (PVC): Typically has a jacket made of Polyvinyl Chloride (PVC), which produces thick, toxic smoke when burned.
• Plenum-Rated Cable: Has a special jacket made of Fluorinated Ethylene Polymer (FEP) or low-smoke PVC. It is fire-retardant and emits much less smoke and fewer toxic fumes.

Plenum-rated cable is safer but is often less flexible and more expensive than standard PVC cable, making it slightly more challenging to install.

Transceivers

A transceiver (transmitter + receiver) converts electrical signals ↔ optical or electrical signals to send data across a cable or fiber.

Instead of a network switch having fixed, unchangeable ports, transceivers let you customize each port. Every port can be different. You are not locked into one type of connection for the entire device.

• Port 1: Could be for a local computer (using a copper transceiver).

• Port 2: Could be for a long-distance link to another building (using a fiber transceiver).

• Port 3: Could be for a high-speed server (using a 10-gig transceiver).

FORM FACTORS (Transceiver Types)

QSFP was developed to meet the demand for higher bandwidth density. Instead of using four separate SFP ports to get 4 x 1 Gbps = 4 Gbps, you can use a single QSFP port to achieve the same (or much higher) total speed, saving space and power.

CONNECTOR TYPES (Physical Cable Ends)

Fiber Connectors

Copper Connectors