Q.1 What is the main purpose of the Medium Access Control (MAC) sublayer in networking?
To route packets between networks
To control how devices access the shared communication medium
To manage IP addresses
To provide encryption for data
Explanation - The MAC sublayer is responsible for determining how multiple devices share the same physical medium, avoiding collisions and ensuring orderly communication.
Correct answer is: To control how devices access the shared communication medium
Q.2 Which MAC protocol uses a 'listen before talk' mechanism to avoid collisions?
ALOHA
CSMA
Token Ring
TDMA
Explanation - Carrier Sense Multiple Access (CSMA) requires a device to check if the channel is idle before transmitting to reduce collisions.
Correct answer is: CSMA
Q.3 In a CSMA/CD network, what happens when a collision is detected?
The device waits for a token
The device immediately retries without delay
The device stops transmission and retries after a random backoff period
The device ignores the collision
Explanation - CSMA/CD (Collision Detection) detects collisions, stops the current transmission, and waits for a random backoff before retransmitting to reduce repeated collisions.
Correct answer is: The device stops transmission and retries after a random backoff period
Q.4 Which LAN technology uses a token-passing mechanism for access control?
Ethernet
Wi-Fi
Token Ring
FDDI
Explanation - Token Ring networks pass a special data frame called a token around the network. Only the device holding the token can transmit, preventing collisions.
Correct answer is: Token Ring
Q.5 Which of the following is a disadvantage of pure ALOHA protocol?
Requires central control
High collision probability and low efficiency
Uses token for transmission
Needs synchronization between devices
Explanation - Pure ALOHA allows devices to transmit anytime, resulting in a high chance of collisions, leading to low channel utilization (around 18%).
Correct answer is: High collision probability and low efficiency
Q.6 What is the maximum efficiency of slotted ALOHA?
18%
36%
50%
25%
Explanation - Slotted ALOHA divides time into slots and allows transmission only at the start of each slot, doubling the efficiency of pure ALOHA to 36%.
Correct answer is: 36%
Q.7 Which IEEE standard defines Ethernet technology?
IEEE 802.3
IEEE 802.5
IEEE 802.11
IEEE 802.15
Explanation - IEEE 802.3 standard defines the specifications for Ethernet LANs, including cabling, signaling, and MAC protocols.
Correct answer is: IEEE 802.3
Q.8 In Ethernet, what is the typical size of a MAC address?
32 bits
48 bits
64 bits
128 bits
Explanation - Ethernet MAC addresses are 48 bits long, usually represented as 12 hexadecimal digits.
Correct answer is: 48 bits
Q.9 Which type of Ethernet allows multiple devices to transmit simultaneously without collisions?
Half-duplex Ethernet
Full-duplex Ethernet
Token Ring Ethernet
CSMA/CD Ethernet
Explanation - Full-duplex Ethernet allows simultaneous transmission and reception between devices over dedicated links, eliminating collisions.
Correct answer is: Full-duplex Ethernet
Q.10 Which LAN topology is inherently collision-free when using a token-passing protocol?
Bus
Ring
Star
Mesh
Explanation - In a ring topology using token-passing, only the device with the token can transmit, ensuring no collisions occur.
Correct answer is: Ring
Q.11 What is the main function of the MAC sublayer in CSMA/CD Ethernet?
Assign IP addresses to devices
Detect collisions and control access to the medium
Encrypt data for secure transmission
Convert analog signals to digital
Explanation - The MAC sublayer implements CSMA/CD rules to regulate access and detect collisions in Ethernet networks.
Correct answer is: Detect collisions and control access to the medium
Q.12 Which access method divides time into fixed slots for transmission?
TDMA
FDMA
CSMA/CD
ALOHA
Explanation - Time Division Multiple Access (TDMA) divides the medium into time slots, each allocated to a device to avoid collisions.
Correct answer is: TDMA
Q.13 Which of the following is a characteristic of FDDI networks?
Uses Ethernet frame format
Uses token-passing over a fiber optic ring
Primarily wireless
Based on CSMA/CD
Explanation - FDDI (Fiber Distributed Data Interface) is a high-speed LAN technology using a dual-ring fiber optic topology and token-passing for access control.
