Stop-and-Wait Protocol: Simple Data Transmission with Acknowledgements

Understand the fundamentals of reliable data transmission with the Stop-and-Wait protocol. This guide explains its simple yet limited approach, outlining its operation, advantages (simplicity), and disadvantages (inefficiency), providing a foundational understanding of basic flow control mechanisms.

Stop-and-Wait Protocol: A Simple but Limited Approach to Reliable Data Transmission

What is the Stop-and-Wait Protocol?

The Stop-and-Wait protocol is a basic method for ensuring reliable data transmission between two devices. It's a simple, but inefficient, flow control mechanism that works by sending one data packet (or frame) at a time and waiting for an acknowledgment (ACK) from the receiver before transmitting the next packet. It's designed for use in relatively simple and noiseless environments and it does not include error detection or correction mechanisms.

How Stop-and-Wait Works

The process is straightforward:

  1. The sender transmits a data frame.
  2. The sender waits for an acknowledgment (ACK) from the receiver.
  3. Upon receiving the ACK, the sender transmits the next frame.
  4. This continues until all frames have been sent.

If the sender doesn't receive an ACK within a set time (a timeout), it retransmits the frame. The receiver sends an ACK only when it receives a complete and error-free frame.

Stop-and-Wait Protocol Primitives

The protocol operates with these rules:

Sender Side:

  • Transmits only one frame at a time.
  • Waits for an ACK before sending the next frame.

Receiver Side:

  • Receives and processes the frame.
  • Sends an ACK upon successful reception.

Limitations of Stop-and-Wait

The Stop-and-Wait protocol has several significant limitations, making it unsuitable for most real-world applications:

1. Lost Data or ACKs:

If a data packet or an ACK is lost, the sender will wait indefinitely for the ACK, and the receiver will wait indefinitely for the next packet, resulting in a standstill.

2. Delayed ACKs:

If an ACK is delayed, it might arrive after the sender’s timeout has expired, leading to unnecessary retransmissions.

3. Delayed Data Packets:

Similarly, if a data packet is delayed and arrives after the receiver's expected time, it may be rejected.

Conclusion

The Stop-and-Wait protocol is simple but highly inefficient for most networking scenarios due to its low throughput and high sensitivity to packet loss. More advanced protocols like Go-Back-N ARQ and Selective Repeat ARQ offer better performance and handle lost or corrupted packets more efficiently. Stop-and-Wait is primarily useful for illustrating fundamental concepts in data transmission but is not suitable for production environments.