Advantages and Disadvantages of STOP & WAIT ARQ for Network Communication

Stop-and-Wait (S&W) ARQ, also known as the alternating bit protocol, is a simple and reliable method for data transmission over unreliable channels. It ensures accurate and in-order delivery of data packets by implementing mechanisms for error detection, flow control, and retransmission.

Core principles of S&W ARQ:

• Sender-driven mechanism: The sender actively transmits data and manages the communication process.
• Single outstanding frame: The sender can only transmit and have one data frame (a packet) outstanding at a time.
• ACK/NAK signals: The receiver acknowledges successful reception with an ACK (Acknowledgement) signal or requests retransmission with a NAK (Negative Acknowledgement) signal.
• Timeout mechanism: If the sender doesn't receive an ACK/NAK within a specified timeout period, it assumes the previous frame is lost and retransmits it.

Operation of S&W ARQ:

1. Send & Wait: The sender transmits a data frame and enters a "wait for ACK" state.
2. ACK/NAK Reception:
   • ACK: The receiver successfully receives the frame and sends an ACK back to the sender.
   • NAK/Timeout: If the frame is corrupted or lost, the receiver sends a NAK or the sender's timer times out, triggering retransmission.
3. Retransmission: Upon receiving a NAK or timeout, the sender retransmits the same frame and restarts the "wait for ACK" state.
4. Flow control: The receiver can implicitly control the sender's transmission rate by delaying ACKs, allowing its buffer to manage incoming data.

Advantages of S&W ARQ:

• Simple and efficient: Easy to implement and understand, ideal for introductory learning.
• Reliable: Guarantees accurate and in-order delivery with error detection and retransmission.
• Low overhead: Requires minimal control information exchange compared to other protocols.

Disadvantages of S&W ARQ:

• Low channel utilization: Only one frame can be in transit at a time, leading to idle periods and reduced throughput.
• Increased latency: Additional waiting and retransmission cycles lengthen the overall transmission time.
• Unsuitable for high bandwidth networks: Inefficient for large data transfers due to limited channel utilization.

Applications of S&W ARQ:

• Used in low-bandwidth, reliable communication channels, like satellite links and data acquisition systems.
• Serves as a foundation for understanding more complex ARQ protocols like Go-Back-N and Selective Repeat.