What is flow control? Explain Stop and Wait ARQ with suitable example. How is it different from G Back N ARQ?

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Flow control is a data link layer technique that stops a fast sender from overwhelming a slow receiver. The sender may only send as much data as the receiver can accept, and waits for acknowledgements (ACKs) before sending more. ARQ (Automatic Repeat reQuest) adds error control: frames that are lost or damaged are sent again automatically. Stop and Wait ARQ 1. The sender sends one frame and keeps a copy of it. It starts a timer. 2. It waits for an ACK before sending the next frame. 3. The receiver sends an ACK when the frame arrives correctly. A damaged frame is discarded without an ACK. 4. If the timer expires before the ACK arrives, the sender retransmits the frame. 5. Frames and ACKs are numbered 0 and 1 (a 1 bit sequence number) so the receiver can spot a duplicate frame when an ACK was lost. Example: the sender sends Frame 0 and receives ACK 1, then sends Frame 1. Frame 1 is lost, so the timer expires and Frame 1 is sent again. ACK 0 arrives, and the sender sends the next Frame 0. It is simple, but the link is idle while the sender waits, so efficiency is poor on long or fast links. Stop and Wait vs Go Back N ARQ Stop and Wait ARQ Go Back N ARQ Sends one frame and waits for its ACK. Sends up to N frames (a window) before waiting. Sender window size = 1. Sender window size up to 2ᵐ − 1 (m = sequence bits). Sequence numbers 0 and 1. Sequence numbers 0 to 2ᵐ − 1. On error, only the one frame is resent. On error, the lost frame and all frames after it are resent. Low link utilisation. Much better utilisation (pipelining). Very simple; no buffering. Needs a sender buffer; the receiver accepts frames only in order.

What is flow control? Explain Stop and Wait ARQ with suitable example. How is it different from G Back N ARQ?

Stop-and-Wait ARQ

Stop-and-Wait vs Go-Back-N ARQ

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Stop-and-Wait ARQ	Go-Back-N ARQ
Sends one frame and waits for its ACK.	Sends up to N frames (a window) before waiting.
Sender window size = 1.	Sender window size up to 2ᵐ − 1 (m = sequence bits).
Sequence numbers 0 and 1.	Sequence numbers 0 to 2ᵐ − 1.
On error, only the one frame is resent.	On error, the lost frame and all frames after it are resent.
Low link utilisation.	Much better utilisation (pipelining).
Very simple; no buffering.	Needs a sender buffer; the receiver accepts frames only in order.