23CIT3015SEM2 Past Paper PDF

Answer sheet for past paper 23CIT3015SEM2 B. Compare bipolar return to zero (RZ) and bipolar non return to zero code in relation to. Bandwidth: Bipolar RZ requires more bandwidth due to its additional signal transitions and narrower pulse widths, while Bipolar NRZ is more bandwidth-efficient with f...

Answer sheet for past paper 23CIT3015SEM2 B. Compare bipolar return to zero (RZ) and bipolar non return to zero code in relation to. Bandwidth: Bipolar RZ requires more bandwidth due to its additional signal transitions and narrower pulse widths, while Bipolar NRZ is more bandwidth-efficient with fewer signal changes and wider pulses.. Error Detection: Bipolar NRZ has limited error detection capabilities as it lacks inherent self- synchronization, whereas Bipolar RZ provides better error detection due to more frequent signal transitions that make anomalies more detectable.. Clock Recovery: Bipolar RZ offers superior clock recovery because the signal returns to zero after each bit period, providing consistent timing references, while Bipolar NRZ struggles with clock recovery during long sequences of identical bits due to fewer signal transitions. C. Why is synchronization more important in a digital system, than in an analogue system In a digital system, precise synchronization is crucial because even minor timing errors can cause complete misinterpretation of discrete signal states, whereas analogue systems can more gracefully accommodate signal variations without catastrophic information loss. D. How does Sky propagation differ from line of sight propagation? [4 marks] Answer: Sky propagation uses the ionosphere to reflect radio waves, allowing long-distance communication beyond the horizon, typically in the HF frequency range. In contrast, line of sight propagation involves direct travel of radio waves between the transmitter and receiver, with its range limited by obstacles and the Earth's curvature, typically used in VHF and UHF frequencies. Sky propagation is ideal for distant, over-the-horizon communication, while line of sight is used for clearer, shorter-range communication. E. What is the bandwidth of a signal that can be decomposed into five sine waves with frequencies at 0, 20, 50, 100, and 200hz? All the amplitudes are the same. Draw the bandwidth [6 Marks] Answer: The bandwidth is the difference between the highest frequency and lowest frequency in this case the highest frequency is 200HZ and the lowest frequency is 0HZ so 200 – 0 = 200HZ So the bandwidth of the signal is 200hz  0 20 50 100 200 F. Signal with 200 milliwatts power passes through 10 devices, each with an average noise of 2 microwatts. Calculate the SNR and SNRdB [6 Marks] Psignal = 200milliwatts = 200 x 10-3W = 0.2 W Pnoise = 2 microwatt = 2 x 10-6W = 0.000002W Ptotal noise = 10 x 2microwatt = 20microwatt = 20x 10-6W = 0.00002 W SNR SNR= Psignal / Ptotal noise =0.2/ 0.00002=10,000 SNR Db = 10 x log10(10,000) = 10 x 4 or 10^4 = 40db G. state the mathematical relationship between velocity, frequency and wavelength [4 marks] mathematically related through the fundamental equation v = f.λ, which holds true for all wave types. This equation states that a wave's velocity equals its frequency multiplied by its wavelength, or conversely, can be rearranged to calculate any of these parameters when the other two are known. The relationship demonstrates that as frequency increases, wavelength decreases proportionally (or vice versa) when the wave's velocity remains constant, making it a crucial principle in understanding wave propagation across various mediums like sound, light, and electromagnetic radiation. H. A transmission system has a period of 1 nanosecond. Calculate the wavelength of the system in meters, if the velocity of light is 3 x 108 m/s [6 marks] V = f. λ T = 1 nanoseconds =1 x 10-9 F = 1/T 1/ 1 x 10-9 = F= 1 x 109 Rearrange the formula λ = v/f = 3 x 108 / 1 x 109 = 0.3 m or 30 cm The wavelength of the system is 0.3 meters (or 30 centimeters). I. Distinguish between data rate and signal data Data rate represents the volume of information transmitted per unit time (measured in bits per second), while signal data describes the physical characteristics of the signal used to carry that information, including its frequency, amplitude, and modulation technique. J. Explain why diphase (or Machester) coding is suited for clock recovery where long sequence of zeros may occur. In Manchester (diphase) coding, every bit is represented by a transition in the middle of the bit period, ensuring that there is always a signal change regardless of the data sequence. This guaranteed transition at each bit interval allows for reliable clock recovery, preventing synchronization loss during long sequences of zeros where other encoding methods might maintain a constant signal level and cause the receiver's clock to drift. SECTION B A. Briefly describe the operation of the OSI model and the services provided by data link [6 Marks] The OSI model has 7 layers Each layer serves a specific purpose and provides services to the layer above it while receiving services from the layer below. The layers of the OSI model, from bottom to top, are: Physical Layer, Data Link Layer, Network Layer, Transport Layer, Session Layer, Presentation Layer, and Application Layer. The Data Link Layer (Layer 2) provides