Unit 3: Data Link Layer Flashcards
(26 cards)
What is the primary function of the data link layer?
The data link layer ensures reliable transmission of data frames between two nodes connected by a physical layer. It performs framing, error detection, flow control, and medium access control.
Why is framing necessary in data communication?
Framing divides the continuous stream of bits into manageable data units (frames) so that the receiver can identify frame boundaries and process data correctly.
What are the major design issues of the data link layer?
- Framing
- Error control
- Flow control
- Addressing
- Medium access control
What is the difference between error detection and error correction?
Error detection identifies the presence of errors in the transmitted data, while error correction identifies and fixes the errors without retransmission.
Why is error detection important in networking?
It ensures data integrity by identifying corrupted data during transmission, allowing for retransmission or correction.
What are common error detection techniques?
- Parity bits
- Checksum
- Cyclic Redundancy Check (CRC)
Why is CRC preferred over parity and checksum?
CRC detects more types of errors with higher accuracy and is computationally efficient for large data blocks.
What is a data frame?
A data frame is a structured packet of data that includes headers and trailers along with the actual payload to enable proper transmission and reception at the data link layer.
What are elementary data link protocols?
- Unrestricted simplex
- Stop-and-wait
- Sliding window protocols
What is the stop-and-wait protocol?
In stop-and-wait, the sender transmits a frame and waits for an acknowledgment before sending the next one. It is simple but inefficient for long delays.
What is the sliding window protocol?
Sliding window protocols allow the sender to send multiple frames before needing an acknowledgment, improving efficiency.
What is the difference between go-back-N and selective repeat protocols?
- Go-back-N: Sender resends all frames from the last unacknowledged one on error.
- Selective repeat: Only the specific erroneous or lost frame is retransmitted.
Why is selective repeat more efficient than go-back-N?
Selective repeat minimizes unnecessary retransmissions by resending only erroneous frames rather than all subsequent ones.
What is flow control in the data link layer?
Flow control prevents the sender from overwhelming the receiver by regulating data transmission rate.
What is HDLC (High-Level Data Link Control)?
HDLC is a bit-oriented, full-duplex data link layer protocol that uses a frame structure for reliable communication. It supports both point-to-point and multipoint links.
What are the different types of HDLC frames?
- Information (I) frames: carry user data
- Supervisory (S) frames: control flow and error
- Unnumbered (U) frames: carry control information
What is the purpose of frame check sequence (FCS) in HDLC?
FCS is a CRC-based field in the trailer that enables error detection in frames.
What is the channel allocation problem?
It refers to deciding how multiple users share a communication medium fairly and efficiently without conflicts.
What are multiple access protocols?
These protocols coordinate how devices share the same medium in a multi-access environment. Examples include ALOHA, CSMA, and token-based protocols.
What is ALOHA protocol?
ALOHA is a simple random-access protocol where stations transmit whenever they have data. Collisions are handled by retransmitting after random delays.
What is the difference between pure ALOHA and slotted ALOHA?
- Pure ALOHA: No synchronization; high collision rate.
- Slotted ALOHA: Time is divided into slots; transmissions only begin at slot boundaries, reducing collisions.
What is CSMA (Carrier Sense Multiple Access)?
In CSMA, a station listens to the channel before transmitting. If the channel is busy, it waits to avoid collision.
What is the difference between CSMA/CD and CSMA/CA?
- CSMA/CD (Collision Detection): Used in wired networks like Ethernet; detects collisions and retransmits.
- CSMA/CA (Collision Avoidance): Used in wireless networks like Wi-Fi; avoids collisions via signaling before transmission.
What is a token-passing protocol?
A token circulates in the network, and only the device holding the token can transmit. It prevents collisions and ensures fairness.
