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:
- Send & Wait: The sender transmits a data frame and enters a "wait for ACK" state.
- 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.
- Retransmission: Upon receiving a NAK or timeout, the sender retransmits the same frame and restarts the "wait for ACK" state.
- 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.