critical services that ensure reliable transmission of data between directly connected nodes in a network. Its primary functions include framing, which breaks network layer packets into frames, physical addressing by adding MAC addresses, error detection to identify transmission errors, and flow control to manage data transmission rates. The layer ensures that data is transmitted reliably between two directly connected points, handling the immediate point-to-point communication in the network. B. Define piggybacking and its usefulness, and provide illustrations where necessary [7 Marks] Piggybacking is a communication technique in data transmission where acknowledgment (ACK) signals are combined with new data packets, reducing network overhead and improving communication efficiency. Instead of sending separate acknowledgment packets, the receiver incorporates the acknowledgment into the next data frame it sends back to the sender, thus "piggy-backing" the acknowledgment onto a data transmission. C. Discuss the relative advantage and disadvantages of sliding window go back N in comparison with sliding window selective. the sliding window Go-Back-N (GBN) and Selective Repeat (SR) protocols represent two distinct approaches to reliable data transmission, each with its own set of strengths and weaknesses. Go-Back-N operates on a simpler principle where if a packet is lost or corrupted, the sender retransmits not just the lost packet but the entire window of subsequent packets, which can be inefficient but computationally less complex. In contrast, Selective Repeat allows for more granular error recovery by retransmitting only the specific lost or corrupted packets, thereby reducing unnecessary retransmissions and potentially improving overall network efficiency. The GBN approach requires less buffer space at both the sender and receiver, as only the most recent window needs to be maintained, while SR demands more significant buffer resources to selectively retain and potentially reorder out-of-sequence packets. However, this complexity in SR provides better throughput, especially in networks with higher packet loss rates, as it minimizes redundant transmission of already correctly received packets. C. State clearly how the error correction is controlled by stop-wait ARQ (Stop-and-Wait ARQ) is a fundamental error control protocol that manages data transmission reliability through a simple yet methodical approach. In this protocol, the sender transmits a single data frame and then waits for an acknowledgment (ACK) from the receiver before sending the next frame. If the sender does not receive an ACK within a specified timeout period, it assumes the frame was lost or corrupted and retransmits the same frame. The error correction mechanism is controlled by a sequential process where each frame is assigned a sequence number (typically alternating between 0 and 1) to help the receiver identify duplicate transmissions and ensure proper sequence. D. Draw the frame format of a frame in a character- oriented protocol of data link control Flag Header 011001 101000 … 011001 001010 Trailer Flag E, Using the concept of taxonomy of protocol, discuss the protocol use in data link layer  In the taxonomy of network protocols, the data link layer plays a crucial role in managing communication between directly connected network nodes. The data link layer protocols are categorized into several key types, each addressing specific network communication challenges. Framing protocols like High-Level Data Link Control (HDLC) and its derivatives such as Point-to-Point Protocol (PPP) provide fundamental mechanism for encapsulating data into frames, adding control information, and managing the basic unit of data transmission. Error control protocols are critical in this layer, with approaches ranging from simple parity checks to more sophisticated cyclic redundancy check (CRC) methods. Protocols like Automatic Repeat reQuest (ARQ) variants - including Stop-and-Wait, Go-Back-N, and Selective Repeat - implement different strategies for detecting and correcting transmission errors. Flow control mechanisms are equally important, with protocols like Sliding Window protocol managing the rate of data transmission to prevent overwhelming the receiver. Media Access Control (MAC) protocols become particularly significant in shared media environments, with approaches like Carrier Sense Multiple Access (CSMA) and its variants (CSMA/CD, CSMA/CA) solving the challenges of multiple nodes accessing a single communication channel. Ethernet, one of the most prevalent data link layer protocols, exemplifies these principles by providing a standardized approach to local area network (LAN) communication. These protocols work in concert to ensure reliable, efficient, and error-free data transmission at the link layer, managing everything from basic frame delivery to complex network access scenarios. SECTION C A. What is multiplexing? Multiplexing is a technique used to combine multiple signals or data streams into a single transmission medium, such as a cable, fiber optic line, or radio frequency channel. Notes Two types of Multiplexing FDM – Frequency division multiplexing TDM – time division multiplexing B. Describe the goal of multiplexing The primary goal of multiplexing is to optimize the use of a communication channel