Go-Back-N


  Go-Back-N.ppt (Size: 85 KB / Downloads: 0)

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

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

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