This set of Computer Networks Multiple Choice Questions & Answers (MCQs) focuses on “Data Link Layer”.
1. The data link layer takes the packets from _________ and encapsulates them into frames for transmission.
a) network layer
b) physical layer
c) transport layer
d) application layer
View Answer
Explanation: In computer networks, the data from application layer is sent to transport layer and is converted to segments. These segments are then transferred to the network layer and these are called packets. These packets are then sent to data link layer where they are encapsulated into frames. These frames are then transferred to physical layer where the frames are converted to bits. Error control and flow control data is inserted in the frames at the data link layer.
2. Which of the following tasks is not done by data link layer?
a) framing
b) error control
c) flow control
d) channel coding
View Answer
Explanation: Channel coding is the function of physical layer. Data link layer mainly deals with framing, error control and flow control. Data link layer is the layer where the packets are encapsulated into frames.
3. Which sublayer of the data link layer performs data link functions that depend upon the type of medium?
a) logical link control sublayer
b) media access control sublayer
c) network interface control sublayer
d) error control sublayer
View Answer
Explanation: Media access control (MAC) deals with transmission of data packets to and from the network-interface card, and also to and from another remotely shared channel. The MAC sublayer also prevents collision using protocols like CSMA/CD.
4. Header of a frame generally contains ______________
a) synchronization bytes
b) addresses
c) frame identifier
d) all of the mentioned
View Answer
Explanation: In a frame, the header is a part of the data that contains all the required information about the transmission of the file. It contains information like synchronization bytes, addresses, frame identifier etc. It also contains error control information for reducing the errors in the transmitted frames.
5. Automatic repeat request error management mechanism is provided by ________
a) logical link control sublayer
b) media access control sublayer
c) network interface control sublayer
d) application access control sublayer
View Answer
Explanation: The logical link control is a sublayer of data link layer whose main function is to manage traffic, flow and error control. The automatic repeat request error management mechanism is provided by the LLC when an error is found in the received frame at the receiver’s end to inform the sender to re-send the frame.
6. When 2 or more bits in a data unit has been changed during the transmission, the error is called ____________
a) random error
b) burst error
c) inverted error
d) double error
View Answer
Explanation: When a single bit error occurs in a data, it is called single bit error. When more than a single bit of data is corrupted or has error, it is called burst error. If a single bit error occurs, the bit can be simply repaired by inverting it, but in case of a burst error, the sender has to send the frame again.
7. CRC stands for __________
a) cyclic redundancy check
b) code repeat check
c) code redundancy check
d) cyclic repeat check
View Answer
Explanation: Cyclic redundancy check is a code that is added to a data which helps us to identify any error that occurred during the transmission of the data. CRC is only able to detect errors, not correct them. CRC is inserted in the frame trailer.
8. Which of the following is a data link protocol?
a) ethernet
b) point to point protocol
c) hdlc
d) all of the mentioned
View Answer
Explanation: There are many data link layer protocols. Some of them are SDLC (synchronous data link protocol), HDLC (High level data link control), SLIP (serial line interface protocol), PPP (Point to point protocol) etc. These protocols are used to provide the logical link control function of the Data Link Layer.
9. Which of the following is the multiple access protocol for channel access control?
a) CSMA/CD
b) CSMA/CA
c) Both CSMA/CD & CSMA/CA
d) HDLC
View Answer
Explanation: In CSMA/CD, it deals with detection of collision after collision has occurred, whereas CSMA/CA deals with preventing collision. CSMA/CD is abbreviation for Carrier Sensing Multiple Access/Collision detection. CSMA/CA is abbreviation for Carrier Sensing Multiple Access/Collision Avoidance. These protocols are used for efficient multiple channel access.
10. The technique of temporarily delaying outgoing acknowledgements so that they can be hooked onto the next outgoing data frame is called ____________
a) piggybacking
b) cyclic redundancy check
c) fletcher’s checksum
d) parity check
View Answer
Explanation: Piggybacking is a technique in which the acknowledgment is temporarily delayed so as to be hooked with the next outgoing data frame. It saves a lot of channel bandwidth as in non-piggybacking system, some bandwidth is reserved for acknowledgement.
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