# Q5(b)(ii) · Ethernet physical media

Subject: Computer Networks

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/cn/#tee/papers/paper-2022-ai-final/q5bii

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Exact historical variant. Current-syllabus questions solved; excluded topics and source limitations stated.

### Q5(b)(ii). What physical media can Ethernet run over? Explain in detail. [5 marks]

### Answer

**Guided media** constrain signals to a physical path: twisted pair, coaxial cable and optical fiber. **Unguided media** carry electromagnetic waves through free space: radio, microwave and infrared. Wireless bandwidth and reach depend on frequency, power, antenna, obstacles and regulations; media names alone do not fix a speed.

Swipe across the diagram to read its labels ↔

![Transmission media: guided and unguided](https://deep-learning-study-room.vercel.app/cn/fig/tee-media.aff26cd0b5.svg)

Diagram: Transmission media: guided and unguided. Labels: Transmission media: guided and unguided | Transmission media: guided and unguided | Guided: a physical path | Twisted pair: electrical pairs. Coaxial: shielded conductor. Fiber: light through a protected core. | Unguided: waves in free space | Radio, terrestrial/satellite microwave, and infrared. Range and interference depend on the system. | Campus combination | Fiber backbone + copper access links + managed wireless mobility. Security and reliability need | configuration.

Transmission media classification.

| Medium | Two key characteristics | Limitations / use |
| --- | --- | --- |
| Twisted pair | Electrical signal; pairs twisted to reduce interference | Low-cost LAN access; distance/noise limits depend on category and design |
| Coaxial cable | Shielded central conductor; greater shielding than basic unshielded pair | Bulkier; cable broadband and legacy shared LANs |
| Optical fiber | Light in glass/plastic; high capacity with immunity to electromagnetic interference | Transceivers and careful splicing/bend control needed; backbone links |
| Radio waves | Wireless propagation; many bands support broad/non-line-of-sight coverage | Interference, shared spectrum and security configuration matter; Wi-Fi/mobile |
| Terrestrial microwave | Directional antennas; typically line of sight | Alignment and obstructions matter; point-to-point backhaul |
| Satellite microwave | Wide coverage through relay in space | Cost and latency depend strongly on orbit/system; remote connectivity |
| Infrared | Short-range light; usually blocked by walls | Limited coverage; short-range indoor/remote-control links |

#### Practical example

A university can connect buildings with fiber, desktops with twisted pair and mobile students with managed Wi-Fi. Satellite access is an option where suitable terrestrial links are unavailable.

**Yaad rakho:** Guided = cable path; unguided = free-space waves.

Transmission media are classified into guided media (twisted pair, coaxial cable, optical fiber) and unguided media (radio, microwave, infrared).

Optical fiber carries data as light in a core surrounded by cladding. It is a guided medium. Single-mode fiber supports one main propagation mode and is used for long/high-capacity links; multimode supports multiple modes and is often used over shorter distances.

| Advantages | Disadvantages / design costs |
| --- | --- |
| High data capacity and low attenuation over suitable links | Optical transceivers, connectors and splicing add cost/skill requirements |
| Immune to electromagnetic interference; no electrical crosstalk | Tight bends, dirty connectors and poor installation increase loss |
| Electrical isolation between buildings | Fiber is mechanically sensitive and requires appropriate protection |
| Harder to tap casually than an unprotected radio channel | It is not automatically confidential; encryption/access control remain necessary |

#### Practical example

A campus backbone can use fiber between buildings to avoid electrical interference and achieve high capacity. Installers still need to respect bend radius and test connectors.

**Yaad rakho:** Fiber light carry karta hai; immunity means no EMI, not no security risk.

Ethernet can use balanced twisted-pair copper (e.g.100BASE-TX/1000BASE-T), optical fiber (e.g.1000BASE-SX/LX), and historical coaxial cable (10BASE2/10BASE5). Twisted pair is economical for typical building runs; fiber supports longer reach and immunity to electromagnetic interference. The exact reach and rate depend on the Ethernet standard, not simply the word “fiber”.