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Go-Back-N (GBN)

Go-Back-N (GBN). Yan Gao Feb. 17, 2006. Go-Back-N protocol. Concept Introduce a window of size n Can inject n packets into net before hearing an ACK Sliding window Label each packet with a sequence number A window is a collection of adjacent sequence numbers

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Go-Back-N (GBN)

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  1. Go-Back-N (GBN) Yan Gao Feb. 17, 2006

  2. Go-Back-N protocol • Concept • Introduce a window of size n • Can inject n packets into net before hearing an ACK • Sliding window • Label each packet with a sequence number • A window is a collection of adjacent sequence numbers • The size of the collection is the sender’s window size

  3. Example

  4. Example

  5. Example

  6. Receive Window Maintenance • Receiver keeps a similar window • Receiver has a finite buffer • Let window edge is first packet receiver wants to see • Right window edge is last packet it can hold • Packets < left edge or > right edge dropped • Other packets are queued, allowing for fixing up out-of-order packets

  7. Example

  8. Go-Back-N • Sender has to buffer all unacknowledged packets, because they may require retransmission. • Receiver may be able to accept out-of-order packets, but only up to its buffer limits. • The sender needs to set timers in order to know when to retransmit a packet that may have been lost

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