Difference Between Go-Back-N and Selective Repeat Protocol

Go-Back-N is a data link layer protocol that uses a sliding window method for reliable and sequential delivery of data frames. It has a sender window size of N and receiver window size of 1, meaning it can send N frames before requiring acknowledgment but processes frames sequentially at the receiver.

Selective Repeat Protocol is also a data link layer protocol that uses sliding window method for reliable delivery of data frames. Here, only the erroneous or lost frames are retransmitted, while correctly received frames are buffered and processed out-of-order.

Both protocols belong to the family of Automatic Repeat Request (ARQ) protocols and use sliding window mechanisms, but they differ significantly in their approaches to error recovery and frame management.

What is Go-Back-N Protocol?

The Go-Back-N ARQ protocol is a variant of the Automatic Repeat Request (ARQ) protocol that uses a simple retransmission strategy.

• Window-based transmission − The sender can transmit up to N frames without waiting for acknowledgments, determined by the sender window size.

• Sequential processing − The receiver has a window size of 1, meaning it accepts frames only in sequential order and discards out-of-order frames.

• Cumulative acknowledgments − The receiver sends cumulative ACKs, acknowledging all frames received correctly up to a specific sequence number.

• Complete retransmission − If a frame is lost or corrupted, all frames from that point onward (within the current window) are retransmitted, regardless of whether they were received correctly.

What is Selective Repeat Protocol?

Selective Repeat is a more efficient variant of ARQ that selectively retransmits only the frames that are lost or corrupted.

• Equal window sizes − Both sender and receiver maintain windows of equal size N, allowing more flexible frame management.

• Individual acknowledgments − Each frame is acknowledged individually, providing precise feedback about frame reception status.

• Out-of-order acceptance − The receiver can accept and buffer frames that arrive out of order, improving efficiency.

• Selective retransmission − Only the specific frames that are lost or corrupted are retransmitted, reducing unnecessary network traffic.

Comparison Between Go-Back-N and Selective Repeat Protocol

Key Advantages and Disadvantages

Go-Back-N Advantages

• Simple implementation − Requires minimal buffering at receiver and straightforward logic.

• Lower memory requirements − Receiver needs to store only one frame at a time.

Selective Repeat Advantages

• Better bandwidth utilization − Only retransmits frames that are actually lost or corrupted.

• Improved performance − Particularly effective in environments with high error rates or long propagation delays.

Conclusion

Go-Back-N is simpler to implement but less efficient due to unnecessary retransmissions when errors occur. Selective Repeat offers better bandwidth utilization by retransmitting only lost frames, making it more suitable for networks with higher error rates or bandwidth constraints, though it requires more complex implementation and memory management.