Physical Layer and Access Networks (Module 2)

50 question-and-answer style flashcards covering key concepts from Module 2: The Physical Layer, including guided and wireless media, PSTN, cellular generations, cable networks, and satellites.

What is the primary role of the Physical Layer in networking?

To transmit raw bits over a communication channel.

What are the two broad categories of transmission media?

Guided media and unguided (wireless) media.

Give three common examples of guided transmission media.

Twisted pair, coaxial cable, and fiber optics.

What humorous quote illustrates the bandwidth of persistent storage?

“Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway.”

Roughly how much data can Amazon’s Snowmobile transport?

Up to 100 PB (100 million GB).

Why are wires in twisted-pair cabling twisted together?

To reduce radiated signals and electromagnetic interference.

What does the acronym UTP stand for?

Unshielded Twisted Pair.

Which twisted-pair category supports Gigabit Ethernet (1 Gbps)?

Category 5e (Cat 5e).

Which connector is typically used with eight-wire twisted-pair cables?

RJ-45 connector.

Define a simplex link.

A link that allows transmission in only one fixed direction.

How does a half-duplex link operate?

Both directions are supported, but not simultaneously—senders take turns.

Give one advantage of coaxial cable over twisted pair.

Better shielding and more bandwidth over longer distances.

Why are household power lines considered poor for data transmission?

They are convenient but suffer high noise and attenuation.

What physical principle keeps light trapped inside a fiber-optic cable?

Total internal reflection.

Which fiber type has a 10 µm core and is used for long distances?

Single-mode fiber.

What is the theoretical capacity of the TAT-14 trans-Atlantic cable?

Approximately 3 Tbps.

List two security advantages of fiber over copper wires.

Harder to tap and lower signal leakage.

In wireless networking, what is an ISM band?

An unlicensed frequency band free for low-power devices such as Wi-Fi and Bluetooth.

Name two spread-spectrum techniques.

Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS).

State the relationship between wavelength (λ) and frequency (f).

λ × f = c, the speed of light.

Why do radio waves in the VLF/LF/MF bands follow the Earth's curvature?

They propagate as ground waves.

Above 100 MHz, why are microwaves suitable for point-to-point links?

They travel in nearly straight lines and can be narrowly focused.

What type of modulation does a typical TV remote use?

Infrared pulses around 38 kHz.

Give one major benefit of optical (laser) wireless transmission.

Very high bandwidth at low cost with relative security.

Mention one advantage of wireless networks compared with wired/fiber.

Easy and inexpensive to deploy, especially for mobility.

What is the basic idea behind multiplexing?

Combining multiple signals to share a single channel.

Name three common multiplexing techniques.

FDM, TDM, and CDMA.

What are the three major components of the Public Switched Telephone Network?

Local loops, trunks, and switching offices.

What is the function of the local loop in telephony?

It connects customer premises to the nearest switching office.

At what sampling rate and size is voice encoded in PCM for one call?

8-bit samples every 125 µs (64 kbps).

How many voice channels are carried in a traditional T1 line?

24 channels.

Which worldwide optical standard harmonizes high-speed carrier systems?

SONET/SDH.

In circuit switching, is call setup required?

Yes, a dedicated path is established before data flows.

Do packets in a packet-switched network always follow the same route?

No, each packet can take a different route.

What basic unit of mobile coverage reuses frequencies spatially?

A cell.

Which generation of mobile technology introduced GSM digital voice?

Second generation (2G).

How wide is a GSM radio channel and how many TDM slots does it carry?

200 kHz wide with eight time slots.

Which 3G system uses CDMA over 5 MHz channels?

UMTS (Universal Mobile Telecommunications System).

List two headline goals/features of 4G as defined by the ITU.

Pure IPv6 packet switching and up to 1 Gbps for stationary users (100 Mbps mobile).

Name one technology used in 5G to increase network capacity.

Massive MIMO, millimeter waves, or ultra-densification (any one).

What does HFC stand for in cable networks?

Hybrid Fiber-Coax.

Which standard defines the physical layer for cable modems?

DOCSIS (Data Over Cable Service Interface Specification).

What modulations are typically used for upstream/downstream in DOCSIS?

QPSK or QAM in assigned time slots.

In a cable system, what is the head-end?

Central point where signals are injected into the cable plant.

At what altitude do geostationary satellites orbit?

About 36,000 km above the equator.

What latency problem affects voice over GEO satellites?

About 250 ms round-trip delay causes noticeable lag.

Approximately how many satellites are in the Iridium LEO constellation?

66 satellites.

Which company operates the Starlink satellite Internet service?

SpaceX.

Give one advantage of satellites over fiber in remote areas.

Rapid deployment where terrestrial infrastructure is lacking.

When is a satellite niche market preferred over terrestrial networks?

When rapid deployment, global coverage, or broadcasting is essential.