Chapter 13 / 13.8

13.8 REVISION QUESTIONS

1. Briefly describe the three basic transmission modes: simplex, half-duplex, and full-duplex. Give one practical example of each.

1. Explain the operational differences between simplex, half-duplex, and full-duplex transmission. For each, identify one advantage and one limitation.

1. Why does half-duplex communication require a channel coordination mechanism, whereas full-duplex communication does not require turn-taking? Does full-duplex eliminate the need for communication protocols? Explain.

1. A tactical radio network operates in half-duplex mode on a single frequency. Explain how hidden terminals and channel contention can limit network capacity.

1. Explain why multi-frequency HF broadcasting improves communication reliability without requiring the transmitter to know the receiver's location.

1. In what types of applications would simplex transmission be preferable to duplex, even if duplex operation were technically feasible?

1. Compare single-frequency and two-frequency half-duplex systems. What operational trade-offs do they introduce?

1. Explain the near-far problem in half-duplex radio systems. How might it be mitigated?

1. Briefly describe the four classical switching techniques: circuit switching, message switching, packet switching, and cell switching. Explain the types of traffic for which each is best suited.

1. Compare circuit switching and packet switching in terms of:

1. resource allocation;

1. delay characteristics;

1. bandwidth utilization; and

1. suitability for voice and data communications.

1. Briefly explain how facsimile (fax) transmission operates and why it was well suited to circuit-switched telephone networks.

1. Under what traffic conditions is circuit switching more efficient than packet switching? Under what conditions is it less efficient?

1. Explain why X.25 incorporated extensive error control within the network. Why did later packet-switching technologies largely eliminate these functions?

1. Compare X.25 and Frame Relay. Explain why Frame Relay achieved significantly higher throughput than X.25.

1. Explain why message switching is unsuitable for real-time voice communication but remains useful for delay-tolerant applications.

1. Explain how packet switching enables statistical multiplexing. How does this differ from conventional time-division multiplexing?

1. What is meant by a virtual circuit? How does it differ from both a physical circuit and a datagram-based packet service?

1. Why was Asynchronous Transfer Mode (ATM) based on fixed-length cells rather than variable-length packets? What problem was this intended to solve?

1. Explain how the evolution from X.25 to Frame Relay and ATM illustrates the movement of network intelligence from the network core toward the communicating devices.

1. Why does the choice of switching technique influence network scalability?

1. Modern IP networks are often described as combining connectionless and connection-oriented concepts. Explain why this statement is true.

1. Explain why packet size influences both transmission efficiency and communication delay.

1. Compare the principal xDSL technologies (ADSL, ADSL2+, VDSL2, G.fast, HDSL, and SDSL), indicating the applications for which each is most suitable.

1. Explain why traditional telephone networks limited voice bandwidth to approximately 3.4 kHz. Why is this not an inherent limitation of twisted-pair copper cable?

1. Compare Fiber-to-the-Home (FTTH) and DSL in terms of bandwidth scalability, deployment cost, operating distance, and long-term suitability.

1. Explain how Discrete Multitone (DMT) modulation exploits variations in signal-to-noise ratio across the available frequency spectrum.

1. Why does DSL performance decrease as the length of the copper subscriber loop increases?

1. Compare cable modem access and DSL in terms of dedicated versus shared bandwidth, achievable data rates, and network architecture.

1. Describe the operation of a cable broadband network. What roles are performed by the cable modem and the Cable Modem Termination System (CMTS)?

1. Explain why DOCSIS has continued to evolve even though many broadband providers are deploying fiber-optic access networks.

1. Compare fixed wireless access with cellular broadband. Why can fixed wireless systems often provide higher data rates than fully mobile users?

1. Explain the advantages and disadvantages of licensed and unlicensed spectrum for fixed wireless broadband access.

1. Describe how modern cellular broadband systems share radio spectrum efficiently among many users. In your answer, refer to OFDMA, adaptive modulation and coding, MIMO, and beamforming.

1. Explain how 5G differs from earlier generations of cellular systems and why it is suitable for both mobile broadband and fixed wireless access.

1. Compare geostationary (GEO), medium Earth orbit (MEO), and low Earth orbit (LEO) satellite broadband systems in terms of:

1. coverage;

1. propagation delay;

1. infrastructure complexity; and

1. typical applications.

1. Why do modern satellite broadband systems employ spot beams and frequency reuse? How do these techniques increase system capacity?

1. Explain why satellite broadband remains an important access technology despite the widespread deployment of terrestrial fiber-optic networks.

1. Compare FTTH, DSL, cable modem access, fixed wireless access, cellular broadband, and satellite broadband. Discuss the principal advantages, limitations, and typical applications of each technology.

1. A telecommunications provider must deliver broadband Internet access to:

1. a high-density apartment complex in a city;

1. a suburban housing estate;

1. a remote farming community;

1. a mining operation in an isolated region; and

1. a cargo ship operating in the Pacific Ocean.

1. Recommend the most appropriate access technology for each location and justify your choices.

1. Modern communication systems frequently combine fiber-optic, copper, coaxial, terrestrial radio, and satellite technologies within the same network. Explain why no single access technology is optimal for every application, and discuss the engineering trade-offs that influence the choice of access technology.