DC 3 Flashcards
What are the key differences between asynchronous and synchronous transmission?
Asynchronous: Uses start/stop bits; suitable for small data; 20% overhead.
Synchronous: Uses frames with preamble/postamble; efficient for large data; requires clock synchronization.
How is synchronization achieved in synchronous transmission?
Through methods like Manchester encoding or embedding timing in the data signal (e.g., carrier phase alignment).
What are the two main types of transmission errors?
Single-bit error: Isolated bit alteration (e.g., due to noise).
Burst error: A sequence of erroneous bits (e.g., due to impulse noise).
What is the purpose of a parity bit?
To detect errors by ensuring an even/odd number of 1s in transmitted data. Ineffective for burst errors.
What is the difference between point-to-point and multipoint topologies?
Point-to-Point: Direct connection between two devices.
Multipoint: Multiple devices share a single link (e.g., in LANs).
What are half-duplex and full-duplex modes?
Half-Duplex: Alternating two-way communication (e.g., walkie-talkies).
Full-Duplex: Simultaneous two-way communication (e.g., telephone calls).
What are Stop-and-Wait and Sliding Window flow control techniques?
Stop-and-Wait: Sends one frame and waits for acknowledgment (simple but inefficient).
Sliding Window: Allows multiple frames to be sent before acknowledgment (efficient for large data).
What are the types of ARQ techniques?
Stop-and-Wait ARQ: Sends one frame at a time, retransmits after timeout.
Go-Back-N ARQ: Retransmits the frame in error and all subsequent frames.
Selective Reject ARQ: Only retransmits the frame in error (more efficient but complex).
What are the three station types in HDLC?
Primary Station: Controls link operation.
Secondary Station: Operates under the primary.
Combined Station: Both command and response capabilities.
What are HDLC link configurations and transfer modes?
Configurations: Unbalanced (primary/secondary) and balanced (combined stations).
Modes:
NRM (Normal Response Mode): Secondary responds to primary commands.
ABM (Asynchronous Balanced Mode): Both stations can initiate transmission.
ARM (Asynchronous Response Mode): Secondary can transmit without permission.
What is bit stuffing in HDLC, and why is it used?
Bit stuffing inserts a 0 after five consecutive 1s in the data to prevent the flag sequence (01111110) from appearing within the frame, maintaining synchronization.
What are key network performance metrics?
Bandwidth: Max data transferable per unit time.
Latency: Time delay for data transfer.
Jitter: Variation in data packet delay.
Packet Loss: Percentage of lost data packets.
Throughput: Effective data transfer rate.
Error Rate: Number of transmission errors.
Why is sliding window more efficient than stop-and-wait?
Sliding window treats the link as a pipeline, allowing multiple frames in transit, while stop-and-wait only allows one frame at a time, leading to underutilization.
What is the difference between Go-Back-N and Selective Reject ARQ?
Go-Back-N: Retransmits the error frame and all subsequent frames.
Selective Reject: Retransmits only the error frame, requiring more complex logic.
What are the main objectives of data link control protocols?
Frame synchronization, flow control, error control, addressing, control/data differentiation, and link management.
