The source of light for optic fibre transmission is _______.

The correct answer is C, 2022. Commercial 5G services began in India on 1 October 2022, when they were launched at the India Mobile Congress in New Delhi, following the spectrum auction held earlier that year in the 600 MHz, 700 MHz, 3300 MHz and 26 GHz bands among others. Option A is wrong because 2018 is the year of the National Digital Communications Policy, which set the goal of broadband for all but predates 5G service. Option B is wrong because 2020 saw trials and standards work, including the acceptance of the Indian 5Gi radio interface into the global standards, but no commercial service. Option D is wrong because 2024 is later than the launch; by then 5G had already spread to most districts. Fix the date 1 October 2022 together with the India Mobile Congress.

The correct answer is C, IMT-2020. The International Telecommunication Union names each generation of mobile telephony by a standard family, and 5G is IMT-2020, whose requirements include a peak downlink rate of 20 Gbps, a user experienced rate of 100 Mbps, one millisecond of air interface latency and a million connected devices in a square kilometre. Option A is wrong because IMT-2000 is 3G, the generation that first made mobile data and video calling practical. Option B is wrong because IMT-Advanced is 4G, met in practice by LTE and LTE-Advanced. Option D is wrong because IMT-2030 is the framework for 6G, which is still under development and is expected to appear commercially around 2030. The pattern is easy once seen: the number is the decade the generation was meant for.

The correct answer is A, Long Term Evolution. LTE is the radio technology through which 4G was delivered; the name was chosen because it was presented as the long-term evolution of the earlier 3G standards rather than a break with them. Its advanced version, LTE-Advanced, met the IMT-Advanced requirements that define true 4G. LTE made the network all-IP, so voice itself travels as packets, which is Voice over LTE or VoLTE. Option B is wrong because no standard uses the expansion Linear Transmission Encoding. Option C is wrong because Ethernet is a wired local area network technology and has nothing to do with the mobile radio standard. Option D is wrong because Local Transfer Exchange describes nothing in telecom; the exchange in a mobile network is the core, not an LTE.

The correct answer is C, 20 Gbps. Under IMT-2020 the peak downlink data rate for 5G is set at 20 gigabits a second, with 10 gigabits a second in the uplink; these are laboratory peaks under ideal conditions, not the speed a subscriber sees, and the separate target for the user experienced rate is 100 megabits a second downlink. Option A is wrong because 1 Gbps was the peak rate required of 4G under IMT-Advanced, which is exactly why it is offered as a distractor. Option B is the uplink figure for 5G, so it is right about the standard but wrong about the direction the question asks. Option D is wrong because 100 Gbps belongs to no mobile standard yet and is discussed only in the research literature on 6G and on fixed optical links.

The correct answer is D, circuit-switched voice bearer, which is not a 5G category at all; 5G is an all-IP system in which voice is carried as packets, and circuit switching belongs to the older 2G and 3G architecture. The three categories actually defined are given in the other options. Option A, enhanced mobile broadband, is the fast consumer internet with high data rates. Option B, ultra-reliable low-latency communication, is meant for driverless vehicles, factory automation and remote surgery, where a few milliseconds of delay matter. Option C, massive machine-type communication, is designed for very large numbers of cheap, low-power sensors, which is why the connection density target is a million devices per square kilometre. Remember the three by their initials, eMBB, URLLC and mMTC.