Switching Networks And Data Link Layer Core Fundamentals Practice Tests

Question 1

A link has a total capacity of $C = 20$ Mbps. If $N$ users each require a dedicated circuit of $R = 4$ Mbps, calculate the maximum number of simultaneous sessions $N$ that can be supported. If a new request arrives when $N$ sessions are active, what is the probability of the request being accepted?

Accepted Answer

5 sessions; 0 probability

Answer

4 sessions; 0.2 probability

Answer

20 sessions; 1 probability

Answer

5 sessions; 0.2 probability

Question 2

In a circuit-switched network, a transmission path consists of 3 links, each with a propagation delay of $d_p = 10$ ms. If the setup phase takes $t_s = 50$ ms and the teardown phase takes $t_t = 20$ ms, calculate the total time $T$ required to transmit a file of size $L = 10^6$ bits over a link with bandwidth $B = 1$ Mbps.

Accepted Answer

1080 ms

Question 3

In a circuit-switched network, if the probability of any single link being busy is $p = 0.1$, the probability that a 3-link path is available is $(1-p)^3 = 0.729$.

Accepted Answer

True

Answer

False

Question 4

Consider a packet-switched network where packets of size $L = 1500$ bytes arrive at a switch with a service rate of $\mu = 10^6$ packets per second. If the arrival rate is $\lambda = 8 	imes 10^5$ packets per second, calculate the utilization $ho$ of the switch.

Accepted Answer

0.8

Answer

0.2

Answer

0.75

Answer

1.25

Question 5

A switch buffer has a capacity of $K = 10$ packets. If packets arrive at a rate $\lambda$ and are processed at rate $\mu$, and the current queue length is $Q = 9$, what is the probability of packet loss for the next arriving packet if the arrival process is deterministic?

Accepted Answer

0

Question 6

Which of the following scenarios favor the use of datagram packet switching over circuit switching? (Select all that apply)

Answer

Traffic is highly bursty with long idle periods

Answer

The network must remain operational despite individual node failures

Answer

Applications require minimal setup latency for short-lived messages

Answer

Applications require a strictly constant bit rate and zero jitter

Question 7

In a virtual circuit network, a switch receives a packet with VCI = 5 on Port 1. The forwarding table maps (Port 1, VCI 5) to (Port 3, VCI 12). If the packet header is modified to VCI 12, what is the primary purpose of this modification?

Accepted Answer

To identify the virtual circuit on the next hop

Answer

To increase the packet size

Answer

To calculate the checksum for error detection

Answer

To determine the final destination IP address

Question 8

A virtual circuit path is established across 4 switches. If the signaling message to set up the path takes $T_{setup} = 20$ ms per hop, calculate the total time to establish the circuit.

Accepted Answer

80 ms

Question 9

In virtual circuit switching, if a link failure occurs, the forwarding tables of all switches along the path must be updated to reflect the new route or the connection must be re-established.

Accepted Answer

True

Answer

False

Question 10

Compare the header overhead of a datagram packet vs. a virtual circuit packet. If a datagram header is $H_d = 20$ bytes and a VC header is $H_{vc} = 4$ bytes, and a file is split into $N = 1000$ packets, calculate the total header overhead saved by using VC switching.

Accepted Answer

16,000 bytes

Answer

4,000 bytes

Answer

20,000 bytes

Answer

24,000 bytes

Question 11

If a frame uses a byte-count method where the first byte represents the total number of bytes in the frame, and the header itself is included in the count, calculate the total frame size if the header value is $N = 128$.

Accepted Answer

128 bytes

Answer

127 bytes

Answer

129 bytes

Answer

256 bytes

Question 12

A data stream contains the sequence of bytes: [FLAG, DATA, ESC, FLAG]. Apply byte stuffing using the rule: replace FLAG with ESC FLAG and ESC with ESC ESC. Provide the resulting byte sequence.

Accepted Answer

ESC FLAG, DATA, ESC ESC, ESC FLAG

Question 13

In bit stuffing, a flag sequence is defined as $01111110$. If the raw data contains the sequence $011111110$, what is the transmitted sequence after bit stuffing to prevent false flag detection?

Accepted Answer

Option A

Answer

Option B

Answer

Option C

Answer

Option D

Question 14

If the byte-count field in a frame is corrupted during transmission, the receiver can maintain synchronization for subsequent frames by using the remaining bits to calculate the next frame's start.

Accepted Answer

False

Answer

True

Question 15

A Network Interface Card (NIC) processes a datagram of size $L$ bytes. If the overhead of the DLL framing is $H$ bytes, what is the total frame size $S$ in terms of $L$ and $H$?

Accepted Answer

$S = L + H$

Answer

$S = L - H$

Answer

$S = L 	imes H$

Answer

$S = \frac{L}{H}$

Question 16

Given a raw bit stream $11111111$, apply bit stuffing for the flag $01111110$. What is the resulting bit stream?

Accepted Answer

111110111

Question 17

Which of the following are primary reasons for implementing the Data Link Layer in hardware (NIC) rather than software?

Answer

High-speed processing requirements

Answer

Direct interaction with physical signaling media

Answer

Ease of updating protocol logic

Answer

Reduced power consumption in all scenarios

Question 18

If a system uses byte stuffing where FLAG = 0x7E and ESC = 0x7D, represent the stuffed version of the data byte 0x7D.

Accepted Answer

0x7D 0x7D

Question 19

Consider a transmission where the probability of a single bit error is $p = 10^{-5}$. If a frame consists of $n = 1000$ bits, what is the probability $P$ that the frame is received without any errors?

Accepted Answer

$P = (1 - 10^{-5})^{1000}$

Answer

$P = 1 - (10^{-5})^{1000}$

Answer

$P = 10^{-5} 	imes 1000$

Answer

$P = 1 - 10^{-5} 	imes 1000$

Question 20

In bit stuffing, the receiver must remove the stuffed bit only if it follows a sequence of five consecutive ones and is immediately followed by a zero.

Accepted Answer

True

Answer

False

Switching Networks And Data Link Layer Core Fundamentals Practice Tests

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Switching Networks and Data Link Layer Core Fundamentals

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