Flow control (stop-and-wait, sliding window) in Computer Networks - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Stop-and-Wait Flow Control

In a stop-and-wait flow control protocol, what happens immediately after the sender transmits a data frame?

A The sender sends multiple frames at once and waits for acknowledgments.

B The sender immediately sends the next frame without waiting.

C The sender waits for an acknowledgment before sending the next frame.

D The sender closes the connection after sending one frame.

💡 Hint

Think about how the sender ensures the receiver got the data before continuing.

In stop-and-wait, the sender sends one frame and waits for an acknowledgment before sending the next. This prevents overwhelming the receiver.

📋 Factual

intermediate

Sliding Window Protocol Window Size

What is the main advantage of using a sliding window protocol with a window size greater than one?

A It allows multiple frames to be sent before waiting for acknowledgments, increasing throughput.

B It reduces the number of frames sent to one per connection.

C It guarantees zero packet loss in the network.

D It requires the sender to wait for each acknowledgment before sending any frame.

💡 Hint

Consider how sending multiple frames without waiting affects data flow.

A sliding window with size greater than one lets the sender send several frames before needing acknowledgments, improving efficiency and throughput.

🔍 Analysis

advanced

Effect of Window Size on Network Utilization

Given a network with a high round-trip time (RTT), which sliding window size will maximize utilization without causing buffer overflow at the receiver?

A A window size larger than the receiver's buffer size.

B A window size equal to the bandwidth-delay product of the network.

C A window size of 1, to avoid any congestion.

D A window size of zero, to stop all transmissions.

💡 Hint

Think about how the bandwidth-delay product relates to data in transit.

The bandwidth-delay product represents the amount of data that can fill the network pipe. Setting the window size to this value maximizes utilization without overflow.

❓ Comparison

advanced

Comparing Stop-and-Wait and Sliding Window Protocols

Which statement correctly compares stop-and-wait and sliding window flow control protocols?

A Stop-and-wait sends one frame at a time and waits for acknowledgment; sliding window sends multiple frames before waiting.

B Stop-and-wait uses a window size greater than one; sliding window uses a window size of one.

C Both protocols send multiple frames without waiting for acknowledgments.

D Sliding window sends one frame at a time; stop-and-wait sends multiple frames before waiting.

💡 Hint

Focus on how many frames each protocol sends before waiting.

Stop-and-wait sends one frame and waits for acknowledgment before sending the next. Sliding window allows multiple frames to be sent before waiting.

❓ Reasoning

expert

Impact of Lost Acknowledgments in Sliding Window

In a sliding window protocol, if an acknowledgment for a frame is lost but the frame was received correctly, what is the most likely outcome?

A The sender will ignore the lost acknowledgment and continue sending new frames.

B The sender will stop sending any further frames permanently.

C The receiver will discard all future frames until the acknowledgment is received.

D The sender will retransmit the frame, causing a duplicate at the receiver.

💡 Hint

Consider how the sender detects lost acknowledgments and what it does next.

If an acknowledgment is lost, the sender assumes the frame was not received and retransmits it. The receiver may get a duplicate but can detect and discard it.