Time Division Multiplexing (TDM) MCQ || TDM Questions and Answers

Answer.1. Commuter

Explanation

Multiplexers in early TDM/PAM telemetry systems used a form of rotary switch known as a commutator. A rotating switch called a commutator connects the output of each channel modulator to the input of the communication channel in turn.

The commutator is realized with electronic switches since it has to rotate at high speeds. The commutator remains at each contact for a fixed interval of time, which is the time slot allotted for each channel.

Answer.3. 1280 kbps

Explanation

Given sampling rate of channel each = 8000 Hz = fch

Since 24 such signals are Multiplexed, we get a total pulse per second (frequency) of the multiplied signal as:

fs = nfch

Putting on the respective values:

fs = 20 × 8000

fs = 160,000 = 160 KHz

Now each sample is represented by 7 bits and contains an additional bit for synchronization.

The total number of bits per sample will be:

n = 7 + 1 = 8 bits

∴ The total bit rate of TDM link will be:

Rb = nfs

Rb = 8 × 160 Kbps

Rb = 1280 Kilo-bits/sec

Answer.2. Delay is large

Explanation

Reservation systems are useful when Delay is large.

In the reservation scheme, a node is required to make a reservation prior to transmitting data. Time is split into intervals. In each interval, a reservation frame is initially sent.

Assume that there is n number of nodes. In this case, the reservation frame has precisely n number of mini time slots. Each mini time slot corresponds to a node.

If a node has sufficient data to send, it indicates its intention in its corresponding mini time slot. The nodes that made reservations, then transmit their data frames subsequent to the transmission of the reservation frame.

Answer.3. 2.5ms

Explanation

Time period for one frame = 1/100 = 0.01s = 10ms.

During that 10-ms frame period, each of the four channels is sampled once.

Each channel is thus allotted 10/4 = 2.5 ms.

Answer.3. Time-division multiplexing 

Explanation

In the time-division multiplexing (TDM) scheme, time is divided into frames of fixed duration. Each frame duration is further divided into a fixed number of time slots. Then, each node is allocated a fixed time slot within each frame period.

Thus a node is able to use the complete bandwidth of the medium for the duration of the time slot. This method transmits two or more digital signals or analog signals over a common channel.

However, it is possible for a time slot to be idle. Thus, this scheme does not use the channel resources efficiently. Observe that the TDM scheme is digital. This type of TDM is called synchronous TDM.

Answer.2. Asynchronous

Explanation

• In Asynchronous TDM, the sampling rate is different for each of the signals and a common clock is not required.
• In a slotted system, access is asynchronous and requires addressing information inside.
• If the allotted device for a time slot transmits nothing and sits idle, then that slot can be allotted to another device, unlike synchronous
• This type of TDM is used in Asynchronous transfer mode networks.

Answer.1. 24 kHz and 48 kbps

Explanation

Given:

f_m = 4 kHz

n = 6

Minimum transmission Bandwidth (B.W.) is given by equation (1)

B.W. = 6 × 4 = 24 kHz

f_s = 2 × 4 = 8 kHz

The bit rate for a PAM/TDM system is given by

Rb = nfs

R_b = 6 × 8 = 48 kHz

Answer.2. Greater

Explanation

CSMA stands for carrier sense multiple access, which means that every node on the network must monitor the bus for a period of no activity before trying to send a message on that bus (carrier sense).

The collision window is twice the cable length. The maximum time that is required to detect a collision (the collision window, or “slot time) is approximately equal to twice the signal propagation time between the two most-distant hosts on the network.

The contention window size of a node is doubled every time the packet transmitted by the node experiences a collision and is reset to its minimum value after every successful transmission. On detecting a collision, the node must wait for a random period of time before re-attempting to transmit.

Answer.1. Trigger all AND gates at clock frequency

Explanation

Monostable Multivibrators or “One-Shot Multivibrators” as they are also called, are used to generate a single output pulse of a specified width, either “HIGH” or “LOW” when a suitable external trigger signal or pulse T is applied.

The one-shot multivibrator is used to trigger all the decoder AND gates at the clock frequency. It produces an output pulse whose duration has been set to the desired sampling interval.

Answer.3. 0.33 ms

Explanation

In Synchronous TDM, frame duration is equal to bit duration

Frame duration = 1/Data Rate

Given

Data rate = 3 kbps.

Frame duration = 1/3 kbps

Frame duration = 0.33 msec.