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Simplest Stop-And-Wait Stop-and-wait ARQ Go-back-N ARQ Selective- Repeat ARQ

philip-mccarthy
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Simplest Stop-And-Wait Stop-and-wait ARQ Go-back-N ARQ Selective- Repeat ARQ

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  1. Assume that a file is transferred from a node A to a node B. The file has been fragmented in 5 frames. Frame 0 is corrupted, the ACK of frame 1 is corrupted, ACK of frame 4 arrived after the time of frame 4 expired. Show the flow of frames exchanged between the two nodes, and the status of the windows after the transmission/reception of each information/control frame, if the field of sequence number is three-bit-length, and the sender and receiver are using the maximum possible window size, for the following data link control techniques: • Simplest • Stop-And-Wait • Stop-and-wait ARQ • Go-back-N ARQ • Selective- Repeat ARQ

  2. Simplest (ideal channel, no error) A B f0 f1 f2 f3 f4

  3. Stop and Wait in ideal channel (no error) A B f0 ACK 1 f1 ACK 0 f1 ACK 0 f0 ACK 1

  4. Stop and Wait ARQ A B f0 Time out f0 accepted ACK 1 f1 accepted ACK 0 f1 discarded ACK 0 f0 accepted ACK 1 f1 f1 accepted Time out ACK 0 discarded

  5. Go-Back-N ARQ A B 0 1 2 3 4 5 6 7 0 f0 0 1 2 3 4 5 6 7 8 f1 Time out f2 discarded f0 f1 discarded Time out ACK 1 f2 0 1 2 3 4 5 6 7 8 0 1 2 3 4 5 6 7 0 ACK 2 f1 f2 discarded f3 discarded 0 1 2 3 4 5 6 7 8 ACK 4 … 0 1 2 3 4 5 6 7 0 f4 ACK 5 0 1 2 3 4 5 6 7 8 Time out f4 … 0 1 2 3 4 5 6 7 0 discarded ACK 5

  6. Duplex Communication with Stop-and-Wait ARQ Assume that computer A and computer B communicate with each other. Each has 3 frames to send to the other. The three data frames sent by A are denoted as A1, A2, A3 and the frames from B are B1, B2, B3. They use duplex Stop-and-Wait ARQ for the communication, i.e., each data frame has a sequence # field and an Ack # field. Suppose each data frame needs 1 ms to transmit and each ack-only frame needs no time to transmit. The time-out value is set to be 5ms. The round trip time is always 2 ms. Use “A1, (0,1)” denote a frame with data A1 and sequence 0, ack 1.

  7. Ideal channel without any error/lost or congestion A B B1 B2 B3 A1 A2 A3

  8. Algorithm 11.5Sender-site algorithm for Stop-and-Wait ARQ (continued)

  9. (continued) Algorithm 11.5Sender-site algorithm for Stop-and-Wait ARQ

  10. Algorithm 11.6Receiver-site algorithm for Stop-and-Wait ARQ Protocol Rn is the sequence number of the next packet expected

  11. Stop-and-Wait ARQ Example Assume that computer A sends 3 frames to computer B. The three data frames sent by A are denoted as A1, A2, A3. Suppose each data frame needs 1 ms to transmit and each ack frame needs no time to transmit. The time-out value is set to be 4ms. The round trip time is always 2 ms. Use “A1, 0” denote a frame with data A1 and sequence 0. Use “Ack 1” denote an ack frame with ack number 1.

  12. Case 1: Ideal channel without any error/lost or congestion A B A1 A2 A3

  13. Case 2: second frame from A to B is lost A B A1 A2 A3

  14. Case 3: second frame from A to B uses 3 ms A B A1 A2 A3

  15. Case 4: second ack frame from B to A uses 3ms A B A1 A2 A3

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