by allowing multiple signals or data streams to share the same medium simultaneously. This reduces infrastructure costs, improves bandwidth efficiency, and ensures effective resource utilization. By separating signals at the receiver, multiplexing ensures that each stream reaches its intended destination without interference. C. Explain the concept of TDM Time Division Multiplexing (TDM) is a technique that divides a communication channel into fixed time slots, with each slot assigned to a specific signal. Signals take turns using the channel, ensuring no overlap. There are two types: Synchronous TDM, where slots are pre- assigned regardless of data presence, and Asynchronous TDM, where slots are dynamically allocated based on demand. TDM is commonly used in digital telephony and data transmission. D. Explain with illustration state the principles of : multilevel multiplexing Multilevel multiplexing combines signals from multiple sources into a higher-level signal when individual sources do not fully utilize the bandwidth of the transmission medium. Multiple lower-bandwidth signals are grouped together to form a composite signal, which is then transmitted over a shared channel. Multiple slot multiplexing In multiple slot multiplexing, a single source uses more than one time slot per cycle in a Time Division Multiplexing (TDM) system. This is employed when a source has higher bandwidth or data rate requirements that exceed what a single time slot can accommodate.  pulse stuffing Pulse stuffing is used to synchronize data streams with slightly different data rates. Extra bits, or "stuffed pulses," are added to slower streams to match the speed of the fastest stream, ensuring proper alignment during multiplexing. E. With a well labeled diagram, state the concept of interleaving using TDM Interleaving in TDM is the process of dividing a communication channel into fixed time slots and arranging the data from multiple sources in a sequential, alternating manner within those slots. Each source sends its data in turn, and the receiver reconstructs the original streams by separating them based on their assigned time slots.  F. A multiplexer combines four 200kbps channels using a time slot of 2 bits. Show the output with four arbitrary inputs. What is the time frame rate? What is the time frame duration? What is the bit rate? What is the bit rate duration? Number of channels: 4 Each channel bit rate: 200 kbps Time slot per channel: 2 bits Calculate the time frame rate Time Frame Rate= Bit Rate of One Channel / Bits in a Frame (per channel) Time frame rate = bit rate of one channel / bit per channel per frame = 200kbps/2bits = 100 frames Calculate the time frame duration Time frame duration = 1/time frame rate 1/100 =0.01 seconds per frame Calculate the output bit rate Output Bit Rate=Number of Channels×Bit Rate of One Channel Output Bit Rate=4×200kbps=800kbps Calculate the bit duration bit duration = 1/output bit rate 1/800kbps = 0.00125 seconds per bit Summary of Results Output Bit Stream: 10011100 Time Frame Rate: 100 frames/second Time Frame Duration: 0.01 μs Output Bit Rate: 800 kbps Bit Duration: 0.00125 seconds G. What is spreading Spreading involves taking a narrowband signal and expanding it over a much wider bandwidth. This is done by multiplying the original signal with a spreading code (also called a pseudo- random code or sequence) that has a much higher frequency than the original signal. The two main types of spreading techniques are AND THIS IS HOW IT IS ACHIEVED: Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS) Spreading is achieved using techniques that expand a signal's bandwidth to enhance its robustness and security. One common method is Direct Sequence Spread Spectrum (DSSS), where the data signal is multiplied by a high-frequency pseudo-random code, causing the signal to occupy a much larger bandwidth than its original. This ensures resistance to interference and noise. Another method is Frequency Hopping Spread Spectrum (FHSS), where the signal's carrier frequency rapidly hops across different frequencies according to a pseudo-random sequence. This dynamic frequency change makes the signal resilient to jamming and interception while efficiently utilizing the frequency spectrum. Both techniques are foundational in modern communication systems for achieving reliable and secure transmission. H. Why is Spreading? Spreading is used in digital communication to enhance signal robustness, security, and efficiency. By distributing the signal over a wide frequency band, it becomes less vulnerable to interference and jamming, as narrowband disturbances impact only a small part of the spread signal. This technique also enables multiple users to share the same frequency band simultaneously, with unique spreading codes distinguishing their signals, as seen in CDMA systems. The pseudo-random spreading codes enhance security by making the signal difficult to intercept without the proper code. Spreading mitigates multipath effects by allowing receivers to resolve delayed signal components, improving quality. Additionally, it reduces the power spectral density, minimizing interference with other systems and adhering to regulatory standards. The resulting processing gain increases resistance to noise and errors, ensuring reliable communication even in challenging environments.