Correct answer is: Uses token-passing over a fiber optic ring
Q.14 Which of these improves Ethernet efficiency by avoiding collisions?
Using half-duplex mode
Using full-duplex mode
Reducing frame size to 64 bytes
Increasing the number of nodes
Explanation - Full-duplex Ethernet allows simultaneous send and receive operations, eliminating collisions and increasing efficiency.
Correct answer is: Using full-duplex mode
Q.15 Which LAN technology primarily uses CSMA/CA for access control?
Ethernet
Wi-Fi (IEEE 802.11)
Token Ring
FDDI
Explanation - Wi-Fi uses CSMA/CA (Collision Avoidance) because detecting collisions in a wireless medium is difficult.
Correct answer is: Wi-Fi (IEEE 802.11)
Q.16 What is the purpose of a backoff algorithm in CSMA/CD?
To encrypt data
To determine a random waiting period after a collision
To assign MAC addresses
To split the network into segments
Explanation - The backoff algorithm reduces the chance of repeated collisions by making devices wait a random time before retrying transmission.
Correct answer is: To determine a random waiting period after a collision
Q.17 Which MAC protocol is simplest but least efficient?
CSMA/CD
ALOHA
Token Ring
TDMA
Explanation - ALOHA allows devices to transmit anytime without coordination, leading to high collision rates and low efficiency.
Correct answer is: ALOHA
Q.18 In Ethernet, what is the minimum frame size and why?
64 bytes to detect collisions properly
128 bytes to support large payloads
512 bytes to match token ring
32 bytes to reduce latency
Explanation - Ethernet uses a minimum frame size of 64 bytes to ensure that collisions are detected while the frame is still being transmitted.
Correct answer is: 64 bytes to detect collisions properly
Q.19 Which LAN technology typically provides the highest data rate?
Ethernet
Token Ring
FDDI
Wi-Fi
Explanation - FDDI networks, using fiber optics and dual rings, can provide data rates up to 100 Mbps, which was higher than early Ethernet and Token Ring networks.
Correct answer is: FDDI
Q.20 Which statement about CSMA/CA is correct?
It detects collisions like CSMA/CD
It avoids collisions by using acknowledgments and waiting periods
It is used in wired Ethernet
It uses a token-passing mechanism
Explanation - CSMA/CA (Collision Avoidance) reduces collisions in wireless networks by waiting for an idle channel and using acknowledgment frames.
Correct answer is: It avoids collisions by using acknowledgments and waiting periods
Q.21 Which of the following is true for a star LAN topology?
All devices share the same collision domain
A central hub or switch connects all devices
It always uses token-passing
It cannot support full-duplex communication
Explanation - In a star topology, all devices connect to a central hub or switch, simplifying management and isolating collision domains when using switches.
Correct answer is: A central hub or switch connects all devices
Q.22 What type of MAC protocol is used in FDDI networks?
CSMA/CD
ALOHA
Token-passing
CSMA/CA
Explanation - FDDI uses token-passing to control access to the network, ensuring orderly transmission and high reliability over fiber optic rings.
Correct answer is: Token-passing
Q.23 Which factor primarily affects collision probability in Ethernet networks?
Network cable length
Number of devices sharing the medium
Frame size only
IP addressing scheme
Explanation - The more devices share the same medium, the higher the chance of collisions, especially in half-duplex Ethernet.
Correct answer is: Number of devices sharing the medium
Q.24 Which MAC protocol is better suited for wireless LANs?
CSMA/CD
CSMA/CA
Token Ring
TDMA
Explanation - Wireless LANs use CSMA/CA because collisions are hard to detect, so collision avoidance with acknowledgments is preferred.
Correct answer is: CSMA/CA
Q.25 In CSMA/CD, what is the typical behavior when the medium is busy?
Transmit immediately
Wait until the medium becomes idle
Switch to another medium
Send a token
Explanation - CSMA/CD devices sense the medium and wait until it is idle before transmitting to minimize collisions.
Correct answer is: Wait until the medium becomes idle