Computer Network | Sliding Window protocols Summary With Questions



Prerequisites – Stop & Wait, Go Back N, Selective Repeat

Summary of all the protocols –

Before starting with the questions a quick recap for all the protocols.

Stop and wait –

  1. Sender window size (Ws) = 1
  2. Receiver window size (Wr) = 1
  3. Sequence Number >= 1 + 1
  4. Uses independent acknowledgement
  5. Discards out of order packets
  6. Packet Loss → Retransmit packet after time out
  7. Acknowledgement loss → Resends packet after time out
  8. Efficiency = 1/(1+2a) where a = Tp/Tt

Go Back N –

  1. Sender window size Ws = N
  2. Receiver window size Wr = 1
  3. Sequence number >= N + 1
  4. Can use both cumulative or independent acknowledgement depends on acknowledge timer
  5. Discards out of order packets
  6. Packet Loss → Track back N size from the last packet within the window limit to the lost packet and retransmit them
  7. Acknowledgement loss → If not received before timeout the entire window N size is resend
  8. Efficiency = N/(1+2a) where a = Tp/Tt

Selective Repeat –

  1. Sender window size Ws = N
  2. Receiver window size Wr = N
  3. Sequence Number >= N + N
  4. Uses only independent acknowledgement
  5. Can Accept out of order packets
  6. Packet Loss → Resend only the lost packet after timeout
  7. Acknowledgement loss → Resend if not receive before timeout
  8. Efficiency = N/(1+2a) where a = Tp/Tt

Practice Questions –