Automatic Repeat Algorithm

Stop and wait (time-out) ARQ is not an efficient way to use network bandwidth

Time-out

Time

Frame

ACK

Frame

Time-out

Time-out

Frame

ACK

Time-out

Frame

ACK

Time-out

Frame

ACK

Time-out

Frame

Time-out

Frame

ACK

Sender

Receiver

Sender

Receiver

Sender

Receiver

Sender

Receiver

ACK received

before timer

expires

Original frame

is lost

The ACK

is lost

Time-out

occurs too

soon

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