A collision domain is, as the name implies, the part of a network where packet collisions can occur. A collision occurs when two devices send a packet at the same time on the shared network segment.
Bridges and routers isolate collision.
A router not only breaks collision domains but also breaks broadcast domains, which means it is both collisions as well as broadcast domain separators. A router creates a connection between two networks.
Bridges area is a Layer 2 device that separates collision domains by determining what MAC addresses are on each side of the bridge and only passing traffic if the destination address is on the other side of the bridge.
32. In time-division multiplexing, there are 8000 samples for a digital signal-0 channel that uses 8 kHz sample rate and 8 bit PCM code. The line speed will be:
56 kbps
64 kbps
76 kbps
84 kbps
Answer.2. 64 kbps
Explanation
Given: fs = 8 kHz, n = 8 bits
The number of signals multiplexed is not given, so the given TDM is normal PCM only, where only one signal is transmitted.
∴ m = 1
Line speed (R = mnfs
Rb = 8 × 8 kHz
Line speed (R = 64 kbps
33. Minimum packet size increases as
Speed increases
Distance increases
Speed & Distance increases
None of the mentioned
Answer.3. Speed & Distance increases
Explanation
A network packet is a small amount of data sent over Transmission Control Protocol/Internet Protocol (TCP/IP) networks.
The internet’s transmission control protocol (TCP) uses the MTU to determine the maximum size of each packet in any transmission.
As speed and distance go up, minimum packet size also goes up.
34. The circuit used to regenerate clock pulses from the transmitted PAM signals is called ____
Clock demodulator circuits
Timer circuits
Clock receiving circuits
Clock recovery circuits
Answer.4. Clock recovery circuits
Explanation
A clock recovery circuit supplies timing to a phase-locked loop (PLL), which in turn controls a clock for the recovered upstream information. To recover the sampling clock, the receiver needs a reference to a clock of approximately the same frequency.
To generate the recovered clock, the receiver needs to phase align the reference clock to the transitions on the incoming data stream.
Instead of using a free-running clock oscillator set to the identical frequency of the transmitter system clock, the clock for the demultiplexer is derived from the received PAM signal itself.
A circuit called the clock recovery circuit is typical of those used to generate the demultiplexer clock pulses.
35. A TDM link has a fixed channel bandwidth of 100 kHz. ‘N’ signals are to be time division multiplexed, the signals have bandwidths of 10 kHz, 20 kHz, 30 kHz …….. N × 10 kHz. Assuming that signals are sampled at the Nyquist rate, the value of N is _____
4
3
2
1
Answer.1. 4
Explanation
Given channel bandwidth = 100 kHz
fs = 2 fm
fs = 2 × 10 + 2 × 20 + …. 2 × N × 10 —(1)
Channel bandwidth = fs/2
fs = 200 —(2)
from (1) and (2)
200 = 2 × 10 + 2 × 20 + …..2 × N × 10.
Sum of all natural number = N(N + 1)/2
10 = N(N + 1)/2
N = 4
36. _______ are used to reduce or stop synchronization problems while receiving?
Clock recovery circuits
Demodulators
Synchronizer
Bandpass filter
Answer.1. Clock recovery circuits
Explanation
The clock or symbol timing recovery is usually a closed-loop synchronizer, which attempts to lock a local clock signal onto the received data stream by the use of comparative measurements on the local and received signals.
Most communication systems transmit a sequence of 1s and 0s in an alternating pattern to enable the receiver to maintain bit synchronization.
A PLL operating at bit timing is used to maintain timing. Once the PLL is synchronized onto the received 101010 … pattern, it will remain synchronized onto any other patterns except for long sequences of all 0s or all 1s.
Clock recovery circuits are used to remedy the synchronization problem encountered in demultiplexing. The clock pulse is derived from the transmitted signal so that synchronization errors are reduced.
37. Which are non-orthogonal multiplexing?
TDM
FDM
TDM & FDM
Radar
Answer.1. TDM
Explanation
Non-orthogonal frequency-division multiplexing (N-OFDM) is a method of encoding digital data on multiple carrier frequencies with non-orthogonal intervals between frequency of sub-carriers. N-OFDM signals can be used in communication and radar systems.
Orthogonal Frequency-Division Multiplexing (OFDM) is a modulation technique for data transmission which has been known since the 1960s.
OFDM is based on splitting the data stream to be transmitted onto several orthogonal subcarriers and thereby allowing an increased symbol period. Since low-rate modulation schemes are more robust to multipath, it is more effective to transmit many low-rate streams in parallel than one single high-rate stream.
38. Which of the following is not an advantage of time-division multiplexing?
Signal interference is less
More flexible
Full channel can be used for every signal
Fast data transfer
Answer.4. Fast data transfer
Explanation
The disadvantage of using TDMA technology is that the users have a predefined time slot. When moving from one cell site to other, if all the time slots in this cell are full the user might be disconnected. Another problem in TDMA is that it is subjected to multipath distortion.
Since the time available for transmission is shared by all the signals that are modulated, Time-division multiplexing is not fast when compared with other multiplexing techniques.
39. ______ is used on links that use fiber optic technology.
TDM
FDM
WDM
CDMA
Answer.3. WDM
Explanation
WDM is used on links that use fiber optic technology. This scheme is similar to FDMA. Each user is allocated a pair of wavelengths, one wavelength for transmitting and another for receiving. Further, different users have different pairs of wavelengths.
40. ________ can be achieved by sending a pilot tone before sending the message signals.
Carrier Synchronization
Symbol Synchronization
Both 1 and 2
None of the above
Answer.1. Carrier Synchronization
Explanation
Carrier synchronization can be achieved by sending a pilot tone before sending the message signals. Since the pilot tone has a strong spectral line at the carrier frequency, the receiver can easily lock on it and generate a local coherent carrier.
However, this requires extra transmission bandwidth. Carrier synchronization also can be achieved with a carrier recovery circuit, which extracts the phase and frequency information from the noisy received signal and use it to generate a clean sinusoidal reference signal.
