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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,

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Presentation on theme: "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,"— Presentation transcript:

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 AB f0 f1 f2 f3 f4 Simplest (ideal channel, no error)

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

4 Stop and Wait ARQ AB f0 ACK 1 f1 ACK 0 f1 Time out f0 f1 ACK 1 f1 ACK 0 accepted discarded accepted discarded

5 Go-Back-N ARQ AB f0 f1 ACK 1 ACK 2 ACK 4 f1 Time out f4 f3 ACK 5 discarded f2 discarded f f1 f discarded f Time out … …

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 AB A1A2 B1 A3 B2B3

8 11.8 Algorithm 11.5 Sender-site algorithm for Stop-and-Wait ARQ (continued)

9 11.9 Algorithm 11.5 Sender-site algorithm for Stop-and-Wait ARQ (continued)

10 11.10 Algorithm 11.6 Receiver-site algorithm for Stop-and-Wait ARQ Protocol R n 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 AB A1A2A3

13 Case 2: second frame from A to B is lost AB A1A2A3

14 Case 3: second frame from A to B uses 3 ms AB A1A2A3

15 Case 4: second ack frame from B to A uses 3ms AB A1A2A3


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