Error/Flow Control Modeling (ARQ Modeling). Modeling of Go Back N.

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Presentation transcript:

Error/Flow Control Modeling (ARQ Modeling)

Modeling of Go Back N

© Tallal Elshabrawy 3 Limitation of Stop & Wait Protocol Inefficiency of Stop-and-Wait because the channel is left idle without use until an acknowledgement is received Potential Solution: Allowing the transmitter to continue sending enough frames so that the channel is kept busy while the transmitter is waiting for an acknowledgement Machine A Machine B Physical Channel First Frame-Bit enters Channel Last Frame-Bit enters Channel First Frame-Bit arrives at B Last Frame-Bit arrives at B Last ACK-Bit Arrives at A Processing Time Channel is Idle

© Tallal Elshabrawy 4 Go-Back-N ARQ Protocol Sender Receiver An outstanding frame: It is a frame that has been transmitted and is yet to be acknowledged Fr_0 Fr_1 Fr_2 Fr_3 Fr_4 Fr_5 Fr_6 ACK_1 ACK_2 ACK_3 Fr_3 Fr_4 Fr_5 Fr_6 Fr_7 Fr_8 ACK_4 ACK_5 ACK_6 ACK_7 ACK_8 Example Go Back 4 At this Point there are W S =4 Outstanding Frames. So, GO-BACK-4 Out of Sequence Frames. So, do not accept them

© Tallal Elshabrawy 5 Go-Back-N Basics Transmit without waiting for ACK Each frame received correctly is acknowledged with a sequence number corresponding to the NEXT frame expected The receiver discards all out of sequence packets If number of outstanding frames is W S : Go-Back-N

© Tallal Elshabrawy 6 What does W S Represent? W S is called the sending window size Each frame must be buffered (stored) until a valid ACK arrives (in case retransmission is needed) W S represents the maximum number of frames that may be outstanding (i.e., stored) simultaneously

© Tallal Elshabrawy 7 Sliding Window Concept Sender Receiver Fr_0 Fr_1 Fr_2 Fr_3 Fr_4 Fr_5 Fr_6 ACK_1 ACK_2 ACK_3 Example Go Back 4 Sending Window Frame Sequences that are allowed to be sent Outstanding Frame Sequences Fr_0 Fr_1 Fr_2 Fr_3 Go Back N is an example of what is called a sliding window protocol An ACK received means that all previous frames have been received correctly (previous ACKs were lost or receiver chose not to send them)

© Tallal Elshabrawy 8 Sliding Window Concept Sender Receiver Fr_0 Fr_1 Fr_2 Fr_3 Fr_4 Fr_5 Fr_6 ACK_1 ACK_2 ACK_3 Example Go Back 4 Sending Window Frame Sequences that are allowed to be sent Outstanding Frame Sequences Fr_0 Fr_1 Fr_2 Fr_3 Go Back N is an example of what is called a sliding window protocol An ACK received means that all previous frames have been received correctly (previous ACKs were lost or receiver chose not to send them)

© Tallal Elshabrawy 9 Sliding Window Concept Sender Receiver Fr_0 Fr_1 Fr_2 Fr_3 Fr_4 Fr_5 Fr_6 ACK_1 ACK_2 ACK_3 Example Go Back 4 Sending Window Frame Sequences that are allowed to be sent Outstanding Frame Sequences Fr_0 Fr_1 Fr_2 Fr_3 Go Back N is an example of what is called a sliding window protocol An ACK received means that all previous frames have been received correctly (previous ACKs were lost or receiver chose not to send them)

© Tallal Elshabrawy 10 Sliding Window Concept Sender Receiver Fr_0 Fr_1 Fr_2 Fr_3 Fr_4 Fr_5 Fr_6 ACK_1 ACK_2 ACK_3 Example Go Back 4 Sending Window Frame Sequences that are allowed to be sent Outstanding Frame Sequences Fr_0 Fr_1 Fr_2 Fr_3 Go Back N is an example of what is called a sliding window protocol An ACK received means that all previous frames have been received correctly (previous ACKs were lost or receiver chose not to send them)

© Tallal Elshabrawy 11 Sliding Window Concept Sender Receiver Fr_0 Fr_1 Fr_2 Fr_3 Fr_4 Fr_5 Fr_6 ACK_1 ACK_2 ACK_3 Example Go Back 4 Sending Window Frame Sequences that are allowed to be sent Outstanding Frame Sequences Fr_1 Fr_2 Fr_3 Fr_4 Go Back N is an example of what is called a sliding window protocol An ACK received means that all previous frames have been received correctly (previous ACKs were lost or receiver chose not to send them)

© Tallal Elshabrawy 12 Sliding Window Concept Sender Receiver Fr_0 Fr_1 Fr_2 Fr_3 Fr_4 Fr_5 Fr_6 ACK_1 ACK_2 ACK_3 Example Go Back 4 Sending Window Frame Sequences that are allowed to be sent Outstanding Frame Sequences Fr_2 Fr_3 Fr_4 Fr_5 Go Back N is an example of what is called a sliding window protocol An ACK received means that all previous frames have been received correctly (previous ACKs were lost or receiver chose not to send them)

© Tallal Elshabrawy 13 Sliding Window Concept Sender Receiver Fr_0 Fr_1 Fr_2 Fr_3 Fr_4 Fr_5 Fr_6 ACK_1 ACK_2 ACK_3 Example Go Back 4 Sending Window Frame Sequences that are allowed to be sent Outstanding Frame Sequences Fr_3 Fr_4 Fr_5 Fr_6 Go Back N is an example of what is called a sliding window protocol An ACK received means that all previous frames have been received correctly (previous ACKs were lost or receiver chose not to send them)

© Tallal Elshabrawy 14 Sliding Window Concept Sender Receiver Fr_0 Fr_1 Fr_2 Fr_3 Fr_4 Fr_5 Fr_6 ACK_1 ACK_2 ACK_3 Example Go Back 4 Sending Window Frame Sequences that are allowed to be sent Outstanding Frame Sequences Fr_4 Fr_5 Fr_6 Fr_7 ACK_4 Transmitter has nothing to send Go Back N is an example of what is called a sliding window protocol An ACK received means that all previous frames have been received correctly (previous ACKs were lost or receiver chose not to send them)

© Tallal Elshabrawy Go-Back-N ARQ Modeling 15 Machine A Machine B Physical Channel

© Tallal Elshabrawy Go-Back-N ARQ Markov Model 16

© Tallal Elshabrawy Go-Back-N ARQ Markov Model 17

© Tallal Elshabrawy Go-Back-N ARQ Throughput 18

© Tallal Elshabrawy S/W and GBN Comparison